6.10-stable review patch. If anyone has any objections, please let me know.
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From: Christian Brauner brauner@kernel.org
commit 4e32c25b58b945f976435bbe51f39b32d714052e upstream.
get_stashed_dentry() tries to optimistically retrieve a stashed dentry from a provided location. It needs to ensure to hold rcu lock before it dereference the stashed location to prevent UAF issues. Use rcu_dereference() instead of READ_ONCE() it's effectively equivalent with some lockdep bells and whistles and it communicates clearly that this expects rcu protection.
Link: https://lore.kernel.org/r/20240906-vfs-hotfix-5959800ffa68@brauner Fixes: 07fd7c329839 ("libfs: add path_from_stashed()") Reported-by: syzbot+f82b36bffae7ef78b6a7@syzkaller.appspotmail.com Fixes: syzbot+f82b36bffae7ef78b6a7@syzkaller.appspotmail.com Reported-by: syzbot+cbe4b96e1194b0e34db6@syzkaller.appspotmail.com Fixes: syzbot+cbe4b96e1194b0e34db6@syzkaller.appspotmail.com Signed-off-by: Christian Brauner brauner@kernel.org Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- fs/libfs.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-)
--- a/fs/libfs.c +++ b/fs/libfs.c @@ -2043,12 +2043,12 @@ struct timespec64 simple_inode_init_ts(s } EXPORT_SYMBOL(simple_inode_init_ts);
-static inline struct dentry *get_stashed_dentry(struct dentry *stashed) +static inline struct dentry *get_stashed_dentry(struct dentry **stashed) { struct dentry *dentry;
guard(rcu)(); - dentry = READ_ONCE(stashed); + dentry = rcu_dereference(*stashed); if (!dentry) return NULL; if (!lockref_get_not_dead(&dentry->d_lockref)) @@ -2145,7 +2145,7 @@ int path_from_stashed(struct dentry **st const struct stashed_operations *sops = mnt->mnt_sb->s_fs_info;
/* See if dentry can be reused. */ - path->dentry = get_stashed_dentry(*stashed); + path->dentry = get_stashed_dentry(stashed); if (path->dentry) { sops->put_data(data); goto out_path;