// SPDX-License-Identifier: GPL-2.0-only
/*
 * Copyright (C) 2011 Novell Inc.
 * Copyright (C) 2016 Red Hat, Inc.
 */

#include <linux/fs.h>
#include <linux/cred.h>
#include <linux/ctype.h>
#include <linux/hex.h>
#include <linux/namei.h>
#include <linux/xattr.h>
#include <linux/ratelimit.h>
#include <linux/mount.h>
#include <linux/exportfs.h>
#include "overlayfs.h"

struct ovl_lookup_data {
        struct super_block *sb;
        struct dentry *dentry;
        const struct ovl_layer *layer;
        struct qstr name;
        bool is_dir;
        bool opaque;
        bool xwhiteouts;
        bool stop;
        bool last;
        char *redirect;
        char *upperredirect;
        int metacopy;
        /* Referring to last redirect xattr */
        bool absolute_redirect;
};

static int ovl_check_redirect(const struct path *path, struct ovl_lookup_data *d,
                              size_t prelen, const char *post)
{
        int res;
        char *buf;
        struct ovl_fs *ofs = OVL_FS(d->sb);

        d->absolute_redirect = false;
        buf = ovl_get_redirect_xattr(ofs, path, prelen + strlen(post));
        if (IS_ERR_OR_NULL(buf))
                return PTR_ERR(buf);

        if (buf[0] == '/') {
                d->absolute_redirect = true;
                /*
                 * One of the ancestor path elements in an absolute path
                 * lookup in ovl_lookup_layer() could have been opaque and
                 * that will stop further lookup in lower layers (d->stop=true)
                 * But we have found an absolute redirect in descendant path
                 * element and that should force continue lookup in lower
                 * layers (reset d->stop).
                 */
                d->stop = false;
        } else {
                res = strlen(buf) + 1;
                memmove(buf + prelen, buf, res);
                memcpy(buf, d->name.name, prelen);
        }

        strcat(buf, post);
        kfree(d->redirect);
        d->redirect = buf;
        d->name.name = d->redirect;
        d->name.len = strlen(d->redirect);

        return 0;
}

static int ovl_acceptable(void *ctx, struct dentry *dentry)
{
        /*
         * A non-dir origin may be disconnected, which is fine, because
         * we only need it for its unique inode number.
         */
        if (!d_is_dir(dentry))
                return 1;

        /* Don't decode a deleted empty directory */
        if (d_unhashed(dentry))
                return 0;

        /* Check if directory belongs to the layer we are decoding from */
        return is_subdir(dentry, ((struct vfsmount *)ctx)->mnt_root);
}

/*
 * Check validity of an overlay file handle buffer.
 *
 * Return 0 for a valid file handle.
 * Return -ENODATA for "origin unknown".
 * Return <0 for an invalid file handle.
 */
int ovl_check_fb_len(struct ovl_fb *fb, int fb_len)
{
        if (fb_len < sizeof(struct ovl_fb) || fb_len < fb->len)
                return -EINVAL;

        if (fb->magic != OVL_FH_MAGIC)
                return -EINVAL;

        /* Treat larger version and unknown flags as "origin unknown" */
        if (fb->version > OVL_FH_VERSION || fb->flags & ~OVL_FH_FLAG_ALL)
                return -ENODATA;

        /* Treat endianness mismatch as "origin unknown" */
        if (!(fb->flags & OVL_FH_FLAG_ANY_ENDIAN) &&
            (fb->flags & OVL_FH_FLAG_BIG_ENDIAN) != OVL_FH_FLAG_CPU_ENDIAN)
                return -ENODATA;

        return 0;
}

static struct ovl_fh *ovl_get_fh(struct ovl_fs *ofs, struct dentry *upperdentry,
                                 enum ovl_xattr ox)
{
        int res, err;
        struct ovl_fh *fh = NULL;

        res = ovl_getxattr_upper(ofs, upperdentry, ox, NULL, 0);
        if (res < 0) {
                if (res == -ENODATA || res == -EOPNOTSUPP)
                        return NULL;
                goto fail;
        }
        /* Zero size value means "copied up but origin unknown" */
        if (res == 0)
                return NULL;

        fh = kzalloc(res + OVL_FH_WIRE_OFFSET, GFP_KERNEL);
        if (!fh)
                return ERR_PTR(-ENOMEM);

        res = ovl_getxattr_upper(ofs, upperdentry, ox, fh->buf, res);
        if (res < 0)
                goto fail;

        err = ovl_check_fb_len(&fh->fb, res);
        if (err < 0) {
                if (err == -ENODATA)
                        goto out;
                goto invalid;
        }

        return fh;

out:
        kfree(fh);
        return NULL;

fail:
        pr_warn_ratelimited("failed to get origin (%i)\n", res);
        goto out;
invalid:
        pr_warn_ratelimited("invalid origin (%*phN)\n", res, fh);
        goto out;
}

bool ovl_uuid_match(struct ovl_fs *ofs, const struct super_block *sb,
                    const uuid_t *uuid)
{
        /*
         * Make sure that the stored uuid matches the uuid of the lower
         * layer where file handle will be decoded.
         * In case of uuid=off option just make sure that stored uuid is null.
         */
        return ovl_origin_uuid(ofs) ? uuid_equal(uuid, &sb->s_uuid) :
                                      uuid_is_null(uuid);
}

struct dentry *ovl_decode_real_fh(struct ovl_fs *ofs, struct ovl_fh *fh,
                                  struct vfsmount *mnt, bool connected)
{
        struct dentry *real;
        int bytes;

        if (!capable(CAP_DAC_READ_SEARCH))
                return NULL;

        if (!ovl_uuid_match(ofs, mnt->mnt_sb, &fh->fb.uuid))
                return NULL;

