2022-04-27 17:48:48

by Minchan Kim

Subject: [PATCH] kernfs: fix NULL dereferencing in kernfs_remove

kernfs_remove supported NULL kernfs_node param to bail out but revent
per-fs lock change introduced regression that dereferencing the
param without NULL check so kernel goes crash.

This patch checks the NULL kernfs_node in kernfs_remove and if so,
just return.

Quote from bug report by Jirka

```
The bug is triggered by running NAS Parallel benchmark suite on
SuperMicro servers with 2x Xeon(R) Gold 6126 CPU. Here is the error
log:

[ 247.035564] BUG: kernel NULL pointer dereference, address: 0000000000000008
[ 247.036009] #PF: supervisor read access in kernel mode
[ 247.036009] #PF: error_code(0x0000) - not-present page
[ 247.036009] PGD 0 P4D 0
[ 247.036009] Oops: 0000 [#1] PREEMPT SMP PTI
[ 247.058060] CPU: 1 PID: 6546 Comm: umount Not tainted
5.16.0393c3714081a53795bbff0e985d24146def6f57f+ #16
[ 247.058060] Hardware name: Supermicro Super Server/X11DDW-L, BIOS
2.0b 03/07/2018
[ 247.058060] RIP: 0010:kernfs_remove+0x8/0x50
[ 247.058060] Code: 4c 89 e0 5b 5d 41 5c 41 5d 41 5e c3 49 c7 c4 f4
ff ff ff eb b2 66 66 2e 0f 1f 84 00 00 00 00 00 66 90 0f 1f 44 00 00
41 54 55 <48> 8b 47 08 48 89 fd 48 85 c0 48 0f 44 c7 4c 8b 60 50 49 83
c4 60
[ 247.058060] RSP: 0018:ffffbbfa48a27e48 EFLAGS: 00010246
[ 247.058060] RAX: 0000000000000001 RBX: ffffffff89e31f98 RCX: 0000000080200018
[ 247.058060] RDX: 0000000080200019 RSI: fffff6760786c900 RDI: 0000000000000000
[ 247.058060] RBP: ffffffff89e31f98 R08: ffff926b61b24d00 R09: 0000000080200018
[ 247.122048] R10: ffff926b61b24d00 R11: ffff926a8040c000 R12: ffff927bd09a2000
[ 247.122048] R13: ffffffff89e31fa0 R14: dead000000000122 R15: dead000000000100
[ 247.122048] FS: 00007f01be0a8c40(0000) GS:ffff926fa8e40000(0000)
knlGS:0000000000000000
[ 247.122048] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 247.122048] CR2: 0000000000000008 CR3: 00000001145c6003 CR4: 00000000007706e0
[ 247.122048] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 247.122048] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 247.122048] PKRU: 55555554
[ 247.122048] Call Trace:
[ 247.122048] <TASK>
[ 247.122048] rdt_kill_sb+0x29d/0x350
[ 247.122048] deactivate_locked_super+0x36/0xa0
[ 247.122048] cleanup_mnt+0x131/0x190
[ 247.122048] task_work_run+0x5c/0x90
[ 247.122048] exit_to_user_mode_prepare+0x229/0x230
[ 247.122048] syscall_exit_to_user_mode+0x18/0x40
[ 247.122048] do_syscall_64+0x48/0x90
[ 247.122048] entry_SYSCALL_64_after_hwframe+0x44/0xae
[ 247.122048] RIP: 0033:0x7f01be2d735b
```

Cc: [email protected]
Link: https://bugzilla.kernel.org/show_bug.cgi?id=215696
Link: https://lore.kernel.org/lkml/CAE4VaGDZr_4wzRn2___eDYRtmdPaGGJdzu_LCSkJYuY9BEO3cw@mail.gmail.com/
Fixes: 393c3714081a (kernfs: switch global kernfs_rwsem lock to per-fs lock)
Reported-by: Jirka Hladky <[email protected]>
Tested-by: Jirka Hladky <[email protected]>
Signed-off-by: Minchan Kim <[email protected]>
---
fs/kernfs/dir.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c
index 61a8edc4ba8b..e205fde7163a 100644
--- a/fs/kernfs/dir.c
+++ b/fs/kernfs/dir.c
@@ -1406,7 +1406,12 @@ static void __kernfs_remove(struct kernfs_node *kn)
*/
void kernfs_remove(struct kernfs_node *kn)
{
- struct kernfs_root *root = kernfs_root(kn);
+ struct kernfs_root *root;
+
+ if (!kn)
+ return;
+
+ root = kernfs_root(kn);

down_write(&root->kernfs_rwsem);
__kernfs_remove(kn);
--
2.36.0.rc2.479.g8af0fa9b8e-goog

2022-04-27 17:53:49

by Tejun Heo

Subject: Re: [PATCH] kernfs: fix NULL dereferencing in kernfs_remove

On Wed, Apr 27, 2022 at 10:21:51AM -0700, Minchan Kim wrote:
> kernfs_remove supported NULL kernfs_node param to bail out but revent
^
typo
> per-fs lock change introduced regression that dereferencing the
> param without NULL check so kernel goes crash.
>
> This patch checks the NULL kernfs_node in kernfs_remove and if so,
> just return.
...
> Cc: [email protected]
> Link: https://bugzilla.kernel.org/show_bug.cgi?id=215696
> Link: https://lore.kernel.org/lkml/CAE4VaGDZr_4wzRn2___eDYRtmdPaGGJdzu_LCSkJYuY9BEO3cw@mail.gmail.com/
> Fixes: 393c3714081a (kernfs: switch global kernfs_rwsem lock to per-fs lock)
> Reported-by: Jirka Hladky <[email protected]>
> Tested-by: Jirka Hladky <[email protected]>
> Signed-off-by: Minchan Kim <[email protected]>

Acked-by: Tejun Heo <[email protected]>

Thanks.

--
tejun