Re: BUG: unable to handle kernel NULL pointer dereference in corrupted (5)

[Takashi Iwai]

On Sat, 14 Mar 2020 07:37:13 +0100,
syzbot wrote:
> 
> Hello,
> 
> syzbot found the following crash on:
> 
> HEAD commit:    30bb5572 Merge tag 'ktest-v5.6' of git://git.kernel.org/pu..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=15d300b1e00000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=a5295e161cd85b82
> dashboard link: https://syzkaller.appspot.com/bug?extid=8b0e78e390d1715b0f4e
> compiler:       clang version 10.0.0 (https://github.com/llvm/llvm-project/ c2443155a0fb245c8f17f2c1c72b6ea391e86e81)
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=11a57709e00000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=13de9e91e00000
> 
> The bug was bisected to:
> 
> commit 271213ef4d0d3a3b80d4cf95c5f2bebb5643e666
> Author: Takashi Iwai <tiwai@xxxxxxx>
> Date:   Tue Dec 10 06:34:50 2019 +0000
> 
>     ALSA: pcxhr: Support PCM sync_stop

This must be a false-positive.
The config doesn't contain CONFIG_SND_PCXHR and this commit changes
only sound/pci/pcxhr.c.


thanks,

Takashi

> 
> bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=1566b08de00000
> final crash:    https://syzkaller.appspot.com/x/report.txt?x=1766b08de00000
> console output: https://syzkaller.appspot.com/x/log.txt?x=1366b08de00000
> 
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+8b0e78e390d1715b0f4e@xxxxxxxxxxxxxxxxxxxxxxxxx
> Fixes: 271213ef4d0d ("ALSA: pcxhr: Support PCM sync_stop")
> 
> BUG: kernel NULL pointer dereference, address: 0000000000000086
> #PF: supervisor instruction fetch in kernel mode
> #PF: error_code(0x0010) - not-present page
> PGD a27fa067 P4D a27fa067 PUD a2185067 PMD 0 
> Oops: 0010 [#1] PREEMPT SMP KASAN
> CPU: 1 PID: 9168 Comm: syz-executor418 Not tainted 5.6.0-rc5-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> RIP: 0010:0x86
> Code: Bad RIP value.
> RSP: 0018:ffffc90002c9f998 EFLAGS: 00010086
> RAX: ffffc90002c9f9c8 RBX: fffffe0000000000 RCX: ffff8880a31b6280
> RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000000
> RBP: 0000000000000ec0 R08: ffffffff839888d3 R09: ffffffff811c7d9a
> R10: ffff8880a31b6280 R11: 0000000000000002 R12: dffffc0000000000
> R13: fffffe0000000ec8 R14: ffffffff880016f0 R15: fffffe0000000ecb
> FS:  0000000000981880(0000) GS:ffff8880ae900000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 000000000000005c CR3: 00000000986d2000 CR4: 00000000001426e0
> Call Trace:
> Modules linked in:
> CR2: 0000000000000086
> ---[ end trace 7c78bc94cfc0a37d ]---
> RIP: 0010:0x86
> Code: Bad RIP value.
> RSP: 0018:ffffc90002c9f998 EFLAGS: 00010086
> RAX: ffffc90002c9f9c8 RBX: fffffe0000000000 RCX: ffff8880a31b6280
> RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000000
> RBP: 0000000000000ec0 R08: ffffffff839888d3 R09: ffffffff811c7d9a
> R10: ffff8880a31b6280 R11: 0000000000000002 R12: dffffc0000000000
> R13: fffffe0000000ec8 R14: ffffffff880016f0 R15: fffffe0000000ecb
> FS:  0000000000981880(0000) GS:ffff8880ae900000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 000000000000005c CR3: 00000000986d2000 CR4: 00000000001426e0
> 
> 
> ---
> This bug is generated by a bot. It may contain errors.
> See https://goo.gl/tpsmEJ for more information about syzbot.
> syzbot engineers can be reached at syzkaller@xxxxxxxxxxxxxxxxx
> 
> syzbot will keep track of this bug report. See:
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> For information about bisection process see: https://goo.gl/tpsmEJ#bisection
> syzbot can test patches for this bug, for details see:
> https://goo.gl/tpsmEJ#testing-patches
>