        bytes = (fh->fb.len - offsetof(struct ovl_fb, fid));
        real = exportfs_decode_fh(mnt, (struct fid *)fh->fb.fid,
                                  bytes >> 2, (int)fh->fb.type,
                                  connected ? ovl_acceptable : NULL, mnt);
        if (IS_ERR(real)) {
                /*
                 * Treat stale file handle to lower file as "origin unknown".
                 * upper file handle could become stale when upper file is
                 * unlinked and this information is needed to handle stale
                 * index entries correctly.
                 */
                if (real == ERR_PTR(-ESTALE) &&
                    !(fh->fb.flags & OVL_FH_FLAG_PATH_UPPER))
                        real = NULL;
                return real;
        }

        if (ovl_dentry_weird(real)) {
                dput(real);
                return NULL;
        }

        return real;
}

static struct dentry *ovl_lookup_positive_unlocked(struct ovl_lookup_data *d,
                                                   const char *name,
                                                   struct dentry *base, int len,
                                                   bool drop_negative)
{
        struct dentry *ret = lookup_one_unlocked(mnt_idmap(d->layer->mnt),
                                                 &QSTR_LEN(name, len), base);

        if (!IS_ERR(ret) && d_flags_negative(smp_load_acquire(&ret->d_flags))) {
                if (drop_negative && ret->d_lockref.count == 1) {
                        spin_lock(&ret->d_lock);
                        /* Recheck condition under lock */
                        if (d_is_negative(ret) && ret->d_lockref.count == 1)
                                __d_drop(ret);
                        spin_unlock(&ret->d_lock);
                }
                dput(ret);
                ret = ERR_PTR(-ENOENT);
        }
        return ret;
}

static int ovl_lookup_single(struct dentry *base, struct ovl_lookup_data *d,
                             const char *name, unsigned int namelen,
                             size_t prelen, const char *post,
                             struct dentry **ret, bool drop_negative)
{
        struct ovl_fs *ofs = OVL_FS(d->sb);
        struct dentry *this = NULL;
        const char *warn;
        struct path path;
        int err;
        bool last_element = !post[0];
        bool is_upper = d->layer->idx == 0;
        char val;

        /*
         * We allow filesystems that are case-folding capable as long as the
         * layers are consistently enabled in the stack, enabled for every dir
         * or disabled in all dirs. If someone has modified case folding on a
         * directory on underlying layer, the warranty of the ovl stack is
         * voided.
         */
        if (ofs->casefold != ovl_dentry_casefolded(base)) {
                warn = "parent wrong casefold";
                err = -ESTALE;
                goto out_warn;
        }

        this = ovl_lookup_positive_unlocked(d, name, base, namelen, drop_negative);
        if (IS_ERR(this)) {
                err = PTR_ERR(this);
                this = NULL;
                if (err == -ENOENT || err == -ENAMETOOLONG)
                        goto out;
                goto out_err;
        }

        if (ofs->casefold != ovl_dentry_casefolded(this)) {
                warn = "child wrong casefold";
                err = -EREMOTE;
                goto out_warn;
        }

        if (ovl_dentry_weird(this)) {
                /* Don't support traversing automounts and other weirdness */
                warn = "unsupported object type";
                err = -EREMOTE;
                goto out_warn;
        }

        path.dentry = this;
        path.mnt = d->layer->mnt;
        if (ovl_path_is_whiteout(ofs, &path)) {
                d->stop = d->opaque = true;
                goto put_and_out;
        }
        /*
         * This dentry should be a regular file if previous layer lookup
         * found a metacopy dentry.
         */
        if (last_element && d->metacopy && !d_is_reg(this)) {
                d->stop = true;
                goto put_and_out;
        }

        if (!d_can_lookup(this)) {
                if (d->is_dir || !last_element) {
                        d->stop = true;
                        goto put_and_out;
                }
                err = ovl_check_metacopy_xattr(ofs, &path, NULL);
                if (err < 0)
                        goto out_err;

                d->metacopy = err;
                d->stop = !d->metacopy;
                if (!d->metacopy || d->last)
                        goto out;
        } else {
                if (ovl_lookup_trap_inode(d->sb, this)) {
                        /* Caught in a trap of overlapping layers */
                        warn = "overlapping layers";
                        err = -ELOOP;
                        goto out_warn;
                }

                if (last_element)
                        d->is_dir = true;
                if (d->last)
                        goto out;

                /* overlay.opaque=x means xwhiteouts directory */
                val = ovl_get_opaquedir_val(ofs, &path);
                if (last_element && !is_upper && val == 'x') {
                        d->xwhiteouts = true;
                        ovl_layer_set_xwhiteouts(ofs, d->layer);
                } else if (val == 'y') {
                        d->stop = true;
                        if (last_element)
                                d->opaque = true;
                        goto out;
                }
        }
        err = ovl_check_redirect(&path, d, prelen, post);
        if (err)
                goto out_err;
out:
        *ret = this;
        return 0;

put_and_out:
        dput(this);
        this = NULL;
        goto out;

out_warn:
        pr_warn_ratelimited("failed lookup in %s (%pd2, name='%.*s', err=%i): %s\n",
                            is_upper ? "upper" : "lower", base,
                            namelen, name, err, warn);
out_err:
        dput(this);
        return err;
}

static int ovl_lookup_layer(struct dentry *base, struct ovl_lookup_data *d,
                            struct dentry **ret, bool drop_negative)
{
        /* Counting down from the end, since the prefix can change */
        size_t rem = d->name.len - 1;
        struct dentry *dentry = NULL;
        int err;

        if (d->name.name[0] != '/')
                return ovl_lookup_single(base, d, d->name.name, d->name.len,
                                         0, "", ret, drop_negative);

        while (!IS_ERR_OR_NULL(base) && d_can_lookup(base)) {
                const char *s = d->name.name + d->name.len - rem;
                const char *next = strchrnul(s, '/');
                size_t thislen = next - s;
                bool end = !next[0];

