Re: [PATCH] ALSA: timer: fix ida_free call while not allocated

[Takashi Iwai <tiwai@xxxxxxx>]

On Thu, 21 Aug 2025 03:43:17 +0200,
Dewei Meng wrote:
> 
> 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@xxxxxxxxxxxxxxxxx>

Applied now.  Thanks.


Takashi