// SPDX-License-Identifier: GPL-2.0-only
/*
 * Copyright (C) 2017 Red Hat, Inc.
 */

#include <linux/cred.h>
#include <linux/file.h>
#include <linux/filelock.h>
#include <linux/mount.h>
#include <linux/xattr.h>
#include <linux/uio.h>
#include <linux/uaccess.h>
#include <linux/security.h>
#include <linux/fs.h>
#include <linux/backing-file.h>
#include "overlayfs.h"

static char ovl_whatisit(struct inode *inode, struct inode *realinode)
{
        if (realinode != ovl_inode_upper(inode))
                return 'l';
        if (ovl_has_upperdata(inode))
                return 'u';
        else
                return 'm';
}

static struct file *ovl_open_realfile(const struct file *file,
                                      const struct path *realpath)
{
        struct inode *realinode = d_inode(realpath->dentry);
        struct inode *inode = file_inode(file);
        struct mnt_idmap *real_idmap;
        struct file *realfile;
        int flags = file->f_flags | OVL_OPEN_FLAGS;
        int acc_mode = ACC_MODE(flags);
        int err;

        if (flags & O_APPEND)
                acc_mode |= MAY_APPEND;

        with_ovl_creds(inode->i_sb) {
                real_idmap = mnt_idmap(realpath->mnt);
                err = inode_permission(real_idmap, realinode, MAY_OPEN | acc_mode);
                if (err) {
                        realfile = ERR_PTR(err);
                } else {
                        if (!inode_owner_or_capable(real_idmap, realinode))
                                flags &= ~O_NOATIME;

                        realfile = backing_file_open(file_user_path(file),
                                                     flags, realpath, current_cred());
                }
        }

        pr_debug("open(%p[%pD2/%c], 0%o) -> (%p, 0%o)\n",
                 file, file, ovl_whatisit(inode, realinode), file->f_flags,
                 realfile, IS_ERR(realfile) ? 0 : realfile->f_flags);

        return realfile;
}

#define OVL_SETFL_MASK (O_APPEND | O_NONBLOCK | O_NDELAY | O_DIRECT)

static int ovl_change_flags(struct file *file, unsigned int flags)
{
        struct inode *inode = file_inode(file);
        int err;

        flags &= OVL_SETFL_MASK;

        if (((flags ^ file->f_flags) & O_APPEND) && IS_APPEND(inode))
                return -EPERM;

        if ((flags & O_DIRECT) && !(file->f_mode & FMODE_CAN_ODIRECT))
                return -EINVAL;

        if (file->f_op->check_flags) {
                err = file->f_op->check_flags(flags);
                if (err)
                        return err;
        }

        spin_lock(&file->f_lock);
        file->f_flags = (file->f_flags & ~OVL_SETFL_MASK) | flags;
        file->f_iocb_flags = iocb_flags(file);
        spin_unlock(&file->f_lock);

        return 0;
}

struct ovl_file {
        struct file *realfile;
        struct file *upperfile;
};

struct ovl_file *ovl_file_alloc(struct file *realfile)
{
        struct ovl_file *of = kzalloc_obj(struct ovl_file);

        if (unlikely(!of))
                return NULL;

        of->realfile = realfile;
        return of;
}

void ovl_file_free(struct ovl_file *of)
{
        fput(of->realfile);
        if (of->upperfile)
                fput(of->upperfile);
        kfree(of);
}

static bool ovl_is_real_file(const struct file *realfile,
                             const struct path *realpath)
{
        return file_inode(realfile) == d_inode(realpath->dentry);
}

static struct file *ovl_real_file_path(const struct file *file,
                                       const struct path *realpath)
{
        struct ovl_file *of = file->private_data;
        struct file *realfile = of->realfile;

        if (WARN_ON_ONCE(!realpath->dentry))
                return ERR_PTR(-EIO);

