linux-kernel - Re: [PATCH -next] ALSA: seq: fix undefined behavior in bit shift for SNDRV_SEQ_FILTER_USE

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Date:   Mon, 21 Nov 2022 11:35:41 +0100
From:   Takashi Iwai <tiwai@...e.de>
To:     Baisong Zhong <zhongbaisong@...wei.com>
Cc:     <linux-kernel@...r.kernel.org>, <alsa-devel@...a-project.org>,
        <perex@...ex.cz>, <tiwai@...e.com>
Subject: Re: [PATCH -next] ALSA: seq: fix undefined behavior in bit shift for SNDRV_SEQ_FILTER_USE_EVENT

On Mon, 21 Nov 2022 05:36:25 +0100,
Baisong Zhong wrote:
> 
> Shifting signed 32-bit value by 31 bits is undefined, so changing
> significant bit to unsigned. The UBSAN warning calltrace like below:
> 
> UBSAN: shift-out-of-bounds in sound/core/seq/seq_clientmgr.c:509:22
> left shift of 1 by 31 places cannot be represented in type 'int'
> ...
> Call Trace:
>  <TASK>
>  dump_stack_lvl+0x8d/0xcf
>  ubsan_epilogue+0xa/0x44
>  __ubsan_handle_shift_out_of_bounds+0x1e7/0x208
>  snd_seq_deliver_single_event.constprop.21+0x191/0x2f0
>  snd_seq_deliver_event+0x1a2/0x350
>  snd_seq_kernel_client_dispatch+0x8b/0xb0
>  snd_seq_client_notify_subscription+0x72/0xa0
>  snd_seq_ioctl_subscribe_port+0x128/0x160
>  snd_seq_kernel_client_ctl+0xce/0xf0
>  snd_seq_oss_create_client+0x109/0x15b
>  alsa_seq_oss_init+0x11c/0x1aa
>  do_one_initcall+0x80/0x440
>  kernel_init_freeable+0x370/0x3c3
>  kernel_init+0x1b/0x190
>  ret_from_fork+0x1f/0x30
>  </TASK>
> 
> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> Signed-off-by: Baisong Zhong <zhongbaisong@...wei.com>
> ---
>  include/uapi/sound/asequencer.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/include/uapi/sound/asequencer.h b/include/uapi/sound/asequencer.h
> index 6d4a2c60808d..4c5c4dd15d02 100644
> --- a/include/uapi/sound/asequencer.h
> +++ b/include/uapi/sound/asequencer.h
> @@ -331,7 +331,7 @@ typedef int __bitwise snd_seq_client_type_t;
>  #define SNDRV_SEQ_FILTER_BROADCAST	(1<<0)	/* accept broadcast messages */
>  #define SNDRV_SEQ_FILTER_MULTICAST	(1<<1)	/* accept multicast messages */
>  #define SNDRV_SEQ_FILTER_BOUNCE		(1<<2)	/* accept bounce event in error */
> -#define SNDRV_SEQ_FILTER_USE_EVENT	(1<<31)	/* use event filter */
> +#define SNDRV_SEQ_FILTER_USE_EVENT	(1U<<31)	/* use event filter */

Similarly like the previous patch for PCM, could you update all
SNDRV_SEQ_FILTER_* to 1U for consistency?


thanks,

Takashi