Re: [PATCH v2 14/20] fuse_dentry_revalidate(): use stable parent inode and name passed by caller

Jeff Layton
2025-01-17T15:18:34Z

On Thu, 2025-01-16 at 05:23 +0000, Al Viro wrote:
> No need to mess with dget_parent() for the former; for the latter we really should
> not rely upon ->d_name.name remaining stable - it's a real-life UAF.
>
> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
> ---
> fs/fuse/dir.c | 11 +++--------
> 1 file changed, 3 insertions(+), 8 deletions(-)
>
> diff --git a/fs/fuse/dir.c b/fs/fuse/dir.c
> index d9e9f26917eb..7e93a8470c36 100644
> --- a/fs/fuse/dir.c
> +++ b/fs/fuse/dir.c
> @@ -196,7 +196,6 @@ static int fuse_dentry_revalidate(struct inode *dir, const struct qstr *name,
> struct dentry *entry, unsigned int flags)
> {
> struct inode *inode;
> - struct dentry *parent;
> struct fuse_mount *fm;
> struct fuse_inode *fi;
> int ret;
> @@ -228,11 +227,9 @@ static int fuse_dentry_revalidate(struct inode *dir, const struct qstr *name,
>
> attr_version = fuse_get_attr_version(fm->fc);
>
> - parent = dget_parent(entry);
> - fuse_lookup_init(fm->fc, &args, get_node_id(d_inode(parent)),
> - &entry->d_name, &outarg);
> + fuse_lookup_init(fm->fc, &args, get_node_id(dir),
> + name, &outarg);
> ret = fuse_simple_request(fm, &args);
> - dput(parent);
> /* Zero nodeid is same as -ENOENT */
> if (!ret && !outarg.nodeid)
> ret = -ENOENT;
> @@ -266,9 +263,7 @@ static int fuse_dentry_revalidate(struct inode *dir, const struct qstr *name,
> if (test_bit(FUSE_I_INIT_RDPLUS, &fi->state))
> return -ECHILD;
> } else if (test_and_clear_bit(FUSE_I_INIT_RDPLUS, &fi->state)) {
> - parent = dget_parent(entry);
> - fuse_advise_use_readdirplus(d_inode(parent));
> - dput(parent);
> + fuse_advise_use_readdirplus(dir);
> }
> }
> ret = 1;

Reviewed-by: Jeff Layton <jlayton@kernel.org>