                /* Verify we did not go off the rails */
                if (WARN_ON(s[-1] != '/'))
                        return -EIO;

                err = ovl_lookup_single(base, d, s, thislen,
                                        d->name.len - rem, next, &base,
                                        drop_negative);
                dput(dentry);
                if (err)
                        return err;
                dentry = base;
                if (end)
                        break;

                rem -= thislen + 1;

                if (WARN_ON(rem >= d->name.len))
                        return -EIO;
        }
        *ret = dentry;
        return 0;
}

static int ovl_lookup_data_layer(struct dentry *dentry, const char *redirect,
                                 const struct ovl_layer *layer,
                                 struct path *datapath)
{
        int err;

        err = vfs_path_lookup(layer->mnt->mnt_root, layer->mnt, redirect,
                        LOOKUP_BENEATH | LOOKUP_NO_SYMLINKS | LOOKUP_NO_XDEV,
                        datapath);
        pr_debug("lookup lowerdata (%pd2, redirect=\"%s\", layer=%d, err=%i)\n",
                 dentry, redirect, layer->idx, err);

        if (err)
                return err;

        err = -EREMOTE;
        if (ovl_dentry_weird(datapath->dentry))
                goto out_path_put;

        err = -ENOENT;
        /* Only regular file is acceptable as lower data */
        if (!d_is_reg(datapath->dentry))
                goto out_path_put;

        return 0;

out_path_put:
        path_put(datapath);

        return err;
}

/* Lookup in data-only layers by absolute redirect to layer root */
static int ovl_lookup_data_layers(struct dentry *dentry, const char *redirect,
                                  struct ovl_path *lowerdata)
{
        struct ovl_fs *ofs = OVL_FS(dentry->d_sb);
        const struct ovl_layer *layer;
        struct path datapath;
        int err = -ENOENT;
        int i;

        layer = &ofs->layers[ofs->numlayer - ofs->numdatalayer];
        for (i = 0; i < ofs->numdatalayer; i++, layer++) {
                err = ovl_lookup_data_layer(dentry, redirect, layer, &datapath);
                if (!err) {
                        mntput(datapath.mnt);
                        lowerdata->dentry = datapath.dentry;
                        lowerdata->layer = layer;
                        return 0;
                }
        }

        return err;
}

int ovl_check_origin_fh(struct ovl_fs *ofs, struct ovl_fh *fh, bool connected,
                        struct dentry *upperdentry, struct ovl_path **stackp)
{
        struct dentry *origin = NULL;
        int i;

        for (i = 1; i <= ovl_numlowerlayer(ofs); i++) {
                /*
                 * If lower fs uuid is not unique among lower fs we cannot match
                 * fh->uuid to layer.
                 */
                if (ofs->layers[i].fsid &&
                    ofs->layers[i].fs->bad_uuid)
                        continue;

                origin = ovl_decode_real_fh(ofs, fh, ofs->layers[i].mnt,
                                            connected);
                if (origin)
                        break;
        }

        if (!origin)
                return -ESTALE;
        else if (IS_ERR(origin))
                return PTR_ERR(origin);

        if (upperdentry && !ovl_upper_is_whiteout(ofs, upperdentry) &&
            inode_wrong_type(d_inode(upperdentry), d_inode(origin)->i_mode))
                goto invalid;

        if (!*stackp)
                *stackp = kmalloc_obj(struct ovl_path);
        if (!*stackp) {
                dput(origin);
                return -ENOMEM;
        }
        **stackp = (struct ovl_path){
                .dentry = origin,
                .layer = &ofs->layers[i]
        };

        return 0;

invalid:
        pr_warn_ratelimited("invalid origin (%pd2, ftype=%x, origin ftype=%x).\n",
                            upperdentry, d_inode(upperdentry)->i_mode & S_IFMT,
                            d_inode(origin)->i_mode & S_IFMT);
        dput(origin);
        return -ESTALE;
}

static int ovl_check_origin(struct ovl_fs *ofs, struct dentry *upperdentry,
                            struct ovl_path **stackp)
{
        struct ovl_fh *fh = ovl_get_fh(ofs, upperdentry, OVL_XATTR_ORIGIN);
        int err;

        if (IS_ERR_OR_NULL(fh))
                return PTR_ERR(fh);

        err = ovl_check_origin_fh(ofs, fh, false, upperdentry, stackp);
        kfree(fh);

        if (err) {
                if (err == -ESTALE)
                        return 0;
                return err;
        }

        return 0;
}

/*
 * Verify that @fh matches the file handle stored in xattr @name.
 * Return 0 on match, -ESTALE on mismatch, < 0 on error.
 */
static int ovl_verify_fh(struct ovl_fs *ofs, struct dentry *dentry,
                         enum ovl_xattr ox, const struct ovl_fh *fh)
{
        struct ovl_fh *ofh = ovl_get_fh(ofs, dentry, ox);
        int err = 0;

        if (!ofh)
                return -ENODATA;

        if (IS_ERR(ofh))
                return PTR_ERR(ofh);

        if (fh->fb.len != ofh->fb.len || memcmp(&fh->fb, &ofh->fb, fh->fb.len))
                err = -ESTALE;

        kfree(ofh);
        return err;
}

int ovl_verify_set_fh(struct ovl_fs *ofs, struct dentry *dentry,
                      enum ovl_xattr ox, const struct ovl_fh *fh,
                      bool is_upper, bool set)
{
        int err;

        err = ovl_verify_fh(ofs, dentry, ox, fh);
        if (set && err == -ENODATA)
                err = ovl_setxattr(ofs, dentry, ox, fh->buf, fh->fb.len);

        return err;
}

/*
 * Verify that @real dentry matches the file handle stored in xattr @name.
 *
 * If @set is true and there is no stored file handle, encode @real and store
 * file handle in xattr @name.
 *
 * Return 0 on match, -ESTALE on mismatch, -ENODATA on no xattr, < 0 on error.
 */
int ovl_verify_origin_xattr(struct ovl_fs *ofs, struct dentry *dentry,
                            enum ovl_xattr ox, struct dentry *real,
                            bool is_upper, bool set)
{
        struct inode *inode;
        struct ovl_fh *fh;
        int err;

