Re: general protection fault in __vfs_write

[Matthew Wilcox]

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@xxxxxxxxxxxxxxxxxxxxxxxxx
> 
> 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
>  bpfilter_mbox_request+0x4d/0xb0 net/ipv4/bpfilter/sockopt.c:25
>  bpfilter_ip_get_sockopt+0x6b/0x90 net/ipv4/bpfilter/sockopt.c:42
>  ip_getsockopt+0x238/0x2a0 net/ipv4/ip_sockglue.c:1563
>  tcp_getsockopt+0x93/0xe0 net/ipv4/tcp.c:3543
>  sock_common_getsockopt+0x9a/0xe0 net/core/sock.c:3018
>  __sys_getsockopt+0x1a5/0x370 net/socket.c:1940
>  __do_sys_getsockopt net/socket.c:1951 [inline]
>  __se_sys_getsockopt net/socket.c:1948 [inline]
>  __x64_sys_getsockopt+0xbe/0x150 net/socket.c:1948
>  do_syscall_64+0x1b1/0x800 arch/x86/entry/common.c:287
>  entry_SYSCALL_64_after_hwframe+0x49/0xbe
> RIP: 0033:0x4584ea
> RSP: 002b:0000000000a3e328 EFLAGS: 00000246 ORIG_RAX: 0000000000000037
> RAX: ffffffffffffffda RBX: 0000000000a3e350 RCX: 00000000004584ea
> RDX: 0000000000000040 RSI: 0000000000000000 RDI: 0000000000000013
> RBP: 0000000000705f20 R08: 0000000000a3e34c R09: 0000000000004000
> R10: 0000000000a3e350 R11: 0000000000000246 R12: 0000000000000013
> R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000705860
> Code: 48 c1 ea 03 80 3c 02 00 0f 85 1b 04 00 00 48 b8 00 00 00 00 00 fc ff
> df 4c 8b 63 20 49 8d bc 24 c8 00 00 00 48 89 fa 48 c1 ea 03 <0f> b6 04 02 84
> c0 74 08 3c 03 0f 8e ec 02 00 00 41 8b 84 24 c8
> RIP: file_write_hint include/linux/fs.h:1925 [inline] RSP: ffff88019b5c7850
> RIP: init_sync_kiocb include/linux/fs.h:1935 [inline] RSP: ffff88019b5c7850
> RIP: new_sync_write fs/read_write.c:470 [inline] RSP: ffff88019b5c7850
> RIP: __vfs_write+0x4a6/0x960 fs/read_write.c:487 RSP: ffff88019b5c7850
> ---[ end trace 556c3fc867e1de54 ]---
> 
> 
> ---
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