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From: Dmitry Vyukov <dvyukov@google.com>
Date: Fri, 6 Apr 2018 11:09:43 +0200
Message-ID: <CACT4Y+ZHLgS-c6uuge7wL=2zNE2_0jymiHjgaU4HgENhemczPw@mail.gmail.com>
Subject: Re: KASAN: alloca-out-of-bounds Read in unwind_next_frame
To: syzbot <syzbot+9d1d9866b0b8ee6e0a8c@syzkaller.appspotmail.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>, Josh Poimboeuf <jpoimboe@redhat.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Masami Hiramatsu <mhiramat@kernel.org>, Ingo Molnar <mingo@redhat.com>,
        syzkaller-bugs@googlegroups.com, Thomas Gleixner <tglx@linutronix.de>,
        "the arch/x86 maintainers" <x86@kernel.org>
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On Fri, Apr 6, 2018 at 2:02 AM, syzbot
<syzbot+9d1d9866b0b8ee6e0a8c@syzkaller.appspotmail.com> wrote:
> Hello,
>
> syzbot hit the following crash on upstream commit
> 06dd3dfeea60e2a6457a6aedf97afc8e6d2ba497 (Thu Apr 5 03:07:20 2018 +0000)
> Merge tag 'char-misc-4.17-rc1' of
> git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/char-misc
> syzbot dashboard link:
> https://syzkaller.appspot.com/bug?extid=9d1d9866b0b8ee6e0a8c
>
> syzkaller reproducer:
> https://syzkaller.appspot.com/x/repro.syz?id=6478299081474048
> Raw console output:
> https://syzkaller.appspot.com/x/log.txt?id=5324218015154176
> Kernel config: https://syzkaller.appspot.com/x/.config?id=216543573824217049
> compiler: gcc (GCC) 8.0.1 20180301 (experimental)
>
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+9d1d9866b0b8ee6e0a8c@syzkaller.appspotmail.com
> 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.


This looks like a false positives related to interactions between
alloca, interrupts, KASAN and -mno-red-zones. I've filed gcc bug for
this:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85230


> ==================================================================
> BUG: KASAN: alloca-out-of-bounds in __read_once_size
> include/linux/compiler.h:188 [inline]
> BUG: KASAN: alloca-out-of-bounds in unwind_next_frame.part.7+0x7ce/0x9c0
> arch/x86/kernel/unwind_frame.c:326
> Read of size 8 at addr ffff8801b05e67f8 by task syz-executor2/11326
>
> CPU: 0 PID: 11326 Comm: syz-executor2 Not tainted 4.16.0+ #1
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> Google 01/01/2011
> Call Trace:
>  <IRQ>
>  __dump_stack lib/dump_stack.c:17 [inline]
>  dump_stack+0x1b9/0x29f lib/dump_stack.c:53
>  print_address_description+0x6c/0x20b mm/kasan/report.c:256
>  kasan_report_error mm/kasan/report.c:354 [inline]
>  kasan_report.cold.7+0xac/0x2f5 mm/kasan/report.c:412
>  __asan_report_load8_noabort+0x14/0x20 mm/kasan/report.c:433
>  __read_once_size include/linux/compiler.h:188 [inline]
>  unwind_next_frame.part.7+0x7ce/0x9c0 arch/x86/kernel/unwind_frame.c:326
>  unwind_next_frame+0x3e/0x50 arch/x86/kernel/unwind_frame.c:287
>  __save_stack_trace+0x6e/0xd0 arch/x86/kernel/stacktrace.c:44
>  save_stack_trace+0x1a/0x20 arch/x86/kernel/stacktrace.c:60
>  save_stack+0x43/0xd0 mm/kasan/kasan.c:447
>  set_track mm/kasan/kasan.c:459 [inline]
>  __kasan_slab_free+0x11a/0x170 mm/kasan/kasan.c:520
>  kasan_slab_free+0xe/0x10 mm/kasan/kasan.c:527
>  __cache_free mm/slab.c:3486 [inline]
>  kmem_cache_free+0x86/0x2d0 mm/slab.c:3744
>  __d_free+0x20/0x30 fs/dcache.c:257
>  __rcu_reclaim kernel/rcu/rcu.h:178 [inline]
>  rcu_do_batch kernel/rcu/tree.c:2675 [inline]
>  invoke_rcu_callbacks kernel/rcu/tree.c:2930 [inline]
>  __rcu_process_callbacks kernel/rcu/tree.c:2897 [inline]
>  rcu_process_callbacks+0x941/0x15f0 kernel/rcu/tree.c:2914
>  __do_softirq+0x2e0/0xaf5 kernel/softirq.c:285
>  invoke_softirq kernel/softirq.c:365 [inline]
>  irq_exit+0x1d1/0x200 kernel/softirq.c:405
>  exiting_irq arch/x86/include/asm/apic.h:525 [inline]