        fh = ovl_encode_real_fh(ofs, d_inode(real), is_upper);
        err = PTR_ERR(fh);
        if (IS_ERR(fh)) {
                fh = NULL;
                goto fail;
        }

        err = ovl_verify_set_fh(ofs, dentry, ox, fh, is_upper, set);
        if (err)
                goto fail;

out:
        kfree(fh);
        return err;

fail:
        inode = d_inode(real);
        pr_warn_ratelimited("failed to verify %s (%pd2, ino=%lu, err=%i)\n",
                            is_upper ? "upper" : "origin", real,
                            inode ? inode->i_ino : 0, err);
        goto out;
}


/* Get upper dentry from index */
struct dentry *ovl_index_upper(struct ovl_fs *ofs, struct dentry *index,
                               bool connected)
{
        struct ovl_fh *fh;
        struct dentry *upper;

        if (!d_is_dir(index))
                return dget(index);

        fh = ovl_get_fh(ofs, index, OVL_XATTR_UPPER);
        if (IS_ERR_OR_NULL(fh))
                return ERR_CAST(fh);

        upper = ovl_decode_real_fh(ofs, fh, ovl_upper_mnt(ofs), connected);
        kfree(fh);

        if (IS_ERR_OR_NULL(upper))
                return upper ?: ERR_PTR(-ESTALE);

        if (!d_is_dir(upper)) {
                pr_warn_ratelimited("invalid index upper (%pd2, upper=%pd2).\n",
                                    index, upper);
                dput(upper);
                return ERR_PTR(-EIO);
        }

        return upper;
}

/*
 * Verify that an index entry name matches the origin file handle stored in
 * OVL_XATTR_ORIGIN and that origin file handle can be decoded to lower path.
 * Return 0 on match, -ESTALE on mismatch or stale origin, < 0 on error.
 */
int ovl_verify_index(struct ovl_fs *ofs, struct dentry *index)
{
        struct ovl_fh *fh = NULL;
        size_t len;
        struct ovl_path origin = { };
        struct ovl_path *stack = &origin;
        struct dentry *upper = NULL;
        int err;

        if (!d_inode(index))
                return 0;

        err = -EINVAL;
        if (index->d_name.len < sizeof(struct ovl_fb)*2)
                goto fail;

        err = -ENOMEM;
        len = index->d_name.len / 2;
        fh = kzalloc(len + OVL_FH_WIRE_OFFSET, GFP_KERNEL);
        if (!fh)
                goto fail;

        err = -EINVAL;
        if (hex2bin(fh->buf, index->d_name.name, len))
                goto fail;

        err = ovl_check_fb_len(&fh->fb, len);
        if (err)
                goto fail;

        /*
         * Whiteout index entries are used as an indication that an exported
         * overlay file handle should be treated as stale (i.e. after unlink
         * of the overlay inode). These entries contain no origin xattr.
         */
        if (ovl_is_whiteout(index))
                goto out;

        /*
         * Verifying directory index entries are not stale is expensive, so
         * only verify stale dir index if NFS export is enabled.
         */
        if (d_is_dir(index) && !ofs->config.nfs_export)
                goto out;

        /*
         * Directory index entries should have 'upper' xattr pointing to the
         * real upper dir. Non-dir index entries are hardlinks to the upper
         * real inode. For non-dir index, we can read the copy up origin xattr
         * directly from the index dentry, but for dir index we first need to
         * decode the upper directory.
         */
        upper = ovl_index_upper(ofs, index, false);
        if (IS_ERR_OR_NULL(upper)) {
                err = PTR_ERR(upper);
                /*
                 * Directory index entries with no 'upper' xattr need to be
                 * removed. When dir index entry has a stale 'upper' xattr,
                 * we assume that upper dir was removed and we treat the dir
                 * index as orphan entry that needs to be whited out.
                 */
                if (err == -ESTALE)
                        goto orphan;
                else if (!err)
                        err = -ESTALE;
                goto fail;
        }

        err = ovl_verify_fh(ofs, upper, OVL_XATTR_ORIGIN, fh);
        dput(upper);
        if (err)
                goto fail;

        /* Check if non-dir index is orphan and don't warn before cleaning it */
        if (!d_is_dir(index) && d_inode(index)->i_nlink == 1) {
                err = ovl_check_origin_fh(ofs, fh, false, index, &stack);
                if (err)
                        goto fail;

                if (ovl_get_nlink(ofs, origin.dentry, index, 0) == 0)
                        goto orphan;
        }

out:
        dput(origin.dentry);
        kfree(fh);
        return err;

fail:
        pr_warn_ratelimited("failed to verify index (%pd2, ftype=%x, err=%i)\n",
                            index, d_inode(index)->i_mode & S_IFMT, err);
        goto out;

orphan:
        pr_warn_ratelimited("orphan index entry (%pd2, ftype=%x, nlink=%u)\n",
                            index, d_inode(index)->i_mode & S_IFMT,
                            d_inode(index)->i_nlink);
        err = -ENOENT;
        goto out;
}

int ovl_get_index_name_fh(const struct ovl_fh *fh, struct qstr *name)
{
        char *n, *s;

        n = kcalloc(fh->fb.len, 2, GFP_KERNEL);
        if (!n)
                return -ENOMEM;

        s  = bin2hex(n, fh->buf, fh->fb.len);
        *name = (struct qstr) QSTR_INIT(n, s - n);

        return 0;

