[PATCH] net: disable UDP punt on sockets in RCV_SHUTDWON

[PATCH] net: disable UDP punt on sockets in RCV_SHUTDWON

[Chintan Shah]

A UDP application which opens multiple sockets with same local
address/port combination (using SO_REUSEPORT/SO_REUSEADDR socket options);
and issues connect to a remote socket (using one of these local socket).
Now if the same socket, which issued connect, issues shutdown (SHUT_RD);
packets would still be queued to this socket (if sent from same remote
client, which the local socket connected to), and not delivered to the
other socket in the normal state.

In UDP socket lookup, socket's state (if it has issued SHUTDOWN on
read or not), is not taken into account. When application calls, SHUTDOWN
(SHUT_RD), UDP socket's state is changed (sk_shutdown is set to
RCV_SHUTDOWN).

UDP socket lookup is performed with help of compute_score
function. The function checks socket's attributes against incoming packets
headers; and based on match/mismatch it returns score. We can check for
the socket's state (sk->sk_shutdown) here, in same compute_score function,
and return values accordingly.

Signed-off-by: Chintan Shah <chintsha@cisco.com>
CC: xe-linux-external@cisco.com
---
 net/ipv4/udp.c | 6 ++++++
 net/ipv6/udp.c | 6 ++++++
 2 files changed, 12 insertions(+)

diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index 0dfcd73..a5fe6d7 100644
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -402,6 +402,9 @@ static inline int compute_score(struct sock *sk, struct net *net,
 #endif
 #endif
 
+	if (sk->sk_shutdown & RCV_SHUTDOWN)
+		return -1;
+
 	if (!net_eq(sock_net(sk), net) ||
 	    udp_sk(sk)->udp_port_hash != hnum ||
 	    ipv6_only_sock(sk))
@@ -483,6 +486,9 @@ static inline int compute_score2(struct sock *sk, struct net *net,
 #endif
 #endif
 
+	if (sk->sk_shutdown & RCV_SHUTDOWN)
+		return -1;
+
 	if (!net_eq(sock_net(sk), net) ||
 	    ipv6_only_sock(sk))
 		return -1;
diff --git a/net/ipv6/udp.c b/net/ipv6/udp.c
index d956cbb..2254b07 100644
--- a/net/ipv6/udp.c
+++ b/net/ipv6/udp.c
@@ -170,6 +170,9 @@ static inline int compute_score(struct sock *sk, struct net *net,
 #endif
 #endif
 
+	if (sk->sk_shutdown & RCV_SHUTDOWN)
+		return -1;
+
 	if (!net_eq(sock_net(sk), net) ||
 	    udp_sk(sk)->udp_port_hash != hnum ||
 	    sk->sk_family != PF_INET6)
@@ -251,6 +254,9 @@ static inline int compute_score2(struct sock *sk, struct net *net,
 #endif
 #endif
 
+	if (sk->sk_shutdown & RCV_SHUTDOWN)
+		return -1;
+
 	if (!net_eq(sock_net(sk), net) ||
 	    udp_sk(sk)->udp_port_hash != hnum ||
 	    sk->sk_family != PF_INET6)
-- 
2.5.0

Re: [PATCH] net: disable UDP punt on sockets in RCV_SHUTDWON

[Eric Dumazet]

On 05/04/2018 02:08 PM, Chintan Shah wrote:
> A UDP application which opens multiple sockets with same local
> address/port combination (using SO_REUSEPORT/SO_REUSEADDR socket options);
> and issues connect to a remote socket (using one of these local socket).
> Now if the same socket, which issued connect, issues shutdown (SHUT_RD);
> packets would still be queued to this socket (if sent from same remote
> client, which the local socket connected to), and not delivered to the
> other socket in the normal state.
> 

Confusing changelog.

sk_shutdown is on a different cache line, so this additional fetch would cause
loss of performance if many sockets are scanned in the hash bucket.

If you are trying to add full 4-tuple hash table to UDP, and accept() ability,
this would require a bit more than this hack...