On Mon, Feb 6, 2017 at 3:24 PM, Takashi Iwai tiwai@suse.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/...

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@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... Reported-by: Dmitry Vyukov dvyukov@google.com Cc: stable@vger.kernel.org Signed-off-by: Takashi Iwai tiwai@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