syzbot reported a division by 0 bug in the netfilter nat code:
divide error: 0000 [#1] SMP KASAN
Dumping ftrace buffer:
(ftrace buffer empty)
Modules linked in:
CPU: 1 PID: 4168 Comm: syzkaller034710 Not tainted 4.16.0-rc1+ #309
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
RIP: 0010:nf_nat_l4proto_unique_tuple+0x291/0x530
net/netfilter/nf_nat_proto_common.c:88
RSP: 0018:ffff8801b2466778 EFLAGS: 00010246
RAX: 000000000000f153 RBX: ffff8801b2466dd8 RCX: ffff8801b2466c7c
RDX: 0000000000000000 RSI: ffff8801b2466c58 RDI: ffff8801db5293ac
RBP: ffff8801b24667d8 R08: ffff8801b8ba6dc0 R09: ffffffff88af5900
R10: ffff8801b24666f0 R11: 0000000000000000 R12: 000000002990f153
R13: 0000000000000001 R14: 0000000000000000 R15: ffff8801b2466c7c
FS: 00000000017e3880(0000) GS:ffff8801db500000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00000000208fdfe4 CR3: 00000001b5340002 CR4: 00000000001606e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
dccp_unique_tuple+0x40/0x50 net/netfilter/nf_nat_proto_dccp.c:30
get_unique_tuple+0xc28/0x1c10 net/netfilter/nf_nat_core.c:362
nf_nat_setup_info+0x1c2/0xe00 net/netfilter/nf_nat_core.c:406
nf_nat_redirect_ipv6+0x306/0x730 net/netfilter/nf_nat_redirect.c:124
redirect_tg6+0x7f/0xb0 net/netfilter/xt_REDIRECT.c:34
ip6t_do_table+0xc2a/0x1a30 net/ipv6/netfilter/ip6_tables.c:365
ip6table_nat_do_chain+0x65/0x80 net/ipv6/netfilter/ip6table_nat.c:41
nf_nat_ipv6_fn+0x594/0xa80 net/ipv6/netfilter/nf_nat_l3proto_ipv6.c:302
nf_nat_ipv6_local_fn+0x33/0x5d0
net/ipv6/netfilter/nf_nat_l3proto_ipv6.c:407
ip6table_nat_local_fn+0x2c/0x40 net/ipv6/netfilter/ip6table_nat.c:69
nf_hook_entry_hookfn include/linux/netfilter.h:120 [inline]
nf_hook_slow+0xba/0x1a0 net/netfilter/core.c:483
nf_hook include/linux/netfilter.h:243 [inline]
NF_HOOK include/linux/netfilter.h:286 [inline]
ip6_xmit+0x10ec/0x2260 net/ipv6/ip6_output.c:277
inet6_csk_xmit+0x2fc/0x580 net/ipv6/inet6_connection_sock.c:139
dccp_transmit_skb+0x9ac/0x10f0 net/dccp/output.c:142
dccp_connect+0x369/0x670 net/dccp/output.c:564
dccp_v6_connect+0xe17/0x1bf0 net/dccp/ipv6.c:946
__inet_stream_connect+0x2d4/0xf00 net/ipv4/af_inet.c:620
inet_stream_connect+0x58/0xa0 net/ipv4/af_inet.c:684
SYSC_connect+0x213/0x4a0 net/socket.c:1639
SyS_connect+0x24/0x30 net/socket.c:1620
do_syscall_64+0x282/0x940 arch/x86/entry/common.c:287
entry_SYSCALL_64_after_hwframe+0x26/0x9b
RIP: 0033:0x441c69
RSP: 002b:00007ffe50cc0be8 EFLAGS: 00000217 ORIG_RAX: 000000000000002a
RAX: ffffffffffffffda RBX: ffffffffffffffff RCX: 0000000000441c69
RDX: 000000000000001c RSI: 00000000208fdfe4 RDI: 0000000000000003
RBP: 00000000006cc018 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000538 R11: 0000000000000217 R12: 0000000000403590
R13: 0000000000403620 R14: 0000000000000000 R15: 0000000000000000
Code: 48 89 f0 83 e0 07 83 c0 01 38 d0 7c 08 84 d2 0f 85 46 02 00 00 48 8b
45 c8 44 0f b7 20 e8 88 97 04 fd 31 d2 41 0f b7 c4 4c 89 f9 <41> f7 f6 48
c1 e9 03 48 b8 00 00 00 00 00 fc ff df 0f b6 0c 01
RIP: nf_nat_l4proto_unique_tuple+0x291/0x530
net/netfilter/nf_nat_proto_common.c:88 RSP: ffff8801b2466778
The problem is that currently we don't have any check on the
configured port range. A port range == -1 triggers the bug, while
other negative values may require a very long time to complete the
following loop.
Adding the relevant check at parse time could break existing
setup, moreover we would need to read/write such values atomically
to avoid possible transient negative ranges at update time.
This commit address the issue swapping the two ends on negative
ranges in nf_nat_l4proto_unique_tuple().
Fixes: c7232c9979cb ("netfilter: add protocol independent NAT core")
Reported-and-tested-by: syzbot+8012e198bd037f4871e5@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Paolo Abeni <pabeni@xxxxxxxxxx>
---
net/netfilter/nf_nat_proto_common.c | 9 ++++++---
1 file changed, 6 insertions(+), 3 deletions(-)
diff --git a/net/netfilter/nf_nat_proto_common.c b/net/netfilter/nf_nat_proto_common.c
index fbce552a796e..a05cce545e98 100644
--- a/net/netfilter/nf_nat_proto_common.c
+++ b/net/netfilter/nf_nat_proto_common.c
@@ -41,7 +41,7 @@ void nf_nat_l4proto_unique_tuple(const struct nf_nat_l3proto *l3proto,
const struct nf_conn *ct,
u16 *rover)
{
- unsigned int range_size, min, i;
+ unsigned int range_size, min, max, i;
__be16 *portptr;
u_int16_t off;
@@ -70,8 +70,11 @@ void nf_nat_l4proto_unique_tuple(const struct nf_nat_l3proto *l3proto,
range_size = 65535 - 1024 + 1;
}
} else {
- min = ntohs(range->min_proto.all);
- range_size = ntohs(range->max_proto.all) - min + 1;
+ min = ntohs(READ_ONCE(range->min_proto.all));
+ max = ntohs(READ_ONCE(range->max_proto.all));
+ if (unlikely(max < min))
+ swap(min, max);
+ range_size = max - min + 1;
}
if (range->flags & NF_NAT_RANGE_PROTO_RANDOM) {
--
2.14.3
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