| Message ID | 184e6d2a1ab2e474c12be6e9819d7cf2cc846f26.1518606740.git.pabeni@redhat.com |
|---|---|
| State | Changes Requested |
| Delegated to: | Pablo Neira |
| Headers | show |
| Series | [net,v2] netfilter: nat: cope with negative port range | expand |
On Wed, 2018-02-14 at 12:13 +0100, Paolo Abeni wrote: > syzbot reported a division by 0 bug in the netfilter nat code: ... > 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. I do not quite follow why it is so hard to add a check at parse time. Breaking buggy setups would not be a concern I think. -- To unsubscribe from this list: send the line "unsubscribe netfilter-devel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Eric Dumazet <eric.dumazet@gmail.com> wrote: > On Wed, 2018-02-14 at 12:13 +0100, Paolo Abeni wrote: > > syzbot reported a division by 0 bug in the netfilter nat code: > > > 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. > > I do not quite follow why it is so hard to add a check at parse time. > > Breaking buggy setups would not be a concern I think. It would be possible for xtables but afaics in nft_nat.c case (nft_nat_eval) range.{min,max}_proto.all values are loaded from nft registers at runtime. -- To unsubscribe from this list: send the line "unsubscribe netfilter-devel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Wed, 2018-02-14 at 13:30 +0100, Florian Westphal wrote: > Eric Dumazet <eric.dumazet@gmail.com> wrote: > > On Wed, 2018-02-14 at 12:13 +0100, Paolo Abeni wrote: > > > syzbot reported a division by 0 bug in the netfilter nat code: > > > 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. > > > > I do not quite follow why it is so hard to add a check at parse time. > > > > Breaking buggy setups would not be a concern I think. > > It would be possible for xtables but afaics in nft_nat.c case > (nft_nat_eval) range.{min,max}_proto.all values are loaded from nft > registers at runtime. I prefer this explanation much more, I suggest we update the changelog to explain the real reason. Thanks Florian. -- To unsubscribe from this list: send the line "unsubscribe netfilter-devel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Wed, Feb 14, 2018 at 01:30:37PM +0100, Florian Westphal wrote: > Eric Dumazet <eric.dumazet@gmail.com> wrote: > > On Wed, 2018-02-14 at 12:13 +0100, Paolo Abeni wrote: > > > syzbot reported a division by 0 bug in the netfilter nat code: > > > > > 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. > > > > I do not quite follow why it is so hard to add a check at parse time. > > > > Breaking buggy setups would not be a concern I think. > > It would be possible for xtables but afaics in nft_nat.c case > (nft_nat_eval) range.{min,max}_proto.all values are loaded from nft > registers at runtime. Then, restrict this from nft_nat. -- To unsubscribe from this list: send the line "unsubscribe netfilter-devel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Hi, On Wed, 2018-02-14 at 14:51 +0100, Pablo Neira Ayuso wrote: > On Wed, Feb 14, 2018 at 01:30:37PM +0100, Florian Westphal wrote: > > Eric Dumazet <eric.dumazet@gmail.com> wrote: > > > On Wed, 2018-02-14 at 12:13 +0100, Paolo Abeni wrote: > > > > syzbot reported a division by 0 bug in the netfilter nat code: > > > > 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. > > > > > > I do not quite follow why it is so hard to add a check at parse time. > > > > > > Breaking buggy setups would not be a concern I think. > > > > It would be possible for xtables but afaics in nft_nat.c case > > (nft_nat_eval) range.{min,max}_proto.all values are loaded from nft > > registers at runtime. > > Then, restrict this from nft_nat. If we move the check in the caller for nft, then need cope individually with several control paths (nf_nat_setup_info() is used by ~10 modules if I'm not wrong), I think keeping the check here would be better, do you have strong opinions against that? Thanks, Paolo -- To unsubscribe from this list: send the line "unsubscribe netfilter-devel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Wed, Feb 14, 2018 at 04:45:31PM +0100, Paolo Abeni wrote: > Hi, > > On Wed, 2018-02-14 at 14:51 +0100, Pablo Neira Ayuso wrote: > > On Wed, Feb 14, 2018 at 01:30:37PM +0100, Florian Westphal wrote: > > > Eric Dumazet <eric.dumazet@gmail.com> wrote: > > > > On Wed, 2018-02-14 at 12:13 +0100, Paolo Abeni wrote: > > > > > syzbot reported a division by 0 bug in the netfilter nat code: > > > > > 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. > > > > > > > > I do not quite follow why it is so hard to add a check at parse time. > > > > > > > > Breaking buggy setups would not be a concern I think. > > > > > > It would be possible for xtables but afaics in nft_nat.c case > > > (nft_nat_eval) range.{min,max}_proto.all values are loaded from nft > > > registers at runtime. > > > > Then, restrict this from nft_nat. > > If we move the check in the caller for nft, then need cope individually > with several control paths (nf_nat_setup_info() is used by ~10 modules > if I'm not wrong), I think keeping the check here would be better, do > you have strong opinions against that? You're right, this is fine. Thanks for explaining! -- To unsubscribe from this list: send the line "unsubscribe netfilter-devel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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) {
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 addresses the issue swapping the two ends on negative ranges in nf_nat_l4proto_unique_tuple(). v1 -> v2: use the correct 'Fixes' tag Fixes: 5b1158e909ec ("[NETFILTER]: Add NAT support for nf_conntrack") Reported-and-tested-by: syzbot+8012e198bd037f4871e5@syzkaller.appspotmail.com Signed-off-by: Paolo Abeni <pabeni@redhat.com> --- net/netfilter/nf_nat_proto_common.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-)