On Fri, 27 Oct 2017 10:34:01 +0200, syzbot wrote: > > Hello, > > syzkaller hit the following crash on > 33d930e59a98fa10a0db9f56c7fa2f21a4aef9b9 > git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/master > compiler: gcc (GCC) 7.1.1 20170620 > .config is attached > Raw console output is attached. > > syzkaller reproducer is attached. See https://goo.gl/kgGztJ > for information about syzkaller reproducers > > > BUG: KASAN: use-after-free in > snd_timer_user_info_compat.isra.6+0x46c/0x480 > sound/core/timer_compat.c:71 > Read of size 8 at addr ffff8801d0dd9d00 by task syz-executor0/3342 OK, this is a real bug, and obviously a forgotten code path from the previous fixes. The patch below should address it, but I checked only compile-tested, so far. Let me know if it really works. thanks, Takashi -- 8< -- From: Takashi Iwai <tiwai@xxxxxxx> Subject: [PATCH] ALSA: timer: Add missing mutex lock for compat ioctls The races among ioctl and other operations were protected by the commit af368027a49a ("ALSA: timer: Fix race among timer ioctls") and later fixes, but one code path was forgotten in the scenario: the 32bit compat ioctl. As syzkaller recently spotted, a very similar use-after-free may happen with the combination of compat ioctls. The fix is simply to apply the same ioctl_lock to the compat_ioctl callback, too. Fixes: af368027a49a ("ALSA: timer: Fix race among timer ioctls") Reference: http://lkml.kernel.org/r/089e082686ac9b482e055c832617@xxxxxxxxxx Reported-by: syzbot <bot+e5f3c9783e7048a74233054febbe9f1bdf54b6da@xxxxxxxxxxxxxxxxxxxxxxxxx> Cc: <stable@xxxxxxxxxxxxxxx> Signed-off-by: Takashi Iwai <tiwai@xxxxxxx> --- sound/core/timer_compat.c | 17 +++++++++++++++-- 1 file changed, 15 insertions(+), 2 deletions(-) diff --git a/sound/core/timer_compat.c b/sound/core/timer_compat.c index 6a437eb66115..59127b6ef39e 100644 --- a/sound/core/timer_compat.c +++ b/sound/core/timer_compat.c @@ -133,7 +133,8 @@ enum { #endif /* CONFIG_X86_X32 */ }; -static long snd_timer_user_ioctl_compat(struct file *file, unsigned int cmd, unsigned long arg) +static long __snd_timer_user_ioctl_compat(struct file *file, unsigned int cmd, + unsigned long arg) { void __user *argp = compat_ptr(arg); @@ -153,7 +154,7 @@ static long snd_timer_user_ioctl_compat(struct file *file, unsigned int cmd, uns case SNDRV_TIMER_IOCTL_PAUSE: case SNDRV_TIMER_IOCTL_PAUSE_OLD: case SNDRV_TIMER_IOCTL_NEXT_DEVICE: - return snd_timer_user_ioctl(file, cmd, (unsigned long)argp); + return __snd_timer_user_ioctl(file, cmd, (unsigned long)argp); case SNDRV_TIMER_IOCTL_GPARAMS32: return snd_timer_user_gparams_compat(file, argp); case SNDRV_TIMER_IOCTL_INFO32: @@ -167,3 +168,15 @@ static long snd_timer_user_ioctl_compat(struct file *file, unsigned int cmd, uns } return -ENOIOCTLCMD; } + +static long snd_timer_user_ioctl_compat(struct file *file, unsigned int cmd, + unsigned long arg) +{ + struct snd_timer_user *tu = file->private_data; + long ret; + + mutex_lock(&tu->ioctl_lock); + ret = __snd_timer_user_ioctl_compat(file, cmd, arg); + mutex_unlock(&tu->ioctl_lock); + return ret; +} -- 2.14.2 _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
