[alsa-devel] sound: unable to handle kernel paging request snd_seq_prioq_cell_out

[Takashi Iwai]

On Tue, 31 Jan 2017 11:04:46 +0100,
Dmitry Vyukov wrote:
> 
> Hello,
> 
> The following program triggers wild memory access in snd_seq_prioq_cell_out:
> https://gist.githubusercontent.com/dvyukov/e0bfb47caf577217b3b0550866cba00b/raw/111473e99109fc96a1d3e252c3b8f982e8eaa265/gistfile1.txt
> 
> BUG: unable to handle kernel paging request at ffffc9000392ddb8
> IP: snd_seq_prioq_cell_out+0x11d/0x260 sound/core/seq/seq_prioq.c:231
> PGD 6cc6f067
> PUD 6cc70067
> PMD 5f94c067
> PTE 0
> Oops: 0000 [#1] SMP KASAN
> Modules linked in:
> CPU: 2 PID: 375 Comm: syz-executor Not tainted 4.10.0-rc5+ #201
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
> task: ffff880066f92500 task.stack: ffff88005f740000
> RIP: 0010:snd_seq_prioq_cell_out+0x11d/0x260 sound/core/seq/seq_prioq.c:231
> RSP: 0018:ffff88005f7470b8 EFLAGS: 00010046
> RAX: dffffc0000000000 RBX: 1ffff1000bee8e18 RCX: ffffc90000c22000
> RDX: 1ffff92000725bb7 RSI: ffffffff8348787e RDI: ffffc9000392ddb8
> RBP: ffff88005f747208 R08: 0000000000000001 R09: 0000000000000001
> R10: dffffc0000000000 R11: 0000000000000004 R12: ffff8800673cbe80
> R13: ffff88005f7471e0 R14: ffffc9000392dd90 R15: ffff8800673cbe98
> FS:  00007f5262fee700(0000) GS:ffff88006d100000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: ffffc9000392ddb8 CR3: 0000000066209000 CR4: 00000000001406e0
> Call Trace:
>  snd_seq_prioq_delete+0x8b/0xf0 sound/core/seq/seq_prioq.c:90
>  queue_delete+0x77/0xb0 sound/core/seq/seq_queue.c:152
>  snd_seq_queue_client_leave+0x34/0x130 sound/core/seq/seq_queue.c:595
>  seq_free_client1.part.5+0x10a/0x410 sound/core/seq/seq_clientmgr.c:258
>  seq_free_client1 sound/core/seq/seq_clientmgr.c:255 [inline]
>  seq_free_client+0x6f/0x170 sound/core/seq/seq_clientmgr.c:284
>  snd_seq_release+0x51/0xe0 sound/core/seq/seq_clientmgr.c:366
>  __fput+0x332/0x7f0 fs/file_table.c:208
>  ____fput+0x15/0x20 fs/file_table.c:244
>  task_work_run+0x18a/0x260 kernel/task_work.c:116
>  get_signal+0x148f/0x1820 kernel/signal.c:2143
>  do_signal+0xd2/0x2190 arch/x86/kernel/signal.c:807
>  exit_to_usermode_loop+0x200/0x2a0 arch/x86/entry/common.c:156
>  prepare_exit_to_usermode arch/x86/entry/common.c:190 [inline]
>  syscall_return_slowpath+0x4d3/0x570 arch/x86/entry/common.c:259
>  entry_SYSCALL_64_fastpath+0xc0/0xc2
> RIP: 0033:0x4457d9
> RSP: 002b:00007f5262fedb58 EFLAGS: 00000286 ORIG_RAX: 0000000000000010
> RAX: 0000000000000000 RBX: 00000000007080a8 RCX: 00000000004457d9
> RDX: 0000000020001000 RSI: 000000004058534c RDI: 0000000000000005
> RBP: 0000000000002250 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000286 R12: 00000000006e0310
> R13: 0000000000000005 R14: 000000004058534c R15: 0000000020001000
> Code: f6 0f 84 90 00 00 00 e8 02 1e 2a fe 49 8d 7e 28 48 b8 00 00 00
> 00 00 fc ff df 48 89 fa 48 c1 ea 03 80 3c 02 00 0f 85 1f 01 00 00 <49>
> 8b 46 28 49 8d 7c 24 08 48 89 fa 49 89 04 24 48 c1 ea 03 48
> RIP: snd_seq_prioq_cell_out+0x11d/0x260 sound/core/seq/seq_prioq.c:231
> RSP: ffff88005f7470b8
> CR2: ffffc9000392ddb8
> ---[ end trace cbaec69c4a9fdbfc ]---
> 
> On commit fd694aaa46c7ed811b72eb47d5eb11ce7ab3f7f1 (Jan 26).

This is due to a forced resource release after the loop timeout.
You must have seen a message like
  ALSA: snd_seq_pool_done timeout: 1 cells remain
before the Oops.

Below is a simple fix.  I'm going to queue it to for-linus branch.


thanks,

Takashi

-- 8< --
From: Takashi Iwai <tiwai at suse.de>
Subject: [PATCH] ALSA: seq: Don't handle loop timeout at snd_seq_pool_done()

snd_seq_pool_done() syncs with closing of all opened threads, but it
aborts the wait loop with a timeout, and proceeds to the release
resource even if not all threads have been closed.  The timeout was 5
seconds, and if you run a crazy stuff, it can exceed easily, and may
result in the access of the invalid memory address -- this is what
syzkaller detected in a bug report.

As a fix, let the code graduate from naiveness, simply remove the loop
timeout.

BugLink: http://lkml.kernel.org/r/CACT4Y+YdhDV2H5LLzDTJDVF-qiYHUHhtRaW4rbb4gUhTCQB81w@mail.gmail.com
Reported-by: Dmitry Vyukov <dvyukov at google.com>
Cc: <stable at vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai at suse.de>
---
 sound/core/seq/seq_memory.c | 9 +--------
 1 file changed, 1 insertion(+), 8 deletions(-)

diff --git a/sound/core/seq/seq_memory.c b/sound/core/seq/seq_memory.c
index c850345c43b5..dfa5156f3585 100644
--- a/sound/core/seq/seq_memory.c
+++ b/sound/core/seq/seq_memory.c
@@ -419,7 +419,6 @@ int snd_seq_pool_done(struct snd_seq_pool *pool)
 {
 	unsigned long flags;
 	struct snd_seq_event_cell *ptr;
-	int max_count = 5 * HZ;
 
 	if (snd_BUG_ON(!pool))
 		return -EINVAL;
@@ -432,14 +431,8 @@ int snd_seq_pool_done(struct snd_seq_pool *pool)
 	if (waitqueue_active(&pool->output_sleep))
 		wake_up(&pool->output_sleep);
 
-	while (atomic_read(&pool->counter) > 0) {
-		if (max_count == 0) {
-			pr_warn("ALSA: snd_seq_pool_done timeout: %d cells remain\n", atomic_read(&pool->counter));
-			break;
-		}
+	while (atomic_read(&pool->counter) > 0)
 		schedule_timeout_uninterruptible(1);
-		max_count--;
-	}
 	
 	/* release all resources */
 	spin_lock_irqsave(&pool->lock, flags);
-- 
2.11.0