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Date: Thu, 7 Jun 2018 14:58:04 -0700
From: Alexei Starovoitov <alexei.starovoitov@gmail.com>
To: Matthew Wilcox <willy@infradead.org>
Cc: syzbot <syzbot+7ade6c94abb2774c0fee@syzkaller.appspotmail.com>,
        linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
        syzkaller-bugs@googlegroups.com, netdev@vger.kernel.org,
        Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>
Subject: Re: general protection fault in __vfs_write
Message-ID: <20180607215759.5jt2rin652xnrk3h@ast-mbp>
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 <20180607152846.GB27079@bombadil.infradead.org>
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On Thu, Jun 07, 2018 at 08:28:46AM -0700, Matthew Wilcox wrote:
> 
> I would suggest this is a BPF problem, not a VFS problem.
> 
> On Thu, Jun 07, 2018 at 08:19:01AM -0700, syzbot wrote:
> > Hello,
> > 
> > syzbot found the following crash on:
> > 
> > HEAD commit:    7170e6045a6a strparser: Add __strp_unpause and use it in k..
> > git tree:       net-next
> > console output: https://syzkaller.appspot.com/x/log.txt?x=14bde74f800000
> > kernel config:  https://syzkaller.appspot.com/x/.config?x=a601a80fec461d44
> > dashboard link: https://syzkaller.appspot.com/bug?extid=7ade6c94abb2774c0fee
> > compiler:       gcc (GCC) 8.0.1 20180413 (experimental)
> > 
> > Unfortunately, I don't have any reproducer for this crash yet.
> > 
> > IMPORTANT: if you fix the bug, please add the following tag to the commit:
> > Reported-by: syzbot+7ade6c94abb2774c0fee@syzkaller.appspotmail.com
> > 
> > bpfilter: read fail -512
> > kasan: GPF could be caused by NULL-ptr deref or user memory access
> > general protection fault: 0000 [#1] SMP KASAN
> > Dumping ftrace buffer:
> >    (ftrace buffer empty)
> > Modules linked in:
> > CPU: 1 PID: 4590 Comm: syz-executor7 Not tainted 4.17.0-rc7+ #82
> > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> > Google 01/01/2011
> > RIP: 0010:file_write_hint include/linux/fs.h:1925 [inline]
> > RIP: 0010:init_sync_kiocb include/linux/fs.h:1935 [inline]
> > RIP: 0010:new_sync_write fs/read_write.c:470 [inline]
> > RIP: 0010:__vfs_write+0x4a6/0x960 fs/read_write.c:487
> > RSP: 0018:ffff88019b5c7850 EFLAGS: 00010202
> > RAX: dffffc0000000000 RBX: ffff8801d2117c80 RCX: ffffffff81bfc6bb
> > RDX: 0000000000000019 RSI: ffffffff81bfc6ca RDI: 00000000000000c8
> > RBP: ffff88019b5c79c8 R08: ffff88019b5ba540 R09: fffffbfff12cae69
> > R10: ffff88019b5c7a10 R11: ffffffff8965734b R12: 0000000000000000
> > R13: ffff88019b5c79a0 R14: 0000000000000000 R15: ffff88019b5c7a88
> > FS:  0000000002a11940(0000) GS:ffff8801daf00000(0000) knlGS:0000000000000000
> > CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > CR2: 0000000000700138 CR3: 000000019b410000 CR4: 00000000001406e0
> > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> > Call Trace:
> >  __kernel_write+0x10c/0x380 fs/read_write.c:506
> >  __bpfilter_process_sockopt+0x1d8/0x35b net/bpfilter/bpfilter_kern.c:66

I think I see the problem. Will send the fix soon.