        /*
         * If the realfile that we want is not where the data used to be at
         * open time, either we'd been copied up, or it's an fsync of a
         * metacopied file.  We need the upperfile either way, so see if it
         * is already opened and if it is not then open and store it.
         */
        if (unlikely(!ovl_is_real_file(realfile, realpath))) {
                struct file *upperfile = READ_ONCE(of->upperfile);
                struct file *old;

                if (!upperfile) { /* Nobody opened upperfile yet */
                        upperfile = ovl_open_realfile(file, realpath);
                        if (IS_ERR(upperfile))
                                return upperfile;

                        /* Store the upperfile for later */
                        old = cmpxchg_release(&of->upperfile, NULL, upperfile);
                        if (old) { /* Someone opened upperfile before us */
                                fput(upperfile);
                                upperfile = old;
                        }
                }
                /*
                 * Stored file must be from the right inode, unless someone's
                 * been corrupting the upper layer.
                 */
                if (WARN_ON_ONCE(!ovl_is_real_file(upperfile, realpath)))
                        return ERR_PTR(-EIO);

                realfile = upperfile;
        }

        /* Did the flags change since open? */
        if (unlikely((file->f_flags ^ realfile->f_flags) & ~OVL_OPEN_FLAGS)) {
                int err = ovl_change_flags(realfile, file->f_flags);

                if (err)
                        return ERR_PTR(err);
        }

        return realfile;
}

static struct file *ovl_real_file(const struct file *file)
{
        struct dentry *dentry = file_dentry(file);
        struct path realpath;
        int err;

        if (d_is_dir(dentry)) {
                struct file *f = ovl_dir_real_file(file, false);

                if (WARN_ON_ONCE(!f))
                        return ERR_PTR(-EIO);
                return f;
        }

        /* lazy lookup and verify of lowerdata */
        err = ovl_verify_lowerdata(dentry);
        if (err)
                return ERR_PTR(err);

        ovl_path_realdata(dentry, &realpath);

        return ovl_real_file_path(file, &realpath);
}

static int ovl_open(struct inode *inode, struct file *file)
{
        struct dentry *dentry = file_dentry(file);
        struct file *realfile;
        struct path realpath;
        struct ovl_file *of;
        int err;

        /* lazy lookup and verify lowerdata */
        err = ovl_verify_lowerdata(dentry);
        if (err)
                return err;

        err = ovl_maybe_copy_up(dentry, file->f_flags);
        if (err)
                return err;

        /* No longer need these flags, so don't pass them on to underlying fs */
        file->f_flags &= ~(O_CREAT | O_EXCL | O_NOCTTY | O_TRUNC);

        ovl_path_realdata(dentry, &realpath);
        if (!realpath.dentry)
                return -EIO;

        realfile = ovl_open_realfile(file, &realpath);
        if (IS_ERR(realfile))
                return PTR_ERR(realfile);

        of = ovl_file_alloc(realfile);
        if (!of) {
                fput(realfile);
                return -ENOMEM;
        }

        file->private_data = of;

        return 0;
}

static int ovl_release(struct inode *inode, struct file *file)
{
        ovl_file_free(file->private_data);
        return 0;
}

static loff_t ovl_llseek(struct file *file, loff_t offset, int whence)
{
        struct inode *inode = file_inode(file);
        struct file *realfile;
        loff_t ret;

        /*
         * The two special cases below do not need to involve real fs,
         * so we can optimizing concurrent callers.
         */
        if (offset == 0) {
                if (whence == SEEK_CUR)
                        return file->f_pos;

                if (whence == SEEK_SET)
                        return vfs_setpos(file, 0, 0);
        }

        realfile = ovl_real_file(file);
        if (IS_ERR(realfile))
                return PTR_ERR(realfile);

