linux-kernel - Re: [PATCH] ALSA: timer: Fix null dereference of 'timer->card' reported by smatch

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Message-ID: <875xbqi0tc.wl-tiwai@suse.de>
Date: Tue, 04 Nov 2025 10:50:23 +0100
From: Takashi Iwai <tiwai@...e.de>
To: hariconscious@...il.com
Cc: perex@...ex.cz,
	tiwai@...e.com,
	khalid@...nel.org,
	shuah@...nel.org,
	david.hunter.linux@...il.com,
	mingo@...nel.org,
	tglx@...utronix.de,
	thorsten.blum@...ux.dev,
	mengdewei@...oftware.com.cn,
	linux-sound@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ALSA: timer: Fix null dereference of 'timer->card' reported by smatch

On Mon, 03 Nov 2025 12:49:03 +0100,
hariconscious@...il.com wrote:
> 
> From: HariKrishna Sagala <hariconscious@...il.com>
> 
> Fix null dereference in snd_timer_proc_read().
> 
> Smatch reported that  was previously assumed to be null
> at line 1226, but later accessed without a check.
> This could lead to a null pointer dereference under certain conditions.
> 
> Add a null check before accessing to ensure safe execution.
> 
> Signed-off-by: HariKrishna Sagala <hariconscious@...il.com>
> ---
> This patch addresses a null pointer dereference in snd_timer_proc_read()
> by adding a proper check for timer->card.The issue was flagged by Smatch,
> which noted that timer->card was previously assumed to be null at
> line 1226 but accessed without validation.To ensure safe access, a
> conditional check has been introduced before referencing timer->card.
> The fix was verified by booting the kernel and performing audio playback
> using ALSA commands. Additionally, the /proc/asound/timers
> interface was inspected to confirm that timer information is
> correctly populated and accessible without errors.
> Note: Couldn't simulate a scenario where 'timer->card' is null and
> 'timer->card->shutdown' is 1 (shutdown initiated).

timer->card is guaranteed to be non-NULL for SNDRV_TIMER_CLASS_CARD
timer->and SNDRV_TIMER_CLASS_PCM at the creation in snd_timer_new().
So this check is superfluous.


thanks,

Takashi

> 
>  sound/core/timer.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/sound/core/timer.c b/sound/core/timer.c
> index d9fff5c87613..d65e8bcb2f46 100644
> --- a/sound/core/timer.c
> +++ b/sound/core/timer.c
> @@ -1231,10 +1231,11 @@ static void snd_timer_proc_read(struct snd_info_entry *entry,
>  			break;
>  		case SNDRV_TIMER_CLASS_CARD:
>  			snd_iprintf(buffer, "C%i-%i: ",
> -				    timer->card->number, timer->tmr_device);
> +				    timer->card ? timer->card->number : -1, timer->tmr_device);
>  			break;
>  		case SNDRV_TIMER_CLASS_PCM:
> -			snd_iprintf(buffer, "P%i-%i-%i: ", timer->card->number,
> +			snd_iprintf(buffer, "P%i-%i-%i: ",
> +				    timer->card ? timer->card->number : -1,
>  				    timer->tmr_device, timer->tmr_subdevice);
>  			break;
>  		default:
> 
> base-commit: 6093a688a07da07808f0122f9aa2a3eed250d853
> -- 
> 2.43.0
>