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

[Eric Biggers]

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.

Eric