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

Alexander Potapenko
2017-04-25T13:18:27Z

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>
---
For the record, the KMSAN report:

==================================================================
BUG: KMSAN: use of unitialized memory in nf_ct_frag6_gather+0xf5a/0x44a0
inter: 0
CPU: 0 PID: 1036 Comm: probe Not tainted 4.11.0-rc5+ #2455
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:16
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
nf_ct_frag6_gather+0xf5a/0x44a0 net/ipv6/netfilter/nf_conntrack_reasm.c:577
ipv6_defrag+0x1d9/0x280 net/ipv6/netfilter/nf_defrag_ipv6_hooks.c:68
nf_hook_entry_hookfn ./include/linux/netfilter.h:102
nf_hook_slow+0x13f/0x3c0 net/netfilter/core.c:310
nf_hook ./include/linux/netfilter.h:212
NF_HOOK ./include/linux/netfilter.h:255
rawv6_send_hdrinc net/ipv6/raw.c:673
rawv6_sendmsg+0x2fcb/0x41a0 net/ipv6/raw.c:919
inet_sendmsg+0x3f8/0x6d0 net/ipv4/af_inet.c:762
sock_sendmsg_nosec net/socket.c:633
sock_sendmsg net/socket.c:643
SYSC_sendto+0x6a5/0x7c0 net/socket.c:1696
SyS_sendto+0xbc/0xe0 net/socket.c:1664
do_syscall_64+0x72/0xa0 arch/x86/entry/common.c:285
entry_SYSCALL64_slow_path+0x25/0x25 arch/x86/entry/entry_64.S:246
RIP: 0033:0x436e03
RSP: 002b:00007ffce48baf38 EFLAGS: 00000246 ORIG_RAX: 000000000000002c
RAX: ffffffffffffffda RBX: 00000000004002b0 RCX: 0000000000436e03
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000003
RBP: 00007ffce48baf90 R08: 00007ffce48baf50 R09: 000000000000001c
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000401790 R14: 0000000000401820 R15: 0000000000000000
origin: 00000000d9400053
save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:59
kmsan_save_stack_with_flags mm/kmsan/kmsan.c:362
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
__kmalloc_node_track_caller+0x1f4/0x390 mm/slub.c:4341
__kmalloc_reserve net/core/skbuff.c:138
__alloc_skb+0x2cd/0x740 net/core/skbuff.c:231
alloc_skb ./include/linux/skbuff.h:933
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
rawv6_send_hdrinc net/ipv6/raw.c:638
rawv6_sendmsg+0x2918/0x41a0 net/ipv6/raw.c:919
inet_sendmsg+0x3f8/0x6d0 net/ipv4/af_inet.c:762
sock_sendmsg_nosec net/socket.c:633
sock_sendmsg net/socket.c:643
SYSC_sendto+0x6a5/0x7c0 net/socket.c:1696
SyS_sendto+0xbc/0xe0 net/socket.c:1664
do_syscall_64+0x72/0xa0 arch/x86/entry/common.c:285
return_from_SYSCALL_64+0x0/0x6a arch/x86/entry/entry_64.S:246
==================================================================

, triggered by the following syscalls:
socket(PF_INET6, SOCK_RAW, IPPROTO_RAW) = 3
sendto(3, NULL, 0, 0, {sa_family=AF_INET6, sin6_port=htons(0), inet_pton(AF_INET6, "ff00::", &sin6_addr), sin6_flowinfo=0, sin6_scope_id=0}, 28) = -1 EPERM
---
net/ipv6/raw.c | 2 ++
1 file changed, 2 insertions(+)

diff --git a/net/ipv6/raw.c b/net/ipv6/raw.c
index f174e76e6505..805464668bd8 100644
--- a/net/ipv6/raw.c
+++ b/net/ipv6/raw.c
@@ -632,6 +632,8 @@ static int rawv6_send_hdrinc(struct sock *sk, struct msghdr *msg, int length,
ipv6_local_error(sk, EMSGSIZE, fl6, rt->dst.dev->mtu);
return -EMSGSIZE;
}
+ if (length < sizeof(struct ipv6hdr))
+ return -EINVAL;
if (flags&MSG_PROBE)
goto out;

--
2.13.0.rc0.306.g87b477812d-goog