        /*
         * Overlay file f_pos is the master copy that is preserved
         * through copy up and modified on read/write, but only real
         * fs knows how to SEEK_HOLE/SEEK_DATA and real fs may impose
         * limitations that are more strict than ->s_maxbytes for specific
         * files, so we use the real file to perform seeks.
         */
        ovl_inode_lock(inode);
        realfile->f_pos = file->f_pos;

        with_ovl_creds(inode->i_sb)
                ret = vfs_llseek(realfile, offset, whence);

        file->f_pos = realfile->f_pos;
        ovl_inode_unlock(inode);

        return ret;
}

static void ovl_file_modified(struct file *file)
{
        /* Update size/mtime */
        ovl_copyattr(file_inode(file));
}

static void ovl_file_end_write(struct kiocb *iocb, ssize_t ret)
{
        ovl_file_modified(iocb->ki_filp);
}

static void ovl_file_accessed(struct file *file)
{
        struct inode *inode, *upperinode;
        struct timespec64 ctime, uctime;
        struct timespec64 mtime, umtime;

        if (file->f_flags & O_NOATIME)
                return;

        inode = file_inode(file);
        upperinode = ovl_inode_upper(inode);

        if (!upperinode)
                return;

        ctime = inode_get_ctime(inode);
        uctime = inode_get_ctime(upperinode);
        mtime = inode_get_mtime(inode);
        umtime = inode_get_mtime(upperinode);
        if ((!timespec64_equal(&mtime, &umtime)) ||
             !timespec64_equal(&ctime, &uctime)) {
                inode_set_mtime_to_ts(inode, inode_get_mtime(upperinode));
                inode_set_ctime_to_ts(inode, uctime);
        }

        touch_atime(&file->f_path);
}

static ssize_t ovl_read_iter(struct kiocb *iocb, struct iov_iter *iter)
{
        struct file *file = iocb->ki_filp;
        struct file *realfile;
        struct backing_file_ctx ctx = {
                .cred = ovl_creds(file_inode(file)->i_sb),
                .accessed = ovl_file_accessed,
        };

        if (!iov_iter_count(iter))
                return 0;

        realfile = ovl_real_file(file);
        if (IS_ERR(realfile))
                return PTR_ERR(realfile);

        return backing_file_read_iter(realfile, iter, iocb, iocb->ki_flags,
                                      &ctx);
}

static ssize_t ovl_write_iter(struct kiocb *iocb, struct iov_iter *iter)
{
        struct file *file = iocb->ki_filp;
        struct inode *inode = file_inode(file);
        struct file *realfile;
        ssize_t ret;
        int ifl = iocb->ki_flags;
        struct backing_file_ctx ctx = {
                .cred = ovl_creds(inode->i_sb),
                .end_write = ovl_file_end_write,
        };

        if (!iov_iter_count(iter))
                return 0;

        inode_lock(inode);
        /* Update mode */
        ovl_copyattr(inode);

        realfile = ovl_real_file(file);
        ret = PTR_ERR(realfile);
        if (IS_ERR(realfile))
                goto out_unlock;

        if (!ovl_should_sync(OVL_FS(inode->i_sb)))
                ifl &= ~(IOCB_DSYNC | IOCB_SYNC);

        ret = backing_file_write_iter(realfile, iter, iocb, ifl, &ctx);

out_unlock:
        inode_unlock(inode);

        return ret;
}

static ssize_t ovl_splice_read(struct file *in, loff_t *ppos,
                               struct pipe_inode_info *pipe, size_t len,
                               unsigned int flags)
{
        struct file *realfile;
        ssize_t ret;
        struct backing_file_ctx ctx = {
                .cred = ovl_creds(file_inode(in)->i_sb),
                .accessed = ovl_file_accessed,
        };
        struct kiocb iocb;

        realfile = ovl_real_file(in);
        if (IS_ERR(realfile))
                return PTR_ERR(realfile);

        init_sync_kiocb(&iocb, in);
        iocb.ki_pos = *ppos;
        ret = backing_file_splice_read(realfile, &iocb, pipe, len, flags, &ctx);
        *ppos = iocb.ki_pos;

