Re: [PATCH] ipv6: ensure message length for raw socket is at least sizeof(ipv6hdr)

Alexander Potapenko
2017-04-26T13:00:17Z

On Wed, Apr 26, 2017 at 10:54 AM, Alexander Potapenko <glider@google.com> wrote:
> On Tue, Apr 25, 2017 at 7:55 PM, David Miller <davem@davemloft.net> wrote:
>> From: Alexander Potapenko <glider@google.com>
>> Date: Tue, 25 Apr 2017 15:18:27 +0200
>>
>>> rawv6_send_hdrinc() expects that the buffer copied from the userspace
>>> contains the IPv6 header, so if too few bytes are copied parts of the
>>> header may remain uninitialized.
>>>
>>> This bug has been detected with KMSAN.
>>>
>>> Signed-off-by: Alexander Potapenko <glider@google.com>
>>
>> Hmmm, ipv4 seems to lack this check as well.
>>
>> I think we need to be careful here and fully understand why KMSAN doesn't
>> seem to be triggering in the ipv4 case but for ipv6 it is before I apply
>> this.
> Maybe I just couldn't come up with a decent test case for ipv4 yet.
> syzkaller generated the equivalent of the following program for ipv6:
>
> =======================================
> #define _GNU_SOURCE
>
> #include <netinet/in.h>
> #include <string.h>
> #include <sys/socket.h>
> #include <error.h>
>
> int main()
> {
> int sock = socket(PF_INET6, SOCK_RAW, IPPROTO_RAW);
> struct sockaddr_in6 dest_addr;
> memset(&dest_addr, 0, sizeof(dest_addr));
> dest_addr.sin6_family = AF_INET6;
> inet_pton(AF_INET6, "ff00::", &dest_addr.sin6_addr);
> int err = sendto(sock, 0, 0, 0, &dest_addr, sizeof(dest_addr));
> if (err == -1)
> perror("sendto");
> return 0;
> }
> =======================================
>
> I attempted to replace INET6 and such with INET and provide a legal
> IPv4 address to inet_pton(), but couldn't trigger the warning.
syzkaller reports the following errors in the wild (although there's
no stable repro):

==================================================================
BUG: KMSAN: use of unitialized memory in raw_send_hdrinc
net/ipv4/raw.c:407 [inline]
BUG: KMSAN: use of unitialized memory in raw_sendmsg+0x2c8b/0x3400
net/ipv4/raw.c:640
inter: 0
CPU: 3 PID: 2853 Comm: syz-executor1 Not tainted 4.11.0-rc5+ #2445
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:16 [inline]
dump_stack+0x143/0x1b0 lib/dump_stack.c:52
kmsan_report+0x16b/0x1e0 mm/kmsan/kmsan.c:1078
__kmsan_warning_32+0x5c/0xa0 mm/kmsan/kmsan_instr.c:510
raw_send_hdrinc net/ipv4/raw.c:407 [inline]
raw_sendmsg+0x2c8b/0x3400 net/ipv4/raw.c:640
inet_sendmsg+0x3f8/0x6d0 net/ipv4/af_inet.c:762
sock_sendmsg_nosec net/socket.c:633 [inline]
sock_sendmsg net/socket.c:643 [inline]
___sys_sendmsg+0xd4b/0x10f0 net/socket.c:1997
__sys_sendmsg net/socket.c:2031 [inline]
SYSC_sendmsg+0x2c6/0x3f0 net/socket.c:2042
SyS_sendmsg+0x87/0xb0 net/socket.c:2038
entry_SYSCALL_64_fastpath+0x13/0x94
RIP: 0033:0x44a669
RSP: 002b:00007f08d06edb58 EFLAGS: 00000286 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 0000000000708000 RCX: 000000000044a669
RDX: 0000000000000000 RSI: 0000000020007fc8 RDI: 0000000000000017
RBP: 0000000000005080 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000286 R12: 00000000006e4140
R13: 0000000020b22000 R14: 0000000000000000 R15: 0000000000000000
origin: 00000000cb200085
save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:59
kmsan_save_stack_with_flags mm/kmsan/kmsan.c:362 [inline]
kmsan_internal_poison_shadow+0xb1/0x1a0 mm/kmsan/kmsan.c:257
kmsan_poison_shadow+0x6d/0xc0 mm/kmsan/kmsan.c:270
slab_alloc_node mm/slub.c:2735 [inline]
__kmalloc_node_track_caller+0x1f4/0x390 mm/slub.c:4341
__kmalloc_reserve net/core/skbuff.c:138 [inline]
__alloc_skb+0x2cd/0x740 net/core/skbuff.c:231
alloc_skb include/linux/skbuff.h:933 [inline]
alloc_skb_with_frags+0x209/0xbc0 net/core/skbuff.c:4678
sock_alloc_send_pskb+0x9ff/0xe00 net/core/sock.c:1903
sock_alloc_send_skb+0xe4/0x100 net/core/sock.c:1920
raw_send_hdrinc net/ipv4/raw.c:366 [inline]
raw_sendmsg+0x1db4/0x3400 net/ipv4/raw.c:640
inet_sendmsg+0x3f8/0x6d0 net/ipv4/af_inet.c:762
sock_sendmsg_nosec net/socket.c:633 [inline]
sock_sendmsg net/socket.c:643 [inline]
___sys_sendmsg+0xd4b/0x10f0 net/socket.c:1997
__sys_sendmsg net/socket.c:2031 [inline]
SYSC_sendmsg+0x2c6/0x3f0 net/socket.c:2042
SyS_sendmsg+0x87/0xb0 net/socket.c:2038
entry_SYSCALL_64_fastpath+0x13/0x94
==================================================================

>
>
>
> --
> Alexander Potapenko
> Software Engineer
>
> Google Germany GmbH
> Erika-Mann-Straße, 33
> 80636 München
>
> Geschäftsführer: Matthew Scott Sucherman, Paul Terence Manicle
> Registergericht und -nummer: Hamburg, HRB 86891
> Sitz der Gesellschaft: Hamburg

--
Alexander Potapenko
Software Engineer

Google Germany GmbH
Erika-Mann-Straße, 33
80636 München

Geschäftsführer: Matthew Scott Sucherman, Paul Terence Manicle
Registergericht und -nummer: Hamburg, HRB 86891
Sitz der Gesellschaft: Hamburg