[PATCH 5.15 45/84] afs: Fix endless loop in directory parsing

Greg Kroah-Hartman
2024-03-04T21:55:16Z

From: David Howells <dhowells@redhat.com>

[ Upstream commit 5f7a07646655fb4108da527565dcdc80124b14c4 ]

If a directory has a block with only ".__afsXXXX" files in it (from
uncompleted silly-rename), these .__afsXXXX files are skipped but without
advancing the file position in the dir_context. This leads to
afs_dir_iterate() repeating the block again and again.

Fix this by making the code that skips the .__afsXXXX file also manually
advance the file position.

The symptoms are a soft lookup:

watchdog: BUG: soft lockup - CPU#3 stuck for 52s! [check:5737]
...
RIP: 0010:afs_dir_iterate_block+0x39/0x1fd
...
? watchdog_timer_fn+0x1a6/0x213
...
? asm_sysvec_apic_timer_interrupt+0x16/0x20
? afs_dir_iterate_block+0x39/0x1fd
afs_dir_iterate+0x10a/0x148
afs_readdir+0x30/0x4a
iterate_dir+0x93/0xd3
__do_sys_getdents64+0x6b/0xd4

This is almost certainly the actual fix for:

https://bugzilla.kernel.org/show_bug.cgi?id=218496

Fixes: 57e9d49c5452 ("afs: Hide silly-rename files from userspace")
Signed-off-by: David Howells <dhowells@redhat.com>
Link: https://lore.kernel.org/r/786185.1708694102@warthog.procyon.org.uk
Reviewed-by: Marc Dionne <marc.dionne@auristor.com>
cc: Marc Dionne <marc.dionne@auristor.com>
cc: Markus Suvanto <markus.suvanto@gmail.com>
cc: linux-afs@lists.infradead.org
Signed-off-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
fs/afs/dir.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/fs/afs/dir.c b/fs/afs/dir.c
index 106426de50279..c4e22e9f7a666 100644
--- a/fs/afs/dir.c
+++ b/fs/afs/dir.c
@@ -497,8 +497,10 @@ static int afs_dir_iterate_block(struct afs_vnode *dvnode,
dire->u.name[0] == '.' &&
ctx->actor != afs_lookup_filldir &&
ctx->actor != afs_lookup_one_filldir &&
- memcmp(dire->u.name, ".__afs", 6) == 0)
+ memcmp(dire->u.name, ".__afs", 6) == 0) {
+ ctx->pos = blkoff + next * sizeof(union afs_xdr_dirent);
continue;
+ }

/* found the next entry */
if (!dir_emit(ctx, dire->u.name, nlen,
--
2.43.0