general protection fault in strlen

[syzbot]

Hello,

syzbot hit the following crash on upstream commit
8cbab92dff778e516064c13113ca15d4869ec883

So far this crash happened 19 times on linux-next, net-next, upstream.
C reproducer is attached.
syzkaller reproducer is attached.
Raw console output is attached.
compiler: gcc (GCC) 7.1.1 20170620
.config is attached.

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Reported-by: syzbot+6e1398...@syzkaller.appspotmail.com
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kasan: CONFIG_KASAN_INLINE enabled
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: 28718 Comm: syzkaller365228 Not tainted 4.15.0-rc8+ #265
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
RIP: 0010:strlen+0x1f/0xa0 lib/string.c:479
RSP: 0018:ffff8801c062f760 EFLAGS: 00010286
RAX: 0000000000000004 RBX: ffff8801cc392800 RCX: 0000000000000000
RDX: dffffc0000000000 RSI: ffff8801d57d7680 RDI: 0000000000000004
RBP: ffff8801c062f778 R08: ffffffff84adf590 R09: 0000000000000004
R10: ffff8801c062f920 R11: 0000000000000004 R12: ffff8801c062f898
R13: 0000000000000004 R14: 0000000000000040 R15: 1ffff100380c5ef7
FS: 00007f11d32d8700(0000) GS:ffff8801db300000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007ffeee3b49d4 CR3: 00000001caead001 CR4: 00000000001606e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
strlen include/linux/string.h:266 [inline]
netlink_ack+0x120/0xa10 net/netlink/af_netlink.c:2324
netlink_rcv_skb+0x2d1/0x400 net/netlink/af_netlink.c:2415
xfrm_netlink_rcv+0x6f/0x90 net/xfrm/xfrm_user.c:2599
netlink_unicast_kernel net/netlink/af_netlink.c:1275 [inline]
netlink_unicast+0x4ee/0x700 net/netlink/af_netlink.c:1301
netlink_sendmsg+0xa4a/0xe60 net/netlink/af_netlink.c:1864
sock_sendmsg_nosec net/socket.c:638 [inline]
sock_sendmsg+0xca/0x110 net/socket.c:648
___sys_sendmsg+0x767/0x8b0 net/socket.c:2028
__sys_sendmsg+0xe5/0x210 net/socket.c:2062
SYSC_sendmsg net/socket.c:2073 [inline]
SyS_sendmsg+0x2d/0x50 net/socket.c:2069
entry_SYSCALL_64_fastpath+0x29/0xa0
RIP: 0033:0x44c569
RSP: 002b:00007f11d32d7ce8 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00000000006dec24 RCX: 000000000044c569
RDX: 0000000000000000 RSI: 0000000020f1efc8 RDI: 0000000000000004
RBP: 00000000006dec20 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007ffeee3b48af R14: 00007f11d32d89c0 R15: 0000000000000004
Code: 37 ff ff ff 0f 1f 84 00 00 00 00 00 55 48 89 f9 48 ba 00 00 00 00 00
fc ff df 48 c1 e9 03 48 89 f8 48 89 e5 41 54 53 48 83 ec 08 <0f> b6 14 11
48 89 f9 83 e1 07 38 ca 7f 04 84 d2 75 4b 80 38 00
RIP: strlen+0x1f/0xa0 lib/string.c:479 RSP: ffff8801c062f760
---[ end trace ecfeb6e4224e1ee8 ]---
Kernel panic - not syncing: Fatal exception
Dumping ftrace buffer:
(ftrace buffer empty)
Kernel Offset: disabled
Rebooting in 86400 seconds..


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[Xin Long]

This patch will also fix it:
https://patchwork.ozlabs.org/patch/862778/

[Dmitry Vyukov]

On Thu, Jan 18, 2018 at 6:54 PM, Xin Long <lucie...@gmail.com> wrote:
> This patch will also fix it:
> https://patchwork.ozlabs.org/patch/862778/

#syz fix: netlink: reset extack earlier in netlink_rcv_skb