>  smp_apic_timer_interrupt+0x17e/0x710 arch/x86/kernel/apic/apic.c:1052
>  apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:862
>  </IRQ>
> RIP: 0010:kasan_unpoison_shadow+0x1/0x50 mm/kasan/kasan.c:68
> RSP: 0018:ffff8801b05e67e8 EFLAGS: 00000202 ORIG_RAX: ffffffffffffff13
> RAX: ffff8801c1b24100 RBX: 0000000000000000 RCX: ffffffff859d4219
> RDX: 0000000000000000 RSI: 00000000000000a8 RDI: ffff8801b05e6760
> RBP: ffff8801b05e67f8 R08: ffff8801c1b24100 R09: ffffed003b6046c2
> R10: ffffed003b6046c2 R11: ffff8801db023613 R12: 0000000000000015
> R13: 0000000000000001 R14: 0000000000000016 R15: dffffc0000000000
>  constrain_params_by_rules+0xbaa/0x1410 sound/core/pcm_param_trace.h:28
>  snd_pcm_hw_refine+0x8e9/0x1180 sound/core/pcm_native.c:502
>  snd_pcm_hw_param_mask sound/core/oss/pcm_oss.c:205 [inline]
>  snd_pcm_oss_change_params+0x8ce/0x3d10 sound/core/oss/pcm_oss.c:870
>  snd_pcm_oss_make_ready+0xe3/0x140 sound/core/oss/pcm_oss.c:1127
>  snd_pcm_oss_sync.isra.27+0x24b/0x850 sound/core/oss/pcm_oss.c:1651
>  snd_pcm_oss_release+0x214/0x290 sound/core/oss/pcm_oss.c:2446
>  __fput+0x34d/0x890 fs/file_table.c:209
>  ____fput+0x15/0x20 fs/file_table.c:243
>  task_work_run+0x1e4/0x290 kernel/task_work.c:113
>  exit_task_work include/linux/task_work.h:22 [inline]
>  do_exit+0x1aee/0x2730 kernel/exit.c:865
>  do_group_exit+0x16f/0x430 kernel/exit.c:968
>  get_signal+0x886/0x1960 kernel/signal.c:2469
>  do_signal+0x90/0x2020 arch/x86/kernel/signal.c:810
>  exit_to_usermode_loop+0x28a/0x310 arch/x86/entry/common.c:162
>  prepare_exit_to_usermode arch/x86/entry/common.c:196 [inline]
>  syscall_return_slowpath arch/x86/entry/common.c:265 [inline]
>  do_syscall_64+0x792/0x9d0 arch/x86/entry/common.c:292
>  entry_SYSCALL_64_after_hwframe+0x42/0xb7
> RIP: 0033:0x4552d9
> RSP: 002b:00007fd689eb5c68 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
> RAX: 0000000000000000 RBX: 00007fd689eb66d4 RCX: 00000000004552d9
> RDX: 0000000000000000 RSI: 0000000000004c81 RDI: 000000000000000f
> RBP: 000000000072c010 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff
> R13: 000000000000027d R14: 00000000006f6c58 R15: 0000000000000002
>
> The buggy address belongs to the page:
> page:ffffea0006c17980 count:0 mapcount:0 mapping:0000000000000000
> index:0xffff8801b05e69c0
> flags: 0x2fffc0000000000()
> raw: 02fffc0000000000 0000000000000000 ffff8801b05e69c0 00000000ffffffff
> raw: dead000000000100 dead000000000200 ffff8801dad7f600 0000000000000000
> page dumped because: kasan: bad access detected
>
> Memory state around the buggy address:
>  ffff8801b05e6680: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>  ffff8801b05e6700: 00 00 00 00 00 00 00 00 00 00 00 00 ca ca ca ca
>>
>> ffff8801b05e6780: 00 00 00 00 00 00 00 00 00 00 04 cb cb cb cb cb
>
>                                                                 ^
>  ffff8801b05e6800: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>  ffff8801b05e6880: 00 00 00 00 00 f1 f1 f1 f1 00 f2 f2 f2 f2 f2 f2
> ==================================================================
>
>
> ---
> This bug is generated by a dumb bot. It may contain errors.
> See https://goo.gl/tpsmEJ for details.
> Direct all questions to syzkaller@googlegroups.com.
>
> syzbot will keep track of this bug report.
> If you forgot to add the Reported-by tag, once the fix for this bug is
> merged
> into any tree, please reply to this email with:
> #syz fix: exact-commit-title
> If you want to test a patch for this bug, please reply with:
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> and provide the patch inline or as an attachment.
> To mark this as a duplicate of another syzbot report, please reply with:
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