linux-kernel - [PATCH] ALSA: timer: fix ida_free call while not allocated

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Message-ID: <20250821014317.40786-1-mengdewei@cqsoftware.com.cn>
Date: Thu, 21 Aug 2025 09:43:17 +0800
From: Dewei Meng <mengdewei@...oftware.com.cn>
To: perex@...ex.cz,
	tiwai@...e.com
Cc: linux-sound@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	ivan.orlov0322@...il.com,
	Dewei Meng <mengdewei@...oftware.com.cn>
Subject: [PATCH] ALSA: timer: fix ida_free call while not allocated

In the snd_utimer_create() function, if the kasprintf() function return
NULL, snd_utimer_put_id() will be called, finally use ida_free()
to free the unallocated id 0.

the syzkaller reported the following information:
  ------------[ cut here ]------------
  ida_free called for id=0 which is not allocated.
  WARNING: CPU: 1 PID: 1286 at lib/idr.c:592 ida_free+0x1fd/0x2f0 lib/idr.c:592
  Modules linked in:
  CPU: 1 UID: 0 PID: 1286 Comm: syz-executor164 Not tainted 6.15.8 #3 PREEMPT(lazy)
  Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.3-4.fc42 04/01/2014
  RIP: 0010:ida_free+0x1fd/0x2f0 lib/idr.c:592
  Code: f8 fc 41 83 fc 3e 76 69 e8 70 b2 f8 (...)
  RSP: 0018:ffffc900007f79c8 EFLAGS: 00010282
  RAX: 0000000000000000 RBX: 1ffff920000fef3b RCX: ffffffff872176a5
  RDX: ffff88800369d200 RSI: 0000000000000000 RDI: ffff88800369d200
  RBP: 0000000000000000 R08: ffffffff87ba60a5 R09: 0000000000000000
  R10: 0000000000000001 R11: 0000000000000000 R12: 0000000000000000
  R13: 0000000000000002 R14: 0000000000000000 R15: 0000000000000000
  FS:  00007f6f1abc1740(0000) GS:ffff8880d76a0000(0000) knlGS:0000000000000000
  CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
  CR2: 00007f6f1ad7a784 CR3: 000000007a6e2000 CR4: 00000000000006f0
  Call Trace:
   <TASK>
   snd_utimer_put_id sound/core/timer.c:2043 [inline] [snd_timer]
   snd_utimer_create+0x59b/0x6a0 sound/core/timer.c:2184 [snd_timer]
   snd_utimer_ioctl_create sound/core/timer.c:2202 [inline] [snd_timer]
   __snd_timer_user_ioctl.isra.0+0x724/0x1340 sound/core/timer.c:2287 [snd_timer]
   snd_timer_user_ioctl+0x75/0xc0 sound/core/timer.c:2298 [snd_timer]
   vfs_ioctl fs/ioctl.c:51 [inline]
   __do_sys_ioctl fs/ioctl.c:907 [inline]
   __se_sys_ioctl fs/ioctl.c:893 [inline]
   __x64_sys_ioctl+0x198/0x200 fs/ioctl.c:893
   do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
   do_syscall_64+0x7b/0x160 arch/x86/entry/syscall_64.c:94
   entry_SYSCALL_64_after_hwframe+0x76/0x7e
  [...]

The utimer->id should be set properly before the kasprintf() function,
ensures the snd_utimer_put_id() function will free the allocated id.

Fixes: 37745918e0e75 ("ALSA: timer: Introduce virtual userspace-driven timers")
Signed-off-by: Dewei Meng <mengdewei@...oftware.com.cn>
---
 sound/core/timer.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/sound/core/timer.c b/sound/core/timer.c
index 3ce12264eed8..d9fff5c87613 100644
--- a/sound/core/timer.c
+++ b/sound/core/timer.c
@@ -2139,14 +2139,14 @@ static int snd_utimer_create(struct snd_timer_uinfo *utimer_info,
 		goto err_take_id;
 	}
 
+	utimer->id = utimer_id;
+
 	utimer->name = kasprintf(GFP_KERNEL, "snd-utimer%d", utimer_id);
 	if (!utimer->name) {
 		err = -ENOMEM;
 		goto err_get_name;
 	}
 
-	utimer->id = utimer_id;
-
 	tid.dev_sclass = SNDRV_TIMER_SCLASS_APPLICATION;
 	tid.dev_class = SNDRV_TIMER_CLASS_GLOBAL;
 	tid.card = -1;
-- 
2.43.5