linux-kernel - [PATCH] ALSA: control: fix memory leak in snd_ctl_elem_read

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Date: Thu, 21 Mar 2024 12:17:00 -0400
From: Johannes Weiner <hannes@...xchg.org>
To: Takashi Iwai <tiwai@...e.com>
Cc: Jaroslav Kysela <perex@...ex.cz>,
	linux-sound@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH] ALSA: control: fix memory leak in snd_ctl_elem_read_user()

With 6.9, I noticed kmalloc-2k blowing up to tens of gigabytes over
several days. Kmemleak shows a long string of these:

unreferenced object 0xffff8f1bddbce800 (size 2048):
  comm "wireplumber", pid 1058, jiffies 4294690193
  hex dump (first 32 bytes):
    14 00 00 00 02 00 00 00 00 00 00 00 00 00 00 00  ................
    4d 61 73 74 65 72 20 50 6c 61 79 62 61 63 6b 20  Master Playback
  backtrace (crc bd965d91):
    [<ffffffff85ac328b>] __kmalloc_node_track_caller+0x25b/0x370
    [<ffffffff85a79375>] memdup_user+0x25/0x80
    [<ffffffff85fa5d63>] snd_ctl_ioctl+0x753/0x880
    [<ffffffff85b18119>] __x64_sys_ioctl+0x89/0xb0
    [<ffffffff861ee190>] do_syscall_64+0x80/0x170
    [<ffffffff862000ab>] entry_SYSCALL_64_after_hwframe+0x46/0x4e

When 1052d9882269 ("ALSA: control: Use automatic cleanup of kfree()")
converted a few sites to automatic freeing, it removed the kfree from
snd_ctl_elem_read_user() but forgot to add the __free hook.

Fixes: 1052d9882269 ("ALSA: control: Use automatic cleanup of kfree()")
Signed-off-by: Johannes Weiner <hannes@...xchg.org>
---
 sound/core/control.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/sound/core/control.c b/sound/core/control.c
index 8367fd485371..7da0d6afb766 100644
--- a/sound/core/control.c
+++ b/sound/core/control.c
@@ -1275,7 +1275,7 @@ static int snd_ctl_elem_read(struct snd_card *card,
 static int snd_ctl_elem_read_user(struct snd_card *card,
 				  struct snd_ctl_elem_value __user *_control)
 {
-	struct snd_ctl_elem_value *control;
+	struct snd_ctl_elem_value *control __free(kfree) = NULL;
 	int result;
 
 	control = memdup_user(_control, sizeof(*control));
-- 
2.44.0