From: Chieh-Min Wang <chiehm...@synology.com>
For bridge or multicast packets, they could cloned skb with unconfirmed
conntrack
which break the rule unconfirmed skb->nfct is never shared. With nfqueue
running
on my system, the race can be easily reproduced with following warning
calltrace:
[13257.707525] CPU: 0 PID: 12132 Comm: main Tainted: P W 4.4.60
#7744
[13257.707568] Hardware name: Qualcomm (Flattened Device Tree)
[13257.714700] [<c021f6dc>] (unwind_backtrace) from [<c021bce8>]
(show_stack+0x10/0x14)
[13257.720253] [<c021bce8>] (show_stack) from [<c0449e10>]
(dump_stack+0x94/0xa8)
[13257.728240] [<c0449e10>] (dump_stack) from [<c022a7e0>]
(warn_slowpath_common+0x94/0xb0)
[13257.735268] [<c022a7e0>] (warn_slowpath_common) from [<c022a898>]
(warn_slowpath_null+0x1c/0x24)
[13257.743519] [<c022a898>] (warn_slowpath_null) from [<c06ee450>]
(__nf_conntrack_confirm+0xa8/0x618)
[13257.752284] [<c06ee450>] (__nf_conntrack_confirm) from [<c0772670>]
(ipv4_confirm+0xb8/0xfc)
[13257.761049] [<c0772670>] (ipv4_confirm) from [<c06e7a60>]
(nf_iterate+0x48/0xa8)
[13257.769725] [<c06e7a60>] (nf_iterate) from [<c06e7af0>]
(nf_hook_slow+0x30/0xb0)
[13257.777108] [<c06e7af0>] (nf_hook_slow) from [<c07f20b4>]
(br_nf_post_routing+0x274/0x31c)
[13257.784486] [<c07f20b4>] (br_nf_post_routing) from [<c06e7a60>]
(nf_iterate+0x48/0xa8)
[13257.792556] [<c06e7a60>] (nf_iterate) from [<c06e7af0>]
(nf_hook_slow+0x30/0xb0)
[13257.800458] [<c06e7af0>] (nf_hook_slow) from [<c07e5580>]
(br_forward_finish+0x94/0xa4)
[13257.808010] [<c07e5580>] (br_forward_finish) from [<c07f22ac>]
(br_nf_forward_finish+0x150/0x1ac)
[13257.815736] [<c07f22ac>] (br_nf_forward_finish) from [<c06e8df0>]
(nf_reinject+0x108/0x170)
[13257.824762] [<c06e8df0>] (nf_reinject) from [<c06ea854>]
(nfqnl_recv_verdict+0x3d8/0x420)
[13257.832924] [<c06ea854>] (nfqnl_recv_verdict) from [<c06e940c>]
(nfnetlink_rcv_msg+0x158/0x248)
[13257.841256] [<c06e940c>] (nfnetlink_rcv_msg) from [<c06e5564>]
(netlink_rcv_skb+0x54/0xb0)
[13257.849762] [<c06e5564>] (netlink_rcv_skb) from [<c06e4ec8>]
(netlink_unicast+0x148/0x23c)
[13257.858093] [<c06e4ec8>] (netlink_unicast) from [<c06e5364>]
(netlink_sendmsg+0x2ec/0x368)
[13257.866348] [<c06e5364>] (netlink_sendmsg) from [<c069fb8c>]
(sock_sendmsg+0x34/0x44)
[13257.874590] [<c069fb8c>] (sock_sendmsg) from [<c06a03dc>]
(___sys_sendmsg+0x1ec/0x200)
[13257.882489] [<c06a03dc>] (___sys_sendmsg) from [<c06a11c8>]
(__sys_sendmsg+0x3c/0x64)
[13257.890300] [<c06a11c8>] (__sys_sendmsg) from [<c0209b40>]
(ret_fast_syscall+0x0/0x34)
The original code just triggered the warning but do nothing. It will caused the
shared
conntrack moves to the dying list and the packet be droppped
(nf_ct_resolve_clash returns
NF_DROP for dying conntrack).
---
net/netfilter/nf_conntrack_core.c | 12 +++++++++---
1 file changed, 9 insertions(+), 3 deletions(-)
diff --git a/net/netfilter/nf_conntrack_core.c
b/net/netfilter/nf_conntrack_core.c
index ca1168d..94e6c85 100644
--- a/net/netfilter/nf_conntrack_core.c
+++ b/net/netfilter/nf_conntrack_core.c
@@ -901,10 +901,16 @@ __nf_conntrack_confirm(struct sk_buff *skb)
* REJECT will give spurious warnings here.
*/
- /* No external references means no one else could have
- * confirmed us.
+ /* Another skb with the same unconfirmed conntrack may
+ * win the race. This may happen for bridge or multicast
+ * packets that skb_clone skb with unconfirmed conntrack.
*/
- WARN_ON(nf_ct_is_confirmed(ct));
+ if (nf_ct_is_confirmed(ct)) {
+ nf_conntrack_double_unlock(hash, reply_hash);
+ local_bh_enable();
+ return NF_ACCEPT;
+ }
+
pr_debug("Confirming conntrack %p\n", ct);
/* We have to check the DYING flag after unlink to prevent
* a race against nf_ct_get_next_corpse() possibly called from
--
2.7.4
