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

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Message-ID: <20251103114902.11423-2-hariconscious@gmail.com>
Date: Mon,  3 Nov 2025 17:19:03 +0530
From: hariconscious@...il.com
To: perex@...ex.cz,
	tiwai@...e.com
Cc: 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,
	HariKrishna Sagala <hariconscious@...il.com>
Subject: [PATCH] ALSA: timer: Fix null dereference of 'timer->card' reported by smatch

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).

 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