}

/*
 * Lookup in indexdir for the index entry of a lower real inode or a copy up
 * origin inode. The index entry name is the hex representation of the lower
 * inode file handle.
 *
 * If the index dentry in negative, then either no lower aliases have been
 * copied up yet, or aliases have been copied up in older kernels and are
 * not indexed.
 *
 * If the index dentry for a copy up origin inode is positive, but points
 * to an inode different than the upper inode, then either the upper inode
 * has been copied up and not indexed or it was indexed, but since then
 * index dir was cleared. Either way, that index cannot be used to identify
 * the overlay inode.
 */
int ovl_get_index_name(struct ovl_fs *ofs, struct dentry *origin,
                       struct qstr *name)
{
        struct ovl_fh *fh;
        int err;

        fh = ovl_encode_real_fh(ofs, d_inode(origin), false);
        if (IS_ERR(fh))
                return PTR_ERR(fh);

        err = ovl_get_index_name_fh(fh, name);

        kfree(fh);
        return err;
}

/* Lookup index by file handle for NFS export */
struct dentry *ovl_get_index_fh(struct ovl_fs *ofs, struct ovl_fh *fh)
{
        struct dentry *index;
        struct qstr name;
        int err;

        err = ovl_get_index_name_fh(fh, &name);
        if (err)
                return ERR_PTR(err);

        index = lookup_noperm_positive_unlocked(&name, ofs->workdir);
        kfree(name.name);
        if (IS_ERR(index)) {
                if (PTR_ERR(index) == -ENOENT)
                        index = NULL;
                return index;
        }

        if (ovl_is_whiteout(index))
                err = -ESTALE;
        else if (ovl_dentry_weird(index))
                err = -EIO;
        else
                return index;

        dput(index);
        return ERR_PTR(err);
}

struct dentry *ovl_lookup_index(struct ovl_fs *ofs, struct dentry *upper,
                                struct dentry *origin, bool verify)
{
        struct dentry *index;
        struct inode *inode;
        struct qstr name;
        bool is_dir = d_is_dir(origin);
        int err;

        err = ovl_get_index_name(ofs, origin, &name);
        if (err)
                return ERR_PTR(err);

        index = lookup_one_positive_unlocked(ovl_upper_mnt_idmap(ofs), &name,
                                             ofs->workdir);
        if (IS_ERR(index)) {
                err = PTR_ERR(index);
                if (err == -ENOENT) {
                        index = NULL;
                        goto out;
                }
                pr_warn_ratelimited("failed inode index lookup (ino=%lu, key=%.*s, err=%i);\n"
                                    "overlayfs: mount with '-o index=off' to disable inodes index.\n",
                                    d_inode(origin)->i_ino, name.len, name.name,
                                    err);
                goto out;
        }

        inode = d_inode(index);
        if (ovl_is_whiteout(index) && !verify) {
                /*
                 * When index lookup is called with !verify for decoding an
                 * overlay file handle, a whiteout index implies that decode
                 * should treat file handle as stale and no need to print a
                 * warning about it.
                 */
                dput(index);
                index = ERR_PTR(-ESTALE);
                goto out;
        } else if (ovl_dentry_weird(index) || ovl_is_whiteout(index) ||
                   inode_wrong_type(inode, d_inode(origin)->i_mode)) {
                /*
                 * Index should always be of the same file type as origin
                 * except for the case of a whiteout index. A whiteout
                 * index should only exist if all lower aliases have been
                 * unlinked, which means that finding a lower origin on lookup
                 * whose index is a whiteout should be treated as an error.
                 */
                pr_warn_ratelimited("bad index found (index=%pd2, ftype=%x, origin ftype=%x).\n",
                                    index, d_inode(index)->i_mode & S_IFMT,
                                    d_inode(origin)->i_mode & S_IFMT);
                goto fail;
        } else if (is_dir && verify) {
                if (!upper) {
                        pr_warn_ratelimited("suspected uncovered redirected dir found (origin=%pd2, index=%pd2).\n",
                                            origin, index);
                        goto fail;
                }

                /* Verify that dir index 'upper' xattr points to upper dir */
                err = ovl_verify_upper(ofs, index, upper, false);
                if (err) {
                        if (err == -ESTALE) {
                                pr_warn_ratelimited("suspected multiply redirected dir found (upper=%pd2, origin=%pd2, index=%pd2).\n",
                                                    upper, origin, index);
                        }
                        goto fail;
                }
        } else if (upper && d_inode(upper) != inode) {
                goto out_dput;
        }
out:
        kfree(name.name);
        return index;

out_dput:
        dput(index);
        index = NULL;
        goto out;

fail:
        dput(index);
        index = ERR_PTR(-EIO);
        goto out;
}

/*
 * Returns next layer in stack starting from top.
 * Returns -1 if this is the last layer.
 */
int ovl_path_next(int idx, struct dentry *dentry, struct path *path,
                  const struct ovl_layer **layer)
{
        struct ovl_entry *oe = OVL_E(dentry);
        struct ovl_path *lowerstack = ovl_lowerstack(oe);

        BUG_ON(idx < 0);
        if (idx == 0) {
                ovl_path_upper(dentry, path);
                if (path->dentry) {
                        *layer = &OVL_FS(dentry->d_sb)->layers[0];
                        return ovl_numlower(oe) ? 1 : -1;
                }
                idx++;
        }
        BUG_ON(idx > ovl_numlower(oe));
        path->dentry = lowerstack[idx - 1].dentry;
        *layer = lowerstack[idx - 1].layer;
        path->mnt = (*layer)->mnt;

        return (idx < ovl_numlower(oe)) ? idx + 1 : -1;
}

/* Fix missing 'origin' xattr */
static int ovl_fix_origin(struct ovl_fs *ofs, struct dentry *dentry,
                          struct dentry *lower, struct dentry *upper)
{
        const struct ovl_fh *fh;
        int err;

        if (ovl_check_origin_xattr(ofs, upper))
                return 0;

        fh = ovl_get_origin_fh(ofs, lower);
        if (IS_ERR(fh))
                return PTR_ERR(fh);