        return ret;
}

/*
 * Calling iter_file_splice_write() directly from overlay's f_op may deadlock
 * due to lock order inversion between pipe->mutex in iter_file_splice_write()
 * and file_start_write(realfile) in ovl_write_iter().
 *
 * So do everything ovl_write_iter() does and call iter_file_splice_write() on
 * the real file.
 */
static ssize_t ovl_splice_write(struct pipe_inode_info *pipe, struct file *out,
                                loff_t *ppos, size_t len, unsigned int flags)
{
        struct file *realfile;
        struct inode *inode = file_inode(out);
        ssize_t ret;
        struct backing_file_ctx ctx = {
                .cred = ovl_creds(inode->i_sb),
                .end_write = ovl_file_end_write,
        };
        struct kiocb iocb;

        inode_lock(inode);
        /* Update mode */
        ovl_copyattr(inode);

        realfile = ovl_real_file(out);
        ret = PTR_ERR(realfile);
        if (IS_ERR(realfile))
                goto out_unlock;

        init_sync_kiocb(&iocb, out);
        iocb.ki_pos = *ppos;
        ret = backing_file_splice_write(pipe, realfile, &iocb, len, flags, &ctx);
        *ppos = iocb.ki_pos;

out_unlock:
        inode_unlock(inode);

        return ret;
}

static int ovl_fsync(struct file *file, loff_t start, loff_t end, int datasync)
{
        struct dentry *dentry = file_dentry(file);
        enum ovl_path_type type;
        struct path upperpath;
        struct file *upperfile;
        int ret;

        ret = ovl_sync_status(OVL_FS(file_inode(file)->i_sb));
        if (ret <= 0)
                return ret;

        /* Don't sync lower file for fear of receiving EROFS error */
        type = ovl_path_type(dentry);
        if (!OVL_TYPE_UPPER(type) || (datasync && OVL_TYPE_MERGE(type)))
                return 0;

        ovl_path_upper(dentry, &upperpath);
        upperfile = ovl_real_file_path(file, &upperpath);
        if (IS_ERR(upperfile))
                return PTR_ERR(upperfile);

        with_ovl_creds(file_inode(file)->i_sb)
                return vfs_fsync_range(upperfile, start, end, datasync);
}

static int ovl_mmap(struct file *file, struct vm_area_struct *vma)
{
        struct ovl_file *of = file->private_data;
        struct backing_file_ctx ctx = {
                .cred = ovl_creds(file_inode(file)->i_sb),
                .accessed = ovl_file_accessed,
        };

        return backing_file_mmap(of->realfile, vma, &ctx);
}

static long ovl_fallocate(struct file *file, int mode, loff_t offset, loff_t len)
{
        struct inode *inode = file_inode(file);
        struct file *realfile;
        int ret;

        inode_lock(inode);
        /* Update mode */
        ovl_copyattr(inode);
        ret = file_remove_privs(file);
        if (ret)
                goto out_unlock;

        realfile = ovl_real_file(file);
        ret = PTR_ERR(realfile);
        if (IS_ERR(realfile))
                goto out_unlock;

        with_ovl_creds(inode->i_sb)
                ret = vfs_fallocate(realfile, mode, offset, len);

        /* Update size */
        ovl_file_modified(file);

out_unlock:
        inode_unlock(inode);

        return ret;
}

static int ovl_fadvise(struct file *file, loff_t offset, loff_t len, int advice)
{
        struct file *realfile;

        realfile = ovl_real_file(file);
        if (IS_ERR(realfile))
                return PTR_ERR(realfile);

        with_ovl_creds(file_inode(file)->i_sb)
                return vfs_fadvise(realfile, offset, len, advice);
}

enum ovl_copyop {
        OVL_COPY,
        OVL_CLONE,
        OVL_DEDUPE,
};

