From: Dominique Martinet asmadeus@codewreck.org

commit c898afdc15645efb555acb6d85b484eb40a45409 upstream.

Fix a use-after-free on dentry's d_fsdata fid list when a thread looks up a fid through dentry while another thread unlinks it:

UAF thread: refcount_t: addition on 0; use-after-free. p9_fid_get linux/./include/net/9p/client.h:262 v9fs_fid_find+0x236/0x280 linux/fs/9p/fid.c:129 v9fs_fid_lookup_with_uid linux/fs/9p/fid.c:181 v9fs_fid_lookup+0xbf/0xc20 linux/fs/9p/fid.c:314 v9fs_vfs_getattr_dotl+0xf9/0x360 linux/fs/9p/vfs_inode_dotl.c:400 vfs_statx+0xdd/0x4d0 linux/fs/stat.c:248

Freed by: p9_fid_destroy (inlined) p9_client_clunk+0xb0/0xe0 linux/net/9p/client.c:1456 p9_fid_put linux/./include/net/9p/client.h:278 v9fs_dentry_release+0xb5/0x140 linux/fs/9p/vfs_dentry.c:55 v9fs_remove+0x38f/0x620 linux/fs/9p/vfs_inode.c:518 vfs_unlink+0x29a/0x810 linux/fs/namei.c:4335

The problem is that d_fsdata was not accessed under d_lock, because d_release() normally is only called once the dentry is otherwise no longer accessible but since we also call it explicitly in v9fs_remove that lock is required: move the hlist out of the dentry under lock then unref its fids once they are no longer accessible.

Fixes: 154372e67d40 ("fs/9p: fix create-unlink-getattr idiom") Cc: stable@vger.kernel.org Reported-by: Meysam Firouzi Reported-by: Amirmohammad Eftekhar Reviewed-by: Christian Schoenebeck linux_oss@crudebyte.com Message-ID: 20240521122947.1080227-1-asmadeus@codewreck.org Signed-off-by: Dominique Martinet asmadeus@codewreck.org [Samasth: backport to 5.15.y] Signed-off-by: Samasth Norway Ananda samasth.norway.ananda@oracle.com

Conflicts: fs/9p/vfs_dentry.c keep p9_client_clunk instead of introducing the helper function p9_fid_get/put from commit b48dbb998d70 ("9p fid refcount: add p9_fid_get/put wrappers") --- This is a fix for CVE-2024-39463, minor conflict resolution involved. --- fs/9p/vfs_dentry.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/fs/9p/vfs_dentry.c b/fs/9p/vfs_dentry.c index c2736af97884f..afcf4711ac2a8 100644 --- a/fs/9p/vfs_dentry.c +++ b/fs/9p/vfs_dentry.c @@ -52,12 +52,17 @@ static int v9fs_cached_dentry_delete(const struct dentry *dentry) static void v9fs_dentry_release(struct dentry *dentry) { struct hlist_node *p, *n; + struct hlist_head head;

p9_debug(P9_DEBUG_VFS, " dentry: %pd (%p)\n", dentry, dentry); - hlist_for_each_safe(p, n, (struct hlist_head *)&dentry->d_fsdata) + + spin_lock(&dentry->d_lock); + hlist_move_list((struct hlist_head *)&dentry->d_fsdata, &head); + spin_unlock(&dentry->d_lock); + + hlist_for_each_safe(p, n, &head) p9_client_clunk(hlist_entry(p, struct p9_fid, dlist)); - dentry->d_fsdata = NULL; }

static int v9fs_lookup_revalidate(struct dentry *dentry, unsigned int flags)