Date:   Mon, 6 Feb 2017 16:43:22 +0100
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Takashi Iwai <tiwai@...e.de>
Cc:     alsa-devel@...a-project.org, Jaroslav Kysela <perex@...ex.cz>,
        LKML <linux-kernel@...r.kernel.org>,
        syzkaller <syzkaller@...glegroups.com>
Subject: Re: sound: unable to handle kernel paging request snd_seq_prioq_cell_out

On Mon, Feb 6, 2017 at 3:24 PM, Takashi Iwai <tiwai@...e.de> wrote:
> 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.

Yes, there are such messages.
Applied locally for testing. Thanks!

> Below is a simple fix.  I'm going to queue it to for-linus branch.
>
>
> thanks,
>
> Takashi
>
> -- 8< --
> From: Takashi Iwai <tiwai@...e.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@...gle.com>
> Cc: <stable@...r.kernel.org>
> Signed-off-by: Takashi Iwai <tiwai@...e.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
>

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