// SPDX-License-Identifier: GPL-2.0-only

#include <linux/fs.h>
#include <linux/xattr.h>
#include "overlayfs.h"

static bool ovl_is_escaped_xattr(struct super_block *sb, const char *name)
{
        struct ovl_fs *ofs = sb->s_fs_info;

        if (ofs->config.userxattr)
                return strncmp(name, OVL_XATTR_ESCAPE_USER_PREFIX,
                               OVL_XATTR_ESCAPE_USER_PREFIX_LEN) == 0;
        else
                return strncmp(name, OVL_XATTR_ESCAPE_TRUSTED_PREFIX,
                               OVL_XATTR_ESCAPE_TRUSTED_PREFIX_LEN - 1) == 0;
}

static bool ovl_is_own_xattr(struct super_block *sb, const char *name)
{
        struct ovl_fs *ofs = OVL_FS(sb);

        if (ofs->config.userxattr)
                return strncmp(name, OVL_XATTR_USER_PREFIX,
                               OVL_XATTR_USER_PREFIX_LEN) == 0;
        else
                return strncmp(name, OVL_XATTR_TRUSTED_PREFIX,
                               OVL_XATTR_TRUSTED_PREFIX_LEN) == 0;
}

bool ovl_is_private_xattr(struct super_block *sb, const char *name)
{
        return ovl_is_own_xattr(sb, name) && !ovl_is_escaped_xattr(sb, name);
}

static int ovl_xattr_set(struct dentry *dentry, struct inode *inode, const char *name,
                         const void *value, size_t size, int flags)
{
        int err;
        struct ovl_fs *ofs = OVL_FS(dentry->d_sb);
        struct dentry *upperdentry = ovl_i_dentry_upper(inode);
        struct dentry *realdentry = upperdentry ?: ovl_dentry_lower(dentry);
        struct path realpath;

        if (!value && !upperdentry) {
                ovl_path_lower(dentry, &realpath);
                with_ovl_creds(dentry->d_sb)
                        err = vfs_getxattr(mnt_idmap(realpath.mnt), realdentry, name, NULL, 0);
                if (err < 0)
                        goto out;
        }

        if (!upperdentry) {
                err = ovl_copy_up(dentry);
                if (err)
                        goto out;

                realdentry = ovl_dentry_upper(dentry);
        }

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

        with_ovl_creds(dentry->d_sb) {
                if (value) {
                        err = ovl_do_setxattr(ofs, realdentry, name, value, size, flags);
                } else {
                        WARN_ON(flags != XATTR_REPLACE);
                        err = ovl_do_removexattr(ofs, realdentry, name);
                }
        }
        ovl_drop_write(dentry);

        /* copy c/mtime */
        ovl_copyattr(inode);
out:
        return err;
}

static int ovl_xattr_get(struct dentry *dentry, struct inode *inode, const char *name,
                         void *value, size_t size)
{
        struct path realpath;

        ovl_i_path_real(inode, &realpath);
        with_ovl_creds(dentry->d_sb)
                return vfs_getxattr(mnt_idmap(realpath.mnt), realpath.dentry, name, value, size);
}

static bool ovl_can_list(struct super_block *sb, const char *s)
{
        /* Never list private (.overlay) */
        if (ovl_is_private_xattr(sb, s))
                return false;

        /* List all non-trusted xattrs */
        if (strncmp(s, XATTR_TRUSTED_PREFIX, XATTR_TRUSTED_PREFIX_LEN) != 0)
                return true;

        /* list other trusted for superuser only */
        return ns_capable_noaudit(&init_user_ns, CAP_SYS_ADMIN);
}

ssize_t ovl_listxattr(struct dentry *dentry, char *list, size_t size)
{
        struct dentry *realdentry = ovl_dentry_real(dentry);
        struct ovl_fs *ofs = OVL_FS(dentry->d_sb);
        ssize_t res;
        size_t len;
        char *s;
        size_t prefix_len, name_len;

        with_ovl_creds(dentry->d_sb)
                res = vfs_listxattr(realdentry, list, size);
        if (res <= 0 || size == 0)
                return res;

        prefix_len = ofs->config.userxattr ?
                OVL_XATTR_USER_PREFIX_LEN : OVL_XATTR_TRUSTED_PREFIX_LEN;

        /* filter out private xattrs */
        for (s = list, len = res; len;) {
                size_t slen = strnlen(s, len) + 1;

