general protection fault in pppol2tp_connect

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: e917467d Merge 4.4.151 into android-4.4
git tree: android-4.4
console output: https://syzkaller.appspot.com/x/log.txt?x=1259d932400000
kernel config: https://syzkaller.appspot.com/x/.config?x=27120f78cba3e7fe
dashboard link: https://syzkaller.appspot.com/bug?extid=f9a28cbd9a1d742fa6c7
compiler: gcc (GCC) 8.0.1 20180413 (experimental)
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=13adb9bc400000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+f9a28c...@syzkaller.appspotmail.com

IPv6: ADDRCONF(NETDEV_CHANGE): veth1_to_bridge: link becomes ready
IPv6: ADDRCONF(NETDEV_UP): veth0: link is not ready
IPv6: ADDRCONF(NETDEV_CHANGE): veth0: link becomes ready
l2tp_core: tunl 4: sockfd_lookup(fd=5) returned -9
kasan: CONFIG_KASAN_INLINE enabled
kasan: GPF could be caused by NULL-ptr deref or user memory accessgeneral
protection fault: 0000 [#1] PREEMPT SMP KASAN
Dumping ftrace buffer:
(ftrace buffer empty)
Modules linked in:
CPU: 0 PID: 4460 Comm: syz-executor0 Not tainted 4.4.151-ge917467 #84
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
task: ffff8801c9f71800 task.stack: ffff8801c9f90000
RIP: 0010:[<ffffffff835adfb3>] [<ffffffff835adfb3>] __read_once_size
include/linux/compiler.h:218 [inline]
RIP: 0010:[<ffffffff835adfb3>] [<ffffffff835adfb3>] sk_dst_get
include/net/sock.h:1740 [inline]
RIP: 0010:[<ffffffff835adfb3>] [<ffffffff835adfb3>]
pppol2tp_connect+0x873/0x1910 net/l2tp/l2tp_ppp.c:762
RSP: 0018:ffff8801c9f97bc8 EFLAGS: 00010202
RAX: dffffc0000000000 RBX: ffff8800b7bdee80 RCX: 1ffffffff0942ce0
RDX: 000000000000003b RSI: ffffffff835adf9b RDI: 00000000000001d8
RBP: ffff8801c9f97d78 R08: ffff8801c9f72128 R09: 0000000000000000
R10: 0000000000000001 R11: ffff8801c9f71800 R12: ffff8801da2f5900
R13: ffff8800b7bdeeb0 R14: 0000000000000000 R15: ffff8801d658aa00
FS: 00007f40bc392700(0000) GS:ffff8801db200000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000020000180 CR3: 00000001da122000 CR4: 00000000001606f0
Stack:
ffffffff835adf3b 0000000200000005 ffff8801c9f97cd0 ffff880100000000
ffff8800b7bdf250 ffff8800b7bdee92 1ffff100393f2f82 ffff8801da2f5a98
ffff8801d658ab80 0000000041b58ab3 ffffffff8424e778 ffffffff835ad740
Call Trace:
[<ffffffff82f27758>] SYSC_connect+0x1b8/0x300 net/socket.c:1558
[<ffffffff82f2a094>] SyS_connect+0x24/0x30 net/socket.c:1539
[<ffffffff838cc125>] entry_SYSCALL_64_fastpath+0x22/0x9e
Code: fd 80 3d e0 75 45 01 00 0f 84 44 09 00 00 e8 65 66 da fd 49 8d be d8
01 00 00 48 b8 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 <80> 3c 02 00
0f 85 60 0d 00 00 4d 8b be d8 01 00 00 e8 57 c5 cc
RIP [<ffffffff835adfb3>] __read_once_size include/linux/compiler.h:218
[inline]
RIP [<ffffffff835adfb3>] sk_dst_get include/net/sock.h:1740 [inline]
RIP [<ffffffff835adfb3>] pppol2tp_connect+0x873/0x1910
net/l2tp/l2tp_ppp.c:762
RSP <ffff8801c9f97bc8>
---[ end trace 774a0a230f675e3b ]---


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