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

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Date:   Mon, 27 Jun 2022 13:21:15 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Marc Dionne <marc.dionne@...istor.com>,
        David Howells <dhowells@...hat.com>,
        linux-afs@...ts.infradead.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.15 068/135] afs: Fix dynamic root getattr

From: David Howells <dhowells@...hat.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@...istor.com>
Signed-off-by: David Howells <dhowells@...hat.com>
Reviewed-by: Marc Dionne <marc.dionne@...istor.com>
Tested-by: Marc Dionne <marc.dionne@...istor.com>
cc: linux-afs@...ts.infradead.org
Link: https://lore.kernel.org/r/165408450783.1031787.7941404776393751186.stgit@warthog.procyon.org.uk/
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Sasha Levin <sashal@...nel.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