net: GPF in rt6_get_cookie

[Dmitry Vyukov]

Hello,

I got several GPFs in rt6_get_cookie while running syzkaller:

general protection fault: 0000 [#1] SMP DEBUG_PAGEALLOC KASAN
Dumping ftrace buffer:
   (ftrace buffer empty)
Modules linked in:
CPU: 2 PID: 10156 Comm: syz-executor Not tainted 4.9.0-rc5+ #54
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
task: ffff880016f40480 task.stack: ffff88000fc00000
RIP: 0010:[<ffffffff87a209e8>]  [<     inline     >] rt6_get_cookie
include/net/ip6_fib.h:174
RIP: 0010:[<ffffffff87a209e8>]  [<ffffffff87a209e8>]
sctp_v6_get_dst+0x7c8/0x1960 net/sctp/ipv6.c:340
RSP: 0018:ffff88000fc07298  EFLAGS: 00010202
RAX: dffffc0000000000 RBX: 0000000000000000 RCX: ffffc900029f5000
RDX: 0000000000000015 RSI: 0000000000000001 RDI: 00000000000000a8
RBP: ffff88000fc07580 R08: 0000000000000000 R09: 0000000000000001
R10: 0000000000000000 R11: 0000000000000000 R12: ffff880066cd0068
R13: 1ffff10001f80e92 R14: ffff880066cd0040 R15: ffff88005f2d2808
FS:  00007f52c41f7700(0000) GS:ffff88006d000000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000020016000 CR3: 0000000065dd7000 CR4: 00000000000006e0
DR0: 0000000000000400 DR1: 0000000000000400 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000600
Stack:
 ffffffff87a210f6 ffffffff8701ad45 ffff88006768ec20 ffff88006768ec20
 0000000000000000 0000000016f40480 ffff88000fc07450 1ffff1000cd9a017
 ffff88006768ec00 ffff880066fc0730 ffff880066cd0068 1ffff10001f80e66
Call Trace:
 [<ffffffff879a313d>] sctp_transport_route+0xad/0x430 net/sctp/transport.c:279
 [<ffffffff8799b106>] sctp_assoc_add_peer+0x5a6/0x13e0 net/sctp/associola.c:641
 [<ffffffff879e8911>] sctp_sendmsg+0x1921/0x3bc0 net/sctp/socket.c:1864
 [<ffffffff8701ad45>] inet_sendmsg+0x385/0x590 net/ipv4/af_inet.c:734
 [<     inline     >] sock_sendmsg_nosec net/socket.c:621
 [<ffffffff86a6d54f>] sock_sendmsg+0xcf/0x110 net/socket.c:631
 [<ffffffff86a6ede0>] SYSC_sendto+0x660/0x810 net/socket.c:1656
 [<ffffffff86a71dd5>] SyS_sendto+0x45/0x60 net/socket.c:1624
 [<ffffffff88149dc5>] entry_SYSCALL_64_fastpath+0x23/0xc6
Code: 00 00 48 8b 84 24 88 00 00 00 48 8b 58 40 e8 80 76 cc f9 48 8d
bb a8 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 56 0f 00 00 48 8b 9b a8 00 00 00 45 31 ed 48
RIP  [<     inline     >] rt6_get_cookie include/net/ip6_fib.h:174
RIP  [<ffffffff87a209e8>] sctp_v6_get_dst+0x7c8/0x1960 net/sctp/ipv6.c:340
 RSP <ffff88000fc07298>
---[ end trace b8d1354fa571700d ]---


general protection fault: 0000 [#1] SMP DEBUG_PAGEALLOC KASAN
Dumping ftrace buffer:
   (ftrace buffer empty)
Modules linked in:
CPU: 3 PID: 22744 Comm: syz-executor Not tainted 4.9.0-rc5+ #54
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
task: ffff88006b92a840 task.stack: ffff88006a730000
RIP: 0010:[<ffffffff87a209e8>]  [<     inline     >] rt6_get_cookie
include/net/ip6_fib.h:174
RIP: 0010:[<ffffffff87a209e8>]  [<ffffffff87a209e8>]
sctp_v6_get_dst+0x7c8/0x1960 net/sctp/ipv6.c:340
RSP: 0018:ffff88006a736b88  EFLAGS: 00010202
RAX: dffffc0000000000 RBX: 0000000000000000 RCX: ffffc90003c4f000
RDX: 0000000000000015 RSI: 0000000000000001 RDI: 00000000000000a8
RBP: ffff88006a736e68 R08: 0000000000000000 R09: 0000000000000001
R10: 0000000000000000 R11: 0000000000000000 R12: ffff880064cff268
R13: 1ffff1000d4e6db0 R14: ffff880064cff240 R15: ffff88006a4b6808
FS:  00007f74f4ec9700(0000) GS:ffff88006d100000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000000002070effc CR3: 000000003bd2f000 CR4: 00000000000006e0
DR0: 0000000000000400 DR1: 0000000000000400 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000600
Stack:
 ffffffff87a210f6 ffffffff000bbd2d ffff88006c2cd5a0 ffff88006c2cd5a0
 0000000000000000 000000006ccb46c0 ffff88006a736d40 1ffff1000c99fe57
 ffff88006c2cd500 ffff8800658b1f30 ffff880064cff268 1ffff1000d4e6d84
Call Trace:
 [<ffffffff879a313d>] sctp_transport_route+0xad/0x430 net/sctp/transport.c:279
 [<ffffffff8799b106>] sctp_assoc_add_peer+0x5a6/0x13e0 net/sctp/associola.c:641
 [<ffffffff879e4358>] __sctp_connect+0x288/0xc90 net/sctp/socket.c:1178
 [<ffffffff879e4f0b>] __sctp_setsockopt_connectx+0x1ab/0x200
net/sctp/socket.c:1332
 [<     inline     >] sctp_getsockopt_connectx3 net/sctp/socket.c:1417
 [<ffffffff879fd2bd>] sctp_getsockopt+0x36ed/0x6800 net/sctp/socket.c:6474
 [<ffffffff86a76c0a>] sock_common_getsockopt+0x9a/0xe0 net/core/sock.c:2649
 [<     inline     >] SYSC_getsockopt net/socket.c:1788
 [<ffffffff86a724d7>] SyS_getsockopt+0x257/0x390 net/socket.c:1770
 [<ffffffff88149dc5>] entry_SYSCALL_64_fastpath+0x23/0xc6
Code: 00 00 48 8b 84 24 88 00 00 00 48 8b 58 40 e8 80 76 cc f9 48 8d
bb a8 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 56 0f 00 00 48 8b 9b a8 00 00 00 45 31 ed 48
RIP  [<     inline     >] rt6_get_cookie include/net/ip6_fib.h:174
RIP  [<ffffffff87a209e8>] sctp_v6_get_dst+0x7c8/0x1960 net/sctp/ipv6.c:340
 RSP <ffff88006a736b88>
---[ end trace f42d1c14cb6d2835 ]---

This happened on commit a25f0944ba9b1d8a6813fd6f1a86f1bd59ac25a6 (Nov 13).

Unfortunately this is not reproducible.

The line is:

    return rt->rt6i_node ? rt->rt6i_node->fn_sernum : 0;

Can it be a data race? rt->rt6i_node != NULL, but the next moment it
is already NULL? That would explain the crash and non-reproducibility
(need ThreadSanitizer!).

This always happened when called from sctp code, but I don't know if
it is relevant or not. It happened only 3 times.

Thanks.