[PATCH net] dccp: avoid deadlock in dccp_v4_ctl_send_reset

[Eric Dumazet]

From: Eric Dumazet <eduma...@google.com>

In the prep work I did before enabling BH while handling socket backlog,
I missed two points in DCCP :

1) dccp_v4_ctl_send_reset() uses bh_lock_sock(), assuming BH were
blocked. It is not anymore always true.

2) dccp_v4_route_skb() was using __IP_INC_STATS() instead of
  IP_INC_STATS()

A similar fix was done for TCP, in commit 47dcc20a39d0
("ipv4: tcp: ip_send_unicast_reply() is not BH safe")

Fixes: 7309f8821fd6 ("dccp: do not assume DCCP code is non preemptible")
Fixes: 5413d1babe8f ("net: do not block BH while processing socket backlog")
Signed-off-by: Eric Dumazet <eduma...@google.com>
Reported-by: Dmitry Vyukov <dvyu...@google.com>
---
 net/dccp/ipv4.c |   10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/net/dccp/ipv4.c b/net/dccp/ipv4.c
index 
5c7e413a3ae407e67565b48a8bd6f43e3b02de4d..25dd25b47d4163625e092c8b96715bb709d85891
 100644
--- a/net/dccp/ipv4.c
+++ b/net/dccp/ipv4.c
@@ -462,7 +462,7 @@ static struct dst_entry* dccp_v4_route_skb(struct net *net, 
struct sock *sk,
        security_skb_classify_flow(skb, flowi4_to_flowi(&fl4));
        rt = ip_route_output_flow(net, &fl4, sk);
        if (IS_ERR(rt)) {
-               __IP_INC_STATS(net, IPSTATS_MIB_OUTNOROUTES);
+               IP_INC_STATS(net, IPSTATS_MIB_OUTNOROUTES);
                return NULL;
        }
 
@@ -527,17 +527,19 @@ static void dccp_v4_ctl_send_reset(const struct sock *sk, 
struct sk_buff *rxskb)
                                                                 rxiph->daddr);
        skb_dst_set(skb, dst_clone(dst));
 
+       local_bh_disable();
        bh_lock_sock(ctl_sk);
        err = ip_build_and_send_pkt(skb, ctl_sk,
                                    rxiph->daddr, rxiph->saddr, NULL);
        bh_unlock_sock(ctl_sk);
 
        if (net_xmit_eval(err) == 0) {
-               DCCP_INC_STATS(DCCP_MIB_OUTSEGS);
-               DCCP_INC_STATS(DCCP_MIB_OUTRSTS);
+               __DCCP_INC_STATS(DCCP_MIB_OUTSEGS);
+               __DCCP_INC_STATS(DCCP_MIB_OUTRSTS);
        }
+       local_bh_enable();
 out:
-        dst_release(dst);
+       dst_release(dst);
 }
 
 static void dccp_v4_reqsk_destructor(struct request_sock *req)