Re: sound: WARNING in snd_seq_oss_synth_cleanup

[Takashi Iwai]

On Sun, 24 Jan 2016 11:26:47 +0100,
Dmitry Vyukov wrote:
> 
> Hello,
> 
> The following program triggers WARNING in snd_seq_oss_synth_cleanup:
> 
> ------------[ cut here ]------------
> WARNING: CPU: 1 PID: 7573 at sound/core/seq/oss/seq_oss_synth.c:311
> snd_seq_oss_synth_cleanup+0x35f/0x420()
> Modules linked in:
> CPU: 1 PID: 7573 Comm: a.out Tainted: G        W       4.4.0+ #276
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
>  00000000ffffffff ffff880036bcfbb0 ffffffff82999e2d 0000000000000000
>  ffff8800339797c0 ffffffff86d46580 ffff880036bcfbf0 ffffffff81352089
>  ffffffff84fd380f ffffffff86d46580 0000000000000137 ffff880033e592e8
> Call Trace:
>  [<     inline     >] __dump_stack lib/dump_stack.c:15
>  [<ffffffff82999e2d>] dump_stack+0x6f/0xa2 lib/dump_stack.c:50
>  [<ffffffff81352089>] warn_slowpath_common+0xd9/0x140 kernel/panic.c:482
>  [<ffffffff813522b9>] warn_slowpath_null+0x29/0x30 kernel/panic.c:515
>  [<ffffffff84fd380f>] snd_seq_oss_synth_cleanup+0x35f/0x420
> sound/core/seq/oss/seq_oss_synth.c:311
>  [<ffffffff84fca919>] snd_seq_oss_release+0x79/0x130
> sound/core/seq/oss/seq_oss_init.c:427
>  [<ffffffff84fc8faa>] odev_release+0x5a/0x80 sound/core/seq/oss/seq_oss.c:155
>  [<ffffffff817b73c6>] __fput+0x236/0x780 fs/file_table.c:208
>  [<ffffffff817b7995>] ____fput+0x15/0x20 fs/file_table.c:244
>  [<ffffffff813afdc0>] task_work_run+0x170/0x210 kernel/task_work.c:115
>  [<     inline     >] exit_task_work include/linux/task_work.h:21
>  [<ffffffff8135b275>] do_exit+0x8b5/0x2c60 kernel/exit.c:750
>  [<ffffffff8135d798>] do_group_exit+0x108/0x330 kernel/exit.c:880
>  [<     inline     >] SYSC_exit_group kernel/exit.c:891
>  [<ffffffff8135d9dd>] SyS_exit_group+0x1d/0x20 kernel/exit.c:889
>  [<ffffffff86336c36>] entry_SYSCALL_64_fastpath+0x16/0x7a
> arch/x86/entry/entry_64.S:185
> ---[ end trace e71270304b7f911a ]---
> 
> 
> // autogenerated by syzkaller (http://github.com/google/syzkaller)
> #include <sys/types.h>
> #include <sys/stat.h>
> #include <fcntl.h>
> 
> int main()
> {
>     open("/dev/char/14:8", O_RDWR);
> }
> 
> On commit 30f05309bde49295e02e45c7e615f73aa4e0ccc2.

This must be an off-by-one error.  The fix patch is below.


thanks,

Takashi

-- 8< --
From: Takashi Iwai <tiwai@xxxxxxx>
Subject: [PATCH] ALSA: seq: Fix incorrect sanity check at
 snd_seq_oss_synth_cleanup()

ALSA sequencer OSS emulation code has a sanity check for currently
opened devices, but there is a thinko there, eventually it spews
warnings and skips the operation wrongly.

Fix this off-by-one error.

Reported-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Takashi Iwai <tiwai@xxxxxxx>
---
 sound/core/seq/oss/seq_oss_synth.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/sound/core/seq/oss/seq_oss_synth.c b/sound/core/seq/oss/seq_oss_synth.c
index 0f3b38184fe5..b16dbef04174 100644
--- a/sound/core/seq/oss/seq_oss_synth.c
+++ b/sound/core/seq/oss/seq_oss_synth.c
@@ -308,7 +308,7 @@ snd_seq_oss_synth_cleanup(struct seq_oss_devinfo *dp)
 	struct seq_oss_synth *rec;
 	struct seq_oss_synthinfo *info;
 
-	if (snd_BUG_ON(dp->max_synthdev >= SNDRV_SEQ_OSS_MAX_SYNTH_DEVS))
+	if (snd_BUG_ON(dp->max_synthdev > SNDRV_SEQ_OSS_MAX_SYNTH_DEVS))
 		return;
 	for (i = 0; i < dp->max_synthdev; i++) {
 		info = &dp->synths[i];
-- 
2.7.0