        err = ovl_want_write(dentry);
        if (err)
                goto out;

        err = ovl_set_origin_fh(ofs, fh, upper);
        if (!err)
                err = ovl_set_impure(dentry->d_parent, upper->d_parent);

        ovl_drop_write(dentry);
out:
        kfree(fh);
        return err;
}

static int ovl_maybe_validate_verity(struct dentry *dentry)
{
        struct ovl_fs *ofs = OVL_FS(dentry->d_sb);
        struct inode *inode = d_inode(dentry);
        struct path datapath, metapath;
        int err;

        if (!ofs->config.verity_mode ||
            !ovl_is_metacopy_dentry(dentry) ||
            ovl_test_flag(OVL_VERIFIED_DIGEST, inode))
                return 0;

        if (!ovl_test_flag(OVL_HAS_DIGEST, inode)) {
                if (ofs->config.verity_mode == OVL_VERITY_REQUIRE) {
                        pr_warn_ratelimited("metacopy file '%pd' has no digest specified\n",
                                            dentry);
                        return -EIO;
                }
                return 0;
        }

        ovl_path_lowerdata(dentry, &datapath);
        if (!datapath.dentry)
                return -EIO;

        ovl_path_real(dentry, &metapath);
        if (!metapath.dentry)
                return -EIO;

        err = ovl_inode_lock_interruptible(inode);
        if (err)
                return err;

        if (!ovl_test_flag(OVL_VERIFIED_DIGEST, inode)) {
                with_ovl_creds(dentry->d_sb)
                        err = ovl_validate_verity(ofs, &metapath, &datapath);
                if (err == 0)
                        ovl_set_flag(OVL_VERIFIED_DIGEST, inode);
        }

        ovl_inode_unlock(inode);

        return err;
}

/* Lazy lookup of lowerdata */
static int ovl_maybe_lookup_lowerdata(struct dentry *dentry)
{
        struct inode *inode = d_inode(dentry);
        const char *redirect = ovl_lowerdata_redirect(inode);
        struct ovl_path datapath = {};
        int err;

        if (!redirect || ovl_dentry_lowerdata(dentry))
                return 0;

        if (redirect[0] != '/')
                return -EIO;

        err = ovl_inode_lock_interruptible(inode);
        if (err)
                return err;

        err = 0;
        /* Someone got here before us? */
        if (ovl_dentry_lowerdata(dentry))
                goto out;

        with_ovl_creds(dentry->d_sb)
                err = ovl_lookup_data_layers(dentry, redirect, &datapath);
        if (err)
                goto out_err;

        err = ovl_dentry_set_lowerdata(dentry, &datapath);
        if (err)
                goto out_err;

out:
        ovl_inode_unlock(inode);
        dput(datapath.dentry);

        return err;

out_err:
        pr_warn_ratelimited("lazy lowerdata lookup failed (%pd2, err=%i)\n",
                            dentry, err);
        goto out;
}

int ovl_verify_lowerdata(struct dentry *dentry)
{
        int err;

        err = ovl_maybe_lookup_lowerdata(dentry);
        if (err)
                return err;

        return ovl_maybe_validate_verity(dentry);
}

/*
 * Following redirects/metacopy can have security consequences: it's like a
 * symlink into the lower layer without the permission checks.
 *
 * This is only a problem if the upper layer is untrusted (e.g comes from an USB
 * drive).  This can allow a non-readable file or directory to become readable.
 *
 * Only following redirects when redirects are enabled disables this attack
 * vector when not necessary.
 */
static bool ovl_check_follow_redirect(struct ovl_lookup_data *d)
{
        struct ovl_fs *ofs = OVL_FS(d->sb);

        if (d->metacopy && !ofs->config.metacopy) {
                pr_warn_ratelimited("refusing to follow metacopy origin for (%pd2)\n", d->dentry);
                return false;
        }
        if ((d->redirect || d->upperredirect) && !ovl_redirect_follow(ofs)) {
                pr_warn_ratelimited("refusing to follow redirect for (%pd2)\n", d->dentry);
                return false;
        }
        return true;
}

struct ovl_lookup_ctx {
        struct dentry *dentry;
        struct ovl_entry *oe;
        struct ovl_path *stack;
        struct ovl_path *origin_path;
        struct dentry *upperdentry;
        struct dentry *index;
        struct inode *inode;
        unsigned int ctr;
};

static int ovl_lookup_layers(struct ovl_lookup_ctx *ctx, struct ovl_lookup_data *d)
{
        struct dentry *dentry = ctx->dentry;
        struct ovl_fs *ofs = OVL_FS(dentry->d_sb);
        struct ovl_entry *poe = OVL_E(dentry->d_parent);
        struct ovl_entry *roe = OVL_E(dentry->d_sb->s_root);
        bool check_redirect = (ovl_redirect_follow(ofs) || ofs->numdatalayer);
        struct dentry *upperdir;
        struct dentry *this;
        struct dentry *origin = NULL;
        bool upperopaque = false;
        bool uppermetacopy = false;
        int metacopy_size = 0;
        unsigned int i;
        int err;

        upperdir = ovl_dentry_upper(dentry->d_parent);
        if (upperdir) {
                d->layer = &ofs->layers[0];
                err = ovl_lookup_layer(upperdir, d, &ctx->upperdentry, true);
                if (err)
                        return err;

                if (ctx->upperdentry && ctx->upperdentry->d_flags & DCACHE_OP_REAL)
                        return -EREMOTE;

                if (ctx->upperdentry && !d->is_dir) {
                        /*
                         * Lookup copy up origin by decoding origin file handle.
                         * We may get a disconnected dentry, which is fine,
                         * because we only need to hold the origin inode in
                         * cache and use its inode number.  We may even get a
                         * connected dentry, that is not under any of the lower
                         * layers root.  That is also fine for using it's inode
                         * number - it's the same as if we held a reference
                         * to a dentry in lower layer that was moved under us.
                         */
                        err = ovl_check_origin(ofs, ctx->upperdentry, &ctx->origin_path);
                        if (err)
                                return err;

