Re: KASAN: null-ptr-deref Write in linear_transfer

[Eric Biggers]

On Wed, Jan 10, 2018 at 10:58:43AM +0100, Takashi Iwai wrote:
> On Wed, 10 Jan 2018 09:08:00 +0100,
> Eric Biggers wrote:
> > 
> > On Fri, Jan 05, 2018 at 02:58:02AM -0800, syzbot wrote:
> > > Hello,
> > > 
> > > syzkaller hit the following crash on
> > > 30a7acd573899fd8b8ac39236eff6468b195ac7d
> > > 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.
> > > C reproducer is attached
> > > syzkaller reproducer is attached. See https://goo.gl/kgGztJ
> > > for information about syzkaller reproducers
> > > 
> > > 
> > > IMPORTANT: if you fix the bug, please add the following tag to the commit:
> > > Reported-by: syzbot+a8f5641f452c7e6abf03@xxxxxxxxxxxxxxxxxxxxxxxxx
> > > It will help syzbot understand when the bug is fixed. See footer for
> > > details.
> > > If you forward the report, please keep this part and the footer.
> > > 
> > > ==================================================================
> > > BUG: KASAN: null-ptr-deref in memcpy include/linux/string.h:344 [inline]
> > > BUG: KASAN: null-ptr-deref in do_convert sound/core/oss/linear.c:52 [inline]
> > > BUG: KASAN: null-ptr-deref in convert sound/core/oss/linear.c:81 [inline]
> > > BUG: KASAN: null-ptr-deref in linear_transfer+0x634/0x900
> > > sound/core/oss/linear.c:110
> > > Write of size 2 at addr           (null) by task syzkaller360172/7860
> > > 
> > > CPU: 0 PID: 7860 Comm: syzkaller360172 Not tainted 4.15.0-rc6+ #155
> > > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> > > Google 01/01/2011
> > > Call Trace:
> > >  __dump_stack lib/dump_stack.c:17 [inline]
> > >  dump_stack+0x194/0x257 lib/dump_stack.c:53
> > >  kasan_report_error mm/kasan/report.c:349 [inline]
> > >  kasan_report+0x13b/0x340 mm/kasan/report.c:409
> > >  check_memory_region_inline mm/kasan/kasan.c:260 [inline]
> > >  check_memory_region+0x137/0x190 mm/kasan/kasan.c:267
> > >  memcpy+0x37/0x50 mm/kasan/kasan.c:303
> > >  memcpy include/linux/string.h:344 [inline]
> > >  do_convert sound/core/oss/linear.c:52 [inline]
> > >  convert sound/core/oss/linear.c:81 [inline]
> > >  linear_transfer+0x634/0x900 sound/core/oss/linear.c:110
> > >  snd_pcm_plug_write_transfer+0x22d/0x420 sound/core/oss/pcm_plugin.c:611
> > >  snd_pcm_oss_write2+0x260/0x420 sound/core/oss/pcm_oss.c:1311
> > >  snd_pcm_oss_sync1+0x1cc/0x550 sound/core/oss/pcm_oss.c:1530
> > >  snd_pcm_oss_sync+0x5b6/0x830 sound/core/oss/pcm_oss.c:1604
> > >  snd_pcm_oss_release+0x20b/0x280 sound/core/oss/pcm_oss.c:2431
> > >  __fput+0x327/0x7e0 fs/file_table.c:210
> > >  ____fput+0x15/0x20 fs/file_table.c:244
> > >  task_work_run+0x199/0x270 kernel/task_work.c:113
> > >  exit_task_work include/linux/task_work.h:22 [inline]
> > >  do_exit+0x9bb/0x1ad0 kernel/exit.c:865
> > >  do_group_exit+0x149/0x400 kernel/exit.c:968
> > >  get_signal+0x73f/0x16c0 kernel/signal.c:2335
> > >  do_signal+0x90/0x1eb0 arch/x86/kernel/signal.c:809
> > >  exit_to_usermode_loop+0x214/0x310 arch/x86/entry/common.c:158
> > >  prepare_exit_to_usermode arch/x86/entry/common.c:195 [inline]
> > >  syscall_return_slowpath arch/x86/entry/common.c:264 [inline]
> > >  do_syscall_32_irqs_on arch/x86/entry/common.c:333 [inline]
> > >  do_fast_syscall_32+0xbfd/0xf9d arch/x86/entry/common.c:389
> > >  entry_SYSENTER_compat+0x54/0x63 arch/x86/entry/entry_64_compat.S:129
> > 
> > Still reproducible even after all the fixes currently in sound/for-linus.
> 
> Interesting, I can't reproduce it on my VM any longer...
> 

No longer occurring, last occurrence was Mar 29 on commit a2601d78b77aa.
Seems to have been fixed by commit 02a5d6925cd3:

#syz fix: ALSA: pcm: Avoid potential races between OSS ioctls and read/write

The reproducer was opening /dev/dsp1, then concurrently writing to it and
calling the SNDCTL_DSP_SPEED ioctl.

- Eric