static loff_t ovl_copyfile(struct file *file_in, loff_t pos_in,
                            struct file *file_out, loff_t pos_out,
                            loff_t len, unsigned int flags, enum ovl_copyop op)
{
        struct inode *inode_out = file_inode(file_out);
        struct file *realfile_in, *realfile_out;
        loff_t ret;

        inode_lock(inode_out);
        if (op != OVL_DEDUPE) {
                /* Update mode */
                ovl_copyattr(inode_out);
                ret = file_remove_privs(file_out);
                if (ret)
                        goto out_unlock;
        }

        realfile_out = ovl_real_file(file_out);
        ret = PTR_ERR(realfile_out);
        if (IS_ERR(realfile_out))
                goto out_unlock;

        realfile_in = ovl_real_file(file_in);
        ret = PTR_ERR(realfile_in);
        if (IS_ERR(realfile_in))
                goto out_unlock;

        with_ovl_creds(file_inode(file_out)->i_sb) {
                switch (op) {
                case OVL_COPY:
                        ret = vfs_copy_file_range(realfile_in, pos_in,
                                                  realfile_out, pos_out, len, flags);
                        break;

                case OVL_CLONE:
                        ret = vfs_clone_file_range(realfile_in, pos_in,
                                                   realfile_out, pos_out, len, flags);
                        break;

                case OVL_DEDUPE:
                        ret = vfs_dedupe_file_range_one(realfile_in, pos_in,
                                                        realfile_out, pos_out, len,
                                                        flags);
                        break;
                }
        }

        /* Update size */
        ovl_file_modified(file_out);

out_unlock:
        inode_unlock(inode_out);

        return ret;
}

static ssize_t ovl_copy_file_range(struct file *file_in, loff_t pos_in,
                                   struct file *file_out, loff_t pos_out,
                                   size_t len, unsigned int flags)
{
        return ovl_copyfile(file_in, pos_in, file_out, pos_out, len, flags,
                            OVL_COPY);
}

static loff_t ovl_remap_file_range(struct file *file_in, loff_t pos_in,
                                   struct file *file_out, loff_t pos_out,
                                   loff_t len, unsigned int remap_flags)
{
        enum ovl_copyop op;

        if (remap_flags & ~(REMAP_FILE_DEDUP | REMAP_FILE_ADVISORY))
                return -EINVAL;

        if (remap_flags & REMAP_FILE_DEDUP)
                op = OVL_DEDUPE;
        else
                op = OVL_CLONE;

        /*
         * Don't copy up because of a dedupe request, this wouldn't make sense
         * most of the time (data would be duplicated instead of deduplicated).
         */
        if (op == OVL_DEDUPE &&
            (!ovl_inode_upper(file_inode(file_in)) ||
             !ovl_inode_upper(file_inode(file_out))))
                return -EPERM;

        return ovl_copyfile(file_in, pos_in, file_out, pos_out, len,
                            remap_flags, op);
}

static int ovl_flush(struct file *file, fl_owner_t id)
{
        struct file *realfile;
        int err = 0;

        realfile = ovl_real_file(file);
        if (IS_ERR(realfile))
                return PTR_ERR(realfile);

        if (realfile->f_op->flush) {
                with_ovl_creds(file_inode(file)->i_sb)
                        err = realfile->f_op->flush(realfile, id);
        }

        return err;
}

const struct file_operations ovl_file_operations = {
        .open           = ovl_open,
        .release        = ovl_release,
        .llseek         = ovl_llseek,
        .read_iter      = ovl_read_iter,
        .write_iter     = ovl_write_iter,
        .fsync          = ovl_fsync,
        .mmap           = ovl_mmap,
        .fallocate      = ovl_fallocate,
        .fadvise        = ovl_fadvise,
        .flush          = ovl_flush,
        .splice_read    = ovl_splice_read,
        .splice_write   = ovl_splice_write,

        .copy_file_range        = ovl_copy_file_range,
        .remap_file_range       = ovl_remap_file_range,
        .setlease               = generic_setlease,
};