                        if (d->metacopy)
                                uppermetacopy = true;
                        metacopy_size = d->metacopy;
                }

                if (d->redirect) {
                        err = -ENOMEM;
                        d->upperredirect = kstrdup(d->redirect, GFP_KERNEL);
                        if (!d->upperredirect)
                                return err;
                        if (d->redirect[0] == '/')
                                poe = roe;
                }
                upperopaque = d->opaque;
        }

        if (!d->stop && ovl_numlower(poe)) {
                err = -ENOMEM;
                ctx->stack = ovl_stack_alloc(ofs->numlayer - 1);
                if (!ctx->stack)
                        return err;
        }

        for (i = 0; !d->stop && i < ovl_numlower(poe); i++) {
                struct ovl_path lower = ovl_lowerstack(poe)[i];

                if (!ovl_check_follow_redirect(d)) {
                        err = -EPERM;
                        return err;
                }

                if (!check_redirect)
                        d->last = i == ovl_numlower(poe) - 1;
                else if (d->is_dir || !ofs->numdatalayer)
                        d->last = lower.layer->idx == ovl_numlower(roe);

                d->layer = lower.layer;
                err = ovl_lookup_layer(lower.dentry, d, &this, false);
                if (err)
                        return err;

                if (!this)
                        continue;

                /*
                 * If no origin fh is stored in upper of a merge dir, store fh
                 * of lower dir and set upper parent "impure".
                 */
                if (ctx->upperdentry && !ctx->ctr && !ofs->noxattr && d->is_dir) {
                        err = ovl_fix_origin(ofs, dentry, this, ctx->upperdentry);
                        if (err) {
                                dput(this);
                                return err;
                        }
                }

                /*
                 * When "verify_lower" feature is enabled, do not merge with a
                 * lower dir that does not match a stored origin xattr. In any
                 * case, only verified origin is used for index lookup.
                 *
                 * For non-dir dentry, if index=on, then ensure origin
                 * matches the dentry found using path based lookup,
                 * otherwise error out.
                 */
                if (ctx->upperdentry && !ctx->ctr &&
                    ((d->is_dir && ovl_verify_lower(dentry->d_sb)) ||
                     (!d->is_dir && ofs->config.index && ctx->origin_path))) {
                        err = ovl_verify_origin(ofs, ctx->upperdentry, this, false);
                        if (err) {
                                dput(this);
                                if (d->is_dir)
                                        break;
                                return err;
                        }
                        origin = this;
                }

                if (!ctx->upperdentry && !d->is_dir && !ctx->ctr && d->metacopy)
                        metacopy_size = d->metacopy;

                if (d->metacopy && ctx->ctr) {
                        /*
                         * Do not store intermediate metacopy dentries in
                         * lower chain, except top most lower metacopy dentry.
                         * Continue the loop so that if there is an absolute
                         * redirect on this dentry, poe can be reset to roe.
                         */
                        dput(this);
                        this = NULL;
                } else {
                        ctx->stack[ctx->ctr].dentry = this;
                        ctx->stack[ctx->ctr].layer = lower.layer;
                        ctx->ctr++;
                }

                if (d->stop)
                        break;

                if (d->redirect && d->redirect[0] == '/' && poe != roe) {
                        poe = roe;
                        /* Find the current layer on the root dentry */
                        i = lower.layer->idx - 1;
                }
        }

        /*
         * Defer lookup of lowerdata in data-only layers to first access.
         * Don't require redirect=follow and metacopy=on in this case.
         */
        if (d->metacopy && ctx->ctr && ofs->numdatalayer && d->absolute_redirect) {
                d->metacopy = 0;
                ctx->ctr++;
        } else if (!ovl_check_follow_redirect(d)) {
                err = -EPERM;
                return err;
        }

        /*
         * For regular non-metacopy upper dentries, there is no lower
         * path based lookup, hence ctr will be zero. If a dentry is found
         * using ORIGIN xattr on upper, install it in stack.
         *
         * For metacopy dentry, path based lookup will find lower dentries.
         * Just make sure a corresponding data dentry has been found.
         */
        if (d->metacopy || (uppermetacopy && !ctx->ctr)) {
                pr_warn_ratelimited("metacopy with no lower data found - abort lookup (%pd2)\n",
                                    dentry);
                err = -EIO;
                return err;
        } else if (!d->is_dir && ctx->upperdentry && !ctx->ctr && ctx->origin_path) {
                if (WARN_ON(ctx->stack != NULL)) {
                        err = -EIO;
                        return err;
                }
                ctx->stack = ctx->origin_path;
                ctx->ctr = 1;
                origin = ctx->origin_path->dentry;
                ctx->origin_path = NULL;
        }

        /*
         * Always lookup index if there is no-upperdentry.
         *
         * For the case of upperdentry, we have set origin by now if it
         * needed to be set. There are basically three cases.
         *
         * For directories, lookup index by lower inode and verify it matches
         * upper inode. We only trust dir index if we verified that lower dir
         * matches origin, otherwise dir index entries may be inconsistent
         * and we ignore them.
         *
         * For regular upper, we already set origin if upper had ORIGIN
         * xattr. There is no verification though as there is no path
         * based dentry lookup in lower in this case.
         *
         * For metacopy upper, we set a verified origin already if index
         * is enabled and if upper had an ORIGIN xattr.
         *
         */
        if (!ctx->upperdentry && ctx->ctr)
                origin = ctx->stack[0].dentry;

        if (origin && ovl_indexdir(dentry->d_sb) &&
            (!d->is_dir || ovl_index_all(dentry->d_sb))) {
                ctx->index = ovl_lookup_index(ofs, ctx->upperdentry, origin, true);
                if (IS_ERR(ctx->index)) {
                        err = PTR_ERR(ctx->index);
                        ctx->index = NULL;
                        return err;
                }
        }

        if (ctx->ctr) {
                ctx->oe = ovl_alloc_entry(ctx->ctr);
                err = -ENOMEM;
                if (!ctx->oe)
                        return err;

                ovl_stack_cpy(ovl_lowerstack(ctx->oe), ctx->stack, ctx->ctr);
        }

        if (upperopaque)
                ovl_dentry_set_opaque(dentry);
        if (d->xwhiteouts)
                ovl_dentry_set_xwhiteouts(dentry);

        if (ctx->upperdentry)
                ovl_dentry_set_upper_alias(dentry);
        else if (ctx->index) {
                char *upperredirect;
                struct path upperpath = {
                        .dentry = ctx->upperdentry = dget(ctx->index),
                        .mnt = ovl_upper_mnt(ofs),
                };

