[SRU][J][PATCH 0/1] cifs: NULL pointer dereference in refresh_cache_worker

[Chengen Du]

BugLink: https://bugs.launchpad.net/bugs/2112440

SRU Justification:

[Impact]
When refresh_cache_worker attempts to refresh DFS referrals, it may access uninitialized data, leading to a general protection fault caused by a NULL pointer dereference.

[Fix]
There is an upstream commit that addresses this issue:

>From 41f10081a92a0ed280008218a8ec18ad8ba0fceb Mon Sep 17 00:00:00 2001
From: Paulo Alcantara <pc at cjr.nz>
Date: Wed, 20 Apr 2022 21:05:45 -0300
Subject: [PATCH] cifs: fix NULL ptr dereference in refresh_mounts()

Either mount(2) or automount might not have server->origin_fullpath
set yet while refresh_cache_worker() is attempting to refresh DFS
referrals. Add missing NULL check and locking around it.

This fixes bellow crash:

[ 1070.276835] general protection fault, probably for non-canonical address 0xdffffc0000000000: 0000 [#1] PREEMPT SMP KASAN NOPTI
[ 1070.277676] KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007]
[ 1070.278219] CPU: 1 PID: 8506 Comm: kworker/u8:1 Not tainted 5.18.0-rc3 #10
[ 1070.278701] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.15.0-0-g2dd4b9b-rebuilt.opensuse.org 04/01/2014
[ 1070.279495] Workqueue: cifs-dfscache refresh_cache_worker [cifs]
[ 1070.280044] RIP: 0010:strcasecmp+0x34/0x150
[ 1070.280359] Code: 00 00 00 fc ff df 41 54 55 48 89 fd 53 48 83 ec 10 eb 03 4c 89 fe 48 89 ef 48 83 c5 01 48 89 f8 48 89 fa 48 c1 e8 03 83 e2 07 <42> 0f b6 04 28 38 d0 7f 08 84 c0 0f 85 bc 00 00 00 0f b6 45 ff 44
[ 1070.281729] RSP: 0018:ffffc90008367958 EFLAGS: 00010246
[ 1070.282114] RAX: 0000000000000000 RBX: dffffc0000000000 RCX: 0000000000000000
[ 1070.282691] RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
[ 1070.283273] RBP: 0000000000000001 R08: 0000000000000000 R09: ffffffff873eda27
[ 1070.283857] R10: ffffc900083679a0 R11: 0000000000000001 R12: ffff88812624c000
[ 1070.284436] R13: dffffc0000000000 R14: ffff88810e6e9a88 R15: ffff888119bb9000
[ 1070.284990] FS: 0000000000000000(0000) GS:ffff888151200000(0000) knlGS:0000000000000000
[ 1070.285625] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 1070.286100] CR2: 0000561a4d922418 CR3: 000000010aecc000 CR4: 0000000000350ee0
[ 1070.286683] Call Trace:
[ 1070.286890] <TASK>
[ 1070.287070] refresh_cache_worker+0x895/0xd20 [cifs]
[ 1070.287475] ? __refresh_tcon.isra.0+0xfb0/0xfb0 [cifs]
[ 1070.287905] ? __lock_acquire+0xcd1/0x6960
[ 1070.288247] ? is_dynamic_key+0x1a0/0x1a0
[ 1070.288591] ? lockdep_hardirqs_on_prepare+0x410/0x410
[ 1070.289012] ? lock_downgrade+0x6f0/0x6f0
[ 1070.289318] process_one_work+0x7bd/0x12d0
[ 1070.289637] ? worker_thread+0x160/0xec0
[ 1070.289970] ? pwq_dec_nr_in_flight+0x230/0x230
[ 1070.290318] ? _raw_spin_lock_irq+0x5e/0x90
[ 1070.290619] worker_thread+0x5ac/0xec0
[ 1070.290891] ? process_one_work+0x12d0/0x12d0
[ 1070.291199] kthread+0x2a5/0x350
[ 1070.291430] ? kthread_complete_and_exit+0x20/0x20
[ 1070.291770] ret_from_fork+0x22/0x30
[ 1070.292050] </TASK>
[ 1070.292223] Modules linked in: bpfilter cifs cifs_arc4 cifs_md4
[ 1070.292765] ---[ end trace 0000000000000000 ]---
[ 1070.293108] RIP: 0010:strcasecmp+0x34/0x150
[ 1070.293471] Code: 00 00 00 fc ff df 41 54 55 48 89 fd 53 48 83 ec 10 eb 03 4c 89 fe 48 89 ef 48 83 c5 01 48 89 f8 48 89 fa 48 c1 e8 03 83 e2 07 <42> 0f b6 04 28 38 d0 7f 08 84 c0 0f 85 bc 00 00 00 0f b6 45 ff 44
[ 1070.297718] RSP: 0018:ffffc90008367958 EFLAGS: 00010246
[ 1070.298622] RAX: 0000000000000000 RBX: dffffc0000000000 RCX: 0000000000000000
[ 1070.299428] RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
[ 1070.300296] RBP: 0000000000000001 R08: 0000000000000000 R09: ffffffff873eda27
[ 1070.301204] R10: ffffc900083679a0 R11: 0000000000000001 R12: ffff88812624c000
[ 1070.301932] R13: dffffc0000000000 R14: ffff88810e6e9a88 R15: ffff888119bb9000
[ 1070.302645] FS: 0000000000000000(0000) GS:ffff888151200000(0000) knlGS:0000000000000000
[ 1070.303462] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 1070.304131] CR2: 0000561a4d922418 CR3: 000000010aecc000 CR4: 0000000000350ee0
[ 1070.305004] Kernel panic - not syncing: Fatal exception
[ 1070.305711] Kernel Offset: disabled
[ 1070.305971] ---[ end Kernel panic - not syncing: Fatal exception ]---

[Test Plan]
This is a timing issue that is difficult to reproduce reliably.
The fix involves adding proper locking and NULL checks.
Since reproducing the problem is challenging, we can instead focus on verifying that the normal behavior remains correct.
1. Prepare a Windows environment with DFS configured.
2. Mount the Windows DFS share using CIFS and confirm it is accessible.
mount -t cifs -v //dfs-server/share /mnt/ -o username=XXX,vers=3.0
3. Remount the share and verify that it remains accessible.
mount -t cifs -v //dfs-server/share /mnt/ -o remount,rw,username=XXX,vers=3.0

[Where problems could occur]
The fix introduces locking and NULL checks in the CIFS code.
If any regressions occur, they could significantly impact CIFS functionality.

Paulo Alcantara (1):
  cifs: fix NULL ptr dereference in refresh_mounts()

 fs/cifs/connect.c   |  2 ++
 fs/cifs/dfs_cache.c | 19 ++++++++++++-------
 2 files changed, 14 insertions(+), 7 deletions(-)

-- 
2.43.0