[PATCH 5.15 068/135] afs: Fix dynamic root getattr

Greg Kroah-Hartman
2022-06-27T11:40:22Z

From: David Howells <dhowells@redhat.com>

[ Upstream commit cb78d1b5efffe4cf97e16766329dd7358aed3deb ]

The recent patch to make afs_getattr consult the server didn't account
for the pseudo-inodes employed by the dynamic root-type afs superblock
not having a volume or a server to access, and thus an oops occurs if
such a directory is stat'd.

Fix this by checking to see if the vnode->volume pointer actually points
anywhere before following it in afs_getattr().

This can be tested by stat'ing a directory in /afs. It may be
sufficient just to do "ls /afs" and the oops looks something like:

BUG: kernel NULL pointer dereference, address: 0000000000000020
...
RIP: 0010:afs_getattr+0x8b/0x14b
...
Call Trace:
<TASK>
vfs_statx+0x79/0xf5
vfs_fstatat+0x49/0x62

Fixes: 2aeb8c86d499 ("afs: Fix afs_getattr() to refetch file status if callback break occurred")
Reported-by: Marc Dionne <marc.dionne@auristor.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Marc Dionne <marc.dionne@auristor.com>
Tested-by: Marc Dionne <marc.dionne@auristor.com>
cc: linux-afs@lists.infradead.org
Link: https://lore.kernel.org/r/165408450783.1031787.7941404776393751186.stgit@warthog.procyon.org.uk/
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
fs/afs/inode.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/afs/inode.c b/fs/afs/inode.c
index a47666ba48f5..785bacb972da 100644
--- a/fs/afs/inode.c
+++ b/fs/afs/inode.c
@@ -733,7 +733,8 @@ int afs_getattr(struct user_namespace *mnt_userns, const struct path *path,

_enter("{ ino=%lu v=%u }", inode->i_ino, inode->i_generation);

- if (!(query_flags & AT_STATX_DONT_SYNC) &&
+ if (vnode->volume &&
+ !(query_flags & AT_STATX_DONT_SYNC) &&
!test_bit(AFS_VNODE_CB_PROMISED, &vnode->flags)) {
key = afs_request_key(vnode->volume->cell);
if (IS_ERR(key))
--
2.35.1