commit 286c72deabaa240b7eebbd99496ed3324d69f3c0
author Eric Dumazet <edumazet@google.com> Thu Oct 20 09:39:40 2016 -0700
committer David S. Miller <davem@davemloft.net> Thu Oct 20 14:45:52 2016 -0400
tree 00a0b07bfc20b08a025720c4c1b3c724ed4eaf67
parent 2399d6143f85b155ae84ccd94237befd36b8f6c7

udp: must lock the socket in udp_disconnect()

Baozeng Ding reported KASAN traces showing uses after free in
udp_lib_get_port() and other related UDP functions.

A CONFIG_DEBUG_PAGEALLOC=y kernel would eventually crash.

I could write a reproducer with two threads doing :

static int sock_fd;
static void *thr1(void *arg)
{
	for (;;) {
		connect(sock_fd, (const struct sockaddr *)arg,
			sizeof(struct sockaddr_in));
	}
}

static void *thr2(void *arg)
{
	struct sockaddr_in unspec;

	for (;;) {
		memset(&unspec, 0, sizeof(unspec));
	        connect(sock_fd, (const struct sockaddr *)&unspec,
			sizeof(unspec));
        }
}

Problem is that udp_disconnect() could run without holding socket lock,
and this was causing list corruptions.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: Baozeng Ding <sploving1@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/ping.c

diff --git a/net/ipv4/ping.c b/net/ipv4/ping.c
index 7cf7d6e..205e200 100644
--- a/net/ipv4/ping.c
+++ b/net/ipv4/ping.c
@@ -994,7 +994,7 @@ struct proto ping_prot = {
 	.init =		ping_init_sock,
 	.close =	ping_close,
 	.connect =	ip4_datagram_connect,
-	.disconnect =	udp_disconnect,
+	.disconnect =	__udp_disconnect,
 	.setsockopt =	ip_setsockopt,
 	.getsockopt =	ip_getsockopt,
 	.sendmsg =	ping_v4_sendmsg,

net/ipv4/raw.c

diff --git a/net/ipv4/raw.c b/net/ipv4/raw.c
index 90a85c9..ecbe5a7 100644
--- a/net/ipv4/raw.c
+++ b/net/ipv4/raw.c
@@ -918,7 +918,7 @@ struct proto raw_prot = {
 	.close		   = raw_close,
 	.destroy	   = raw_destroy,
 	.connect	   = ip4_datagram_connect,
-	.disconnect	   = udp_disconnect,
+	.disconnect	   = __udp_disconnect,
 	.ioctl		   = raw_ioctl,
 	.init		   = raw_init,
 	.setsockopt	   = raw_setsockopt,

net/ipv4/udp.c

diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index 7d96dc2..311613e 100644
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -1345,7 +1345,7 @@ int udp_recvmsg(struct sock *sk, struct msghdr *msg, size_t len, int noblock,
 	goto try_again;
 }
 
-int udp_disconnect(struct sock *sk, int flags)
+int __udp_disconnect(struct sock *sk, int flags)
 {
 	struct inet_sock *inet = inet_sk(sk);
 	/*
@@ -1367,6 +1367,15 @@ int udp_disconnect(struct sock *sk, int flags)
 	sk_dst_reset(sk);
 	return 0;
 }
+EXPORT_SYMBOL(__udp_disconnect);
+
+int udp_disconnect(struct sock *sk, int flags)
+{
+	lock_sock(sk);
+	__udp_disconnect(sk, flags);
+	release_sock(sk);
+	return 0;
+}
 EXPORT_SYMBOL(udp_disconnect);
 
 void udp_lib_unhash(struct sock *sk)
@@ -2193,7 +2202,7 @@ int udp_abort(struct sock *sk, int err)
 
 	sk->sk_err = err;
 	sk->sk_error_report(sk);
-	udp_disconnect(sk, 0);
+	__udp_disconnect(sk, 0);
 
 	release_sock(sk);