Subject: general protection fault in fdb_find_rcu

From: syzbot <[email-masked]>
Date: Sat, 29 Dec 2018 20:01:03 -0800

Hello,

syzbot found the following crash on:

HEAD commit:    90cadbbf341d Merge git://git.kernel.org/pub/scm/linux/kern..
git tree:       net-next
console output: https://syzkaller.appspot.com/x/log.txt?x=1745c69b400000
kernel config:  https://syzkaller.appspot.com/x/.config?x=9d41c8529d7e7362
dashboard link: https://syzkaller.appspot.com/bug?extid=017b1f61c82a1c3e7efd
compiler:       gcc (GCC) 8.0.1 20180413 (experimental)
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=15babaab400000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=14c6142d400000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: [email-masked]

IPv6: ADDRCONF(NETDEV_CHANGE): veth1: link becomes ready
IPv6: ADDRCONF(NETDEV_CHANGE): veth0: link becomes ready
8021q: adding VLAN 0 to HW filter on device team0
kasan: CONFIG_KASAN_INLINE enabled
kasan: GPF could be caused by NULL-ptr deref or user memory access
general protection fault: 0000 [#1] PREEMPT SMP KASAN
CPU: 1 PID: 7824 Comm: syz-executor809 Not tainted 4.20.0-rc7+ #360
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
RIP: 0010:fdb_find_rcu+0x194/0xc90 include/linux/string.h:352
Code: 40 84 c6 0f 85 23 09 00 00 84 c9 0f 95 c2 0f 9e c0 84 c2 0f 85 13 09  
00 00 48 b9 00 00 00 00 00 fc ff df 4c 89 e0 48 c1 e8 03 <0f> b6 14 08 49  
8d 44 24 05 48 89 c6 48 c1 ee 03 0f b6 0c 0e 4c 89
RSP: 0018:ffff8881b932f0b8 EFLAGS: 00010246
RAX: 0000000000000000 RBX: 0000000000000000 RCX: dffffc0000000000
RDX: 0000000000000000 RSI: 1ffff11037265e01 RDI: ffff8881b932f1a8
RBP: ffff8881b932f310 R08: ffff8881bcc84400 R09: ffffed103b5a5b77
R10: ffffed103b5a5b77 R11: ffff8881dad2dbbb R12: 0000000000000000
R13: 0000000000000001 R14: ffff8881b9e68f40 R15: ffff8881b932f2e8
FS:  0000000001e8e880(0000) GS:ffff8881dad00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000020000180 CR3: 00000001bec05000 CR4: 00000000001406e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
  br_fdb_find_rcu net/bridge/br_fdb.c:152 [inline]
  br_fdb_get+0xac/0x230 net/bridge/br_fdb.c:788
  rtnl_fdb_get+0x8a0/0x13b0 net/core/rtnetlink.c:4166
  rtnetlink_rcv_msg+0x46a/0xc20 net/core/rtnetlink.c:5125
  netlink_rcv_skb+0x16c/0x430 net/netlink/af_netlink.c:2477
  rtnetlink_rcv+0x1c/0x20 net/core/rtnetlink.c:5143
  netlink_unicast_kernel net/netlink/af_netlink.c:1310 [inline]
  netlink_unicast+0x59f/0x750 net/netlink/af_netlink.c:1336
  netlink_sendmsg+0xa18/0xfc0 net/netlink/af_netlink.c:1917
  sock_sendmsg_nosec net/socket.c:621 [inline]
  sock_sendmsg+0xd5/0x120 net/socket.c:631
  ___sys_sendmsg+0x7fd/0x930 net/socket.c:2116
  __sys_sendmsg+0x11d/0x280 net/socket.c:2154
  __do_sys_sendmsg net/socket.c:2163 [inline]
  __se_sys_sendmsg net/socket.c:2161 [inline]
  __x64_sys_sendmsg+0x78/0xb0 net/socket.c:2161
  do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
  entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x441679
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 2b 09 fc ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007fff99382768 EFLAGS: 00000213 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 0000000000441679
RDX: 0000000000000000 RSI: 0000000020000180 RDI: 0000000000000003
RBP: 00000000006cd018 R08: 0000000000000100 R09: 0000000000000100
R10: 0000000000000020 R11: 0000000000000213 R12: 0000000000402430
R13: 00000000004024c0 R14: 0000000000000000 R15: 0000000000000000
Modules linked in:
---[ end trace d6d5286333ca98b5 ]---
RIP: 0010:fdb_find_rcu+0x194/0xc90 include/linux/string.h:352
Code: 40 84 c6 0f 85 23 09 00 00 84 c9 0f 95 c2 0f 9e c0 84 c2 0f 85 13 09  
00 00 48 b9 00 00 00 00 00 fc ff df 4c 89 e0 48 c1 e8 03 <0f> b6 14 08 49  
8d 44 24 05 48 89 c6 48 c1 ee 03 0f b6 0c 0e 4c 89
RSP: 0018:ffff8881b932f0b8 EFLAGS: 00010246
RAX: 0000000000000000 RBX: 0000000000000000 RCX: dffffc0000000000
RDX: 0000000000000000 RSI: 1ffff11037265e01 RDI: ffff8881b932f1a8
RBP: ffff8881b932f310 R08: ffff8881bcc84400 R09: ffffed103b5a5b77
R10: ffffed103b5a5b77 R11: ffff8881dad2dbbb R12: 0000000000000000
R13: 0000000000000001 R14: ffff8881b9e68f40 R15: ffff8881b932f2e8
FS:  0000000001e8e880(0000) GS:ffff8881dad00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000020000180 CR3: 00000001bec05000 CR4: 00000000001406e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400

---
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