general protection fault in erspan_netlink_parms

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: 0fda7600 geneve: move debug check after netdev unregister
git tree: net
console output: https://syzkaller.appspot.com/x/log.txt?x=134e9555e00000
kernel config: https://syzkaller.appspot.com/x/.config?x=c2e311dba9a02ba9
dashboard link: https://syzkaller.appspot.com/bug?extid=1b4ebf4dae4e510dd219
compiler: gcc (GCC) 9.0.0 20181231 (experimental)
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1627f955e00000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=111ac52de00000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+1b4ebf...@syzkaller.appspotmail.com

netlink: 4 bytes leftover after parsing attributes in process `syz-executor042'.
general protection fault, probably for non-canonical address 0xdffffc0000000016: 0000 [#1] PREEMPT SMP KASAN
KASAN: null-ptr-deref in range [0x00000000000000b0-0x00000000000000b7]
CPU: 0 PID: 9887 Comm: syz-executor042 Not tainted 5.6.0-rc5-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
RIP: 0010:erspan_netlink_parms.isra.0+0x5c/0x420 net/ipv4/ip_gre.c:1172
Code: 6a 03 d6 fa 45 85 e4 0f 85 f0 00 00 00 e8 ec 01 d6 fa 48 8d bb b0 00 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 37 03 00 00 4c 8b ab b0 00 00 00 4d 85 ed 0f 84
RSP: 0018:ffffc90001f17080 EFLAGS: 00010202
RAX: dffffc0000000000 RBX: 0000000000000000 RCX: ffffffff869c13c6
RDX: 0000000000000016 RSI: ffffffff869c13d4 RDI: 00000000000000b0
RBP: ffff888090c0a000 R08: ffff88809a4f6240 R09: ffffc90001f170f0
R10: fffff520003e2e24 R11: 0000000000000003 R12: 0000000000000000
R13: ffffc90001f170e0 R14: 0000000000000000 R15: ffffc90001f17428
FS: 0000000001941880(0000) GS:ffff8880ae600000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000020000284 CR3: 000000009e80a000 CR4: 00000000001406f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
erspan_newlink+0x106/0x140 net/ipv4/ip_gre.c:1341
__rtnl_newlink+0xf18/0x1590 net/core/rtnetlink.c:3319
rtnl_newlink+0x64/0xa0 net/core/rtnetlink.c:3377
rtnetlink_rcv_msg+0x44e/0xad0 net/core/rtnetlink.c:5436
netlink_rcv_skb+0x15a/0x410 net/netlink/af_netlink.c:2478
netlink_unicast_kernel net/netlink/af_netlink.c:1303 [inline]
netlink_unicast+0x537/0x740 net/netlink/af_netlink.c:1329
netlink_sendmsg+0x882/0xe10 net/netlink/af_netlink.c:1918
sock_sendmsg_nosec net/socket.c:652 [inline]
sock_sendmsg+0xcf/0x120 net/socket.c:672
____sys_sendmsg+0x6b9/0x7d0 net/socket.c:2343
___sys_sendmsg+0x100/0x170 net/socket.c:2397
__sys_sendmsg+0xec/0x1b0 net/socket.c:2430
do_syscall_64+0xf6/0x7d0 arch/x86/entry/common.c:294
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x4402e9
Code: 18 89 d0 c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 0f 83 fb 13 fc ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007fffc0fc1f58 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00000000004002c8 RCX: 00000000004402e9
RDX: 0000000000000000 RSI: 0000000020000040 RDI: 0000000000000003
RBP: 00000000006ca018 R08: 0000000000006e61 R09: 00000000004002c8
R10: 0000000000000001 R11: 0000000000000246 R12: 0000000000401b70
R13: 0000000000401c00 R14: 0000000000000000 R15: 0000000000000000
Modules linked in:
---[ end trace 895543aaa6ca5250 ]---
RIP: 0010:erspan_netlink_parms.isra.0+0x5c/0x420 net/ipv4/ip_gre.c:1172
Code: 6a 03 d6 fa 45 85 e4 0f 85 f0 00 00 00 e8 ec 01 d6 fa 48 8d bb b0 00 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 37 03 00 00 4c 8b ab b0 00 00 00 4d 85 ed 0f 84
RSP: 0018:ffffc90001f17080 EFLAGS: 00010202
RAX: dffffc0000000000 RBX: 0000000000000000 RCX: ffffffff869c13c6
RDX: 0000000000000016 RSI: ffffffff869c13d4 RDI: 00000000000000b0
RBP: ffff888090c0a000 R08: ffff88809a4f6240 R09: ffffc90001f170f0
R10: fffff520003e2e24 R11: 0000000000000003 R12: 0000000000000000
R13: ffffc90001f170e0 R14: 0000000000000000 R15: ffffc90001f17428
FS: 0000000001941880(0000) GS:ffff8880ae600000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000020000284 CR3: 000000009e80a000 CR4: 00000000001406f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400


---
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[syzbot]

syzbot has bisected this bug to:

commit e1f8f78ffe9854308b9e12a73ebe4e909074fc33
Author: Petr Machata <pe...@mellanox.com>
Date: Fri Mar 13 11:39:36 2020 +0000

net: ip_gre: Separate ERSPAN newlink / changelink callbacks

bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=101477fde00000
start commit: 0fda7600 geneve: move debug check after netdev unregister
git tree: net
final crash: https://syzkaller.appspot.com/x/report.txt?x=121477fde00000
console output: https://syzkaller.appspot.com/x/log.txt?x=141477fde00000

kernel config: https://syzkaller.appspot.com/x/.config?x=c2e311dba9a02ba9
dashboard link: https://syzkaller.appspot.com/bug?extid=1b4ebf4dae4e510dd219

syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1627f955e00000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=111ac52de00000

Reported-by: syzbot+1b4ebf...@syzkaller.appspotmail.com
Fixes: e1f8f78ffe98 ("net: ip_gre: Separate ERSPAN newlink / changelink callbacks")

For information about bisection process see: https://goo.gl/tpsmEJ#bisection

[Petr Machata]

I've got this reproduced, it happens when IFLA_INFO_DATA is not passed,
so "ip link add type erspan". The problem is that the commit referenced
below doesn't check data != NULL in the ERSPAN branch. I'll send a fix
later today.