Re: WARNING in ion_buffer_destroy

[Laura Abbott]

On 01/09/2018 02:58 PM, syzbot wrote:
> Hello,
>
> syzkaller hit the following crash on 06d41862286aa7bc634a1dd9e6e7e96f925ef30a
> git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.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+cd8bcd40cb049efa2770@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.
>
> audit: type=1400 audit(1515538424.230:7): avc: denied { map } for pid=3499 comm="syzkaller239906" path="/root/syzkaller239906633" dev="sda1" ino=16481 scontext=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023 tcontext=unconfined_u:object_r:user_home_t:s0 tclass=file permissive=1
> WARNING: CPU: 0 PID: 1467 at drivers/staging/android/ion/ion.c:122 ion_buffer_destroy+0xd4/0x190 drivers/staging/android/ion/ion.c:122
> Kernel panic - not syncing: panic_on_warn set ...
>
> CPU: 0 PID: 1467 Comm: ion_system_heap Not tainted 4.15.0-rc7-next-20180109+ #92
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> Call Trace:
>  Â__dump_stack lib/dump_stack.c:17 [inline]
>  Âdump_stack+0x194/0x257 lib/dump_stack.c:53
>  Âpanic+0x1e4/0x41c kernel/panic.c:183
>  Â__warn+0x1dc/0x200 kernel/panic.c:547
>  Âreport_bug+0x211/0x2d0 lib/bug.c:184
>  Âfixup_bug.part.11+0x37/0x80 arch/x86/kernel/traps.c:178
>  Âfixup_bug arch/x86/kernel/traps.c:247 [inline]
>  Âdo_error_trap+0x2d7/0x3e0 arch/x86/kernel/traps.c:296
>  Âdo_invalid_op+0x1b/0x20 arch/x86/kernel/traps.c:315
>  Âinvalid_op+0x22/0x40 arch/x86/entry/entry_64.S:1079
> RIP: 0010:ion_buffer_destroy+0xd4/0x190 drivers/staging/android/ion/ion.c:122
> RSP: 0018:ffff8801d3a9fd28 EFLAGS: 00010293
> RAX: ffff8801d39ee700 RBX: ffff8801c00e57c0 RCX: ffffffff8415d2a4
> RDX: 0000000000000000 RSI: 0000000000000001 RDI: ffff8801d5ada5b8
> RBP: ffff8801d3a9fd50 R08: 0000000000000000 R09: 1ffff1003a753f8a
> R10: ffff8801d3a9fc18 R11: 0000000000000000 R12: ffffffff86e4c980
> R13: ffff8801d5ada580 R14: ffff8801c00e57e0 R15: 0000000000000001
>  Âion_heap_deferred_free+0x290/0x650 drivers/staging/android/ion/ion_heap.c:236
>  Âkthread+0x33c/0x400 kernel/kthread.c:238
>  Âret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:524
> Dumping ftrace buffer:
>  ÂÂ (ftrace buffer empty)
> Kernel Offset: disabled
> Rebooting in 86400 seconds..

This is catching that a buffer was freed with an existing kernel
map still present. The problem is this can easily be triggered from
userspace by calling DMA_BUF_SYNC_START without calling
DMA_BUF_SYNC_END. It's clearly not appropriate for userspace to
be able to trigger a warning so I'll see about switching this to
a pr_warn_once.

Thanks,
Laura