On Sun, Oct 29, 2017 at 11:10 AM, Takashi Iwai <tiwai@xxxxxxx> wrote: > 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; > +} #syz fix: ALSA: timer: Add missing mutex lock for compat ioctls _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