                /*
                 * It's safe to assign upperredirect here: the previous
                 * assignment happens only if upperdentry is non-NULL, and
                 * this one only if upperdentry is NULL.
                 */
                upperredirect = ovl_get_redirect_xattr(ofs, &upperpath, 0);
                if (IS_ERR(upperredirect))
                        return PTR_ERR(upperredirect);
                d->upperredirect = upperredirect;

                err = ovl_check_metacopy_xattr(ofs, &upperpath, NULL);
                if (err < 0)
                        return err;
                d->metacopy = uppermetacopy = err;
                metacopy_size = err;

                if (!ovl_check_follow_redirect(d)) {
                        err = -EPERM;
                        return err;
                }
        }

        if (ctx->upperdentry || ctx->ctr) {
                struct inode *inode;
                struct ovl_inode_params oip = {
                        .upperdentry = ctx->upperdentry,
                        .oe = ctx->oe,
                        .index = ctx->index,
                        .redirect = d->upperredirect,
                };

                /* Store lowerdata redirect for lazy lookup */
                if (ctx->ctr > 1 && !d->is_dir && !ctx->stack[ctx->ctr - 1].dentry) {
                        oip.lowerdata_redirect = d->redirect;
                        d->redirect = NULL;
                }

                inode = ovl_get_inode(dentry->d_sb, &oip);
                if (IS_ERR(inode))
                        return PTR_ERR(inode);

                ctx->inode = inode;
                if (ctx->upperdentry && !uppermetacopy)
                        ovl_set_flag(OVL_UPPERDATA, ctx->inode);

                if (metacopy_size > OVL_METACOPY_MIN_SIZE)
                        ovl_set_flag(OVL_HAS_DIGEST, ctx->inode);
        }

        ovl_dentry_init_reval(dentry, ctx->upperdentry, OVL_I_E(ctx->inode));

        return 0;
}

struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
                          unsigned int flags)
{
        struct ovl_fs *ofs = OVL_FS(dentry->d_sb);
        struct ovl_entry *poe = OVL_E(dentry->d_parent);
        bool check_redirect = (ovl_redirect_follow(ofs) || ofs->numdatalayer);
        int err;
        struct ovl_lookup_ctx ctx = {
                .dentry = dentry,
        };
        struct ovl_lookup_data d = {
                .sb     = dentry->d_sb,
                .dentry = dentry,
                .name   = dentry->d_name,
                .last   = check_redirect ? false : !ovl_numlower(poe),
        };

        if (dentry->d_name.len > ofs->namelen)
                return ERR_PTR(-ENAMETOOLONG);

        with_ovl_creds(dentry->d_sb)
                err = ovl_lookup_layers(&ctx, &d);

        if (ctx.origin_path) {
                dput(ctx.origin_path->dentry);
                kfree(ctx.origin_path);
        }
        dput(ctx.index);
        ovl_stack_free(ctx.stack, ctx.ctr);
        kfree(d.redirect);

        if (err) {
                ovl_free_entry(ctx.oe);
                dput(ctx.upperdentry);
                kfree(d.upperredirect);
                return ERR_PTR(err);
        }

        return d_splice_alias(ctx.inode, dentry);
}

bool ovl_lower_positive(struct dentry *dentry)
{
        struct ovl_entry *poe = OVL_E(dentry->d_parent);
        const struct qstr *name = &dentry->d_name;
        unsigned int i;
        bool positive = false;
        bool done = false;

        /*
         * If dentry is negative, then lower is positive iff this is a
         * whiteout.
         */
        if (!dentry->d_inode)
                return ovl_dentry_is_opaque(dentry);

        /* Negative upper -> positive lower */
        if (!ovl_dentry_upper(dentry))
                return true;

        with_ovl_creds(dentry->d_sb) {
                /* Positive upper -> have to look up lower to see whether it exists */
                for (i = 0; !done && !positive && i < ovl_numlower(poe); i++) {
                        struct dentry *this;
                        struct ovl_path *parentpath = &ovl_lowerstack(poe)[i];

                        /*
                         * We need to make a non-const copy of dentry->d_name,
                         * because lookup_one_positive_unlocked() will hash name
                         * with parentpath base, which is on another (lower fs).
                         */
                        this = lookup_one_positive_unlocked(mnt_idmap(parentpath->layer->mnt),
                                                            &QSTR_LEN(name->name, name->len),
                                                            parentpath->dentry);
                        if (IS_ERR(this)) {
                                switch (PTR_ERR(this)) {
                                case -ENOENT:
                                case -ENAMETOOLONG:
                                        break;

                                default:
                                        /*
                                         * Assume something is there, we just couldn't
                                         * access it.
                                         */
                                        positive = true;
                                        break;
                                }
                        } else {
                                struct path path = {
                                        .dentry = this,
                                        .mnt    = parentpath->layer->mnt,
                                };
                                positive = !ovl_path_is_whiteout(OVL_FS(dentry->d_sb), &path);
                                done = true;
                                dput(this);
                        }
                }
        }

        return positive;
}