linux-kernel - [PATCH] ALSA: core: Fix possible null-pointer dereferences in snd_timer_proc

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Date:   Wed, 24 Jul 2019 20:13:27 +0800
From:   Jia-Ju Bai <baijiaju1990@...il.com>
To:     perex@...ex.cz, tiwai@...e.com, bhelgaas@...gle.com,
        tglx@...utronix.de, rfontana@...hat.com,
        gregkh@...uxfoundation.org, kirr@...edi.com
Cc:     alsa-devel@...a-project.org, linux-kernel@...r.kernel.org,
        Jia-Ju Bai <baijiaju1990@...il.com>
Subject: [PATCH] ALSA: core: Fix possible null-pointer dereferences in snd_timer_proc_read()

In snd_timer_proc_read(), there is an if statement on line 1204 to check
whether timer->card is NULL:
    if (timer->card && timer->card->shutdown)

When timer->card is NULL, it is used on lines 1212 and 1215:
    timer->card->number

Thus, possible null-pointer dereferences may occur.

To fix these bugs, timer->card is checked before being used.

These bugs are found by a static analysis tool STCheck written by us.

Signed-off-by: Jia-Ju Bai <baijiaju1990@...il.com>
---
 sound/core/timer.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/sound/core/timer.c b/sound/core/timer.c
index 5c9fbf3f4340..967d06a3cdec 100644
--- a/sound/core/timer.c
+++ b/sound/core/timer.c
@@ -1208,11 +1208,13 @@ static void snd_timer_proc_read(struct snd_info_entry *entry,
 			snd_iprintf(buffer, "G%i: ", timer->tmr_device);
 			break;
 		case SNDRV_TIMER_CLASS_CARD:
-			snd_iprintf(buffer, "C%i-%i: ",
-				    timer->card->number, timer->tmr_device);
+			snd_iprintf(buffer, "C%i-%i: ", 
+					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:
-- 
2.17.0