                /* underlying fs providing us with an broken xattr list? */
                if (WARN_ON(slen > len))
                        return -EIO;

                len -= slen;
                if (!ovl_can_list(dentry->d_sb, s)) {
                        res -= slen;
                        memmove(s, s + slen, len);
                } else if (ovl_is_escaped_xattr(dentry->d_sb, s)) {
                        res -= OVL_XATTR_ESCAPE_PREFIX_LEN;
                        name_len = slen - prefix_len - OVL_XATTR_ESCAPE_PREFIX_LEN;
                        s += prefix_len;
                        memmove(s, s + OVL_XATTR_ESCAPE_PREFIX_LEN, name_len + len);
                        s += name_len;
                } else {
                        s += slen;
                }
        }

        return res;
}

static char *ovl_xattr_escape_name(const char *prefix, const char *name)
{
        size_t prefix_len = strlen(prefix);
        size_t name_len = strlen(name);
        size_t escaped_len;
        char *escaped, *s;

        escaped_len = prefix_len + OVL_XATTR_ESCAPE_PREFIX_LEN + name_len;
        if (escaped_len > XATTR_NAME_MAX)
                return ERR_PTR(-EOPNOTSUPP);

        escaped = kmalloc(escaped_len + 1, GFP_KERNEL);
        if (escaped == NULL)
                return ERR_PTR(-ENOMEM);

        s = escaped;
        memcpy(s, prefix, prefix_len);
        s += prefix_len;
        memcpy(s, OVL_XATTR_ESCAPE_PREFIX, OVL_XATTR_ESCAPE_PREFIX_LEN);
        s += OVL_XATTR_ESCAPE_PREFIX_LEN;
        memcpy(s, name, name_len + 1);

        return escaped;
}

static int ovl_own_xattr_get(const struct xattr_handler *handler,
                             struct dentry *dentry, struct inode *inode,
                             const char *name, void *buffer, size_t size)
{
        char *escaped;
        int r;

        escaped = ovl_xattr_escape_name(handler->prefix, name);
        if (IS_ERR(escaped))
                return PTR_ERR(escaped);

        r = ovl_xattr_get(dentry, inode, escaped, buffer, size);

        kfree(escaped);

        return r;
}

static int ovl_own_xattr_set(const struct xattr_handler *handler,
                             struct mnt_idmap *idmap,
                             struct dentry *dentry, struct inode *inode,
                             const char *name, const void *value,
                             size_t size, int flags)
{
        char *escaped;
        int r;

        escaped = ovl_xattr_escape_name(handler->prefix, name);
        if (IS_ERR(escaped))
                return PTR_ERR(escaped);

        r = ovl_xattr_set(dentry, inode, escaped, value, size, flags);

        kfree(escaped);

        return r;
}

static int ovl_other_xattr_get(const struct xattr_handler *handler,
                               struct dentry *dentry, struct inode *inode,
                               const char *name, void *buffer, size_t size)
{
        return ovl_xattr_get(dentry, inode, name, buffer, size);
}

static int ovl_other_xattr_set(const struct xattr_handler *handler,
                               struct mnt_idmap *idmap,
                               struct dentry *dentry, struct inode *inode,
                               const char *name, const void *value,
                               size_t size, int flags)
{
        return ovl_xattr_set(dentry, inode, name, value, size, flags);
}

static const struct xattr_handler ovl_own_trusted_xattr_handler = {
        .prefix = OVL_XATTR_TRUSTED_PREFIX,
        .get = ovl_own_xattr_get,
        .set = ovl_own_xattr_set,
};

static const struct xattr_handler ovl_own_user_xattr_handler = {
        .prefix = OVL_XATTR_USER_PREFIX,
        .get = ovl_own_xattr_get,
        .set = ovl_own_xattr_set,
};

static const struct xattr_handler ovl_other_xattr_handler = {
        .prefix = "", /* catch all */
        .get = ovl_other_xattr_get,
        .set = ovl_other_xattr_set,
};

static const struct xattr_handler * const ovl_trusted_xattr_handlers[] = {
        &ovl_own_trusted_xattr_handler,
        &ovl_other_xattr_handler,
        NULL
};

static const struct xattr_handler * const ovl_user_xattr_handlers[] = {
        &ovl_own_user_xattr_handler,
        &ovl_other_xattr_handler,
        NULL
};

const struct xattr_handler * const *ovl_xattr_handlers(struct ovl_fs *ofs)
{
        return ofs->config.userxattr ? ovl_user_xattr_handlers :
                ovl_trusted_xattr_handlers;
}