inet: prevent leakage of uninitialized memory to user in recv syscalls

Only update *addr_len when we actually fill in sockaddr, otherwise we
can return uninitialized memory from the stack to the caller in the
recvfrom, recvmmsg and recvmsg syscalls. Drop the the (addr_len == NULL)
checks because we only get called with a valid addr_len pointer either
from sock_common_recvmsg or inet_recvmsg.

If a blocking read waits on a socket which is concurrently shut down we
now return zero and set msg_msgnamelen to 0.

Reported-by: mpb <mpb.mail@gmail.com>
Suggested-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 7 insertions, 12 deletions

diff --git a/net/ipv4/ping.c b/net/ipv4/ping.c
index 9afbdb1..aacefa0 100644
--- a/net/ipv4/ping.c
+++ b/net/ipv4/ping.c
@@ -830,8 +830,6 @@ int ping_recvmsg(struct kiocb *iocb, struct sock *sk, struct msghdr *msg,
 {
 	struct inet_sock *isk = inet_sk(sk);
 	int family = sk->sk_family;
-	struct sockaddr_in *sin;
-	struct sockaddr_in6 *sin6;
 	struct sk_buff *skb;
 	int copied, err;
 
@@ -841,13 +839,6 @@ int ping_recvmsg(struct kiocb *iocb, struct sock *sk, struct msghdr *msg,
 	if (flags & MSG_OOB)
 		goto out;
 
-	if (addr_len) {
-		if (family == AF_INET)
-			*addr_len = sizeof(*sin);
-		else if (family == AF_INET6 && addr_len)
-			*addr_len = sizeof(*sin6);
-	}
-
 	if (flags & MSG_ERRQUEUE) {
 		if (family == AF_INET) {
 			return ip_recv_error(sk, msg, len);
@@ -877,11 +868,13 @@ int ping_recvmsg(struct kiocb *iocb, struct sock *sk, struct msghdr *msg,
 
 	/* Copy the address and add cmsg data. */
 	if (family == AF_INET) {
-		sin = (struct sockaddr_in *) msg->msg_name;
+		struct sockaddr_in *sin = (struct sockaddr_in *)msg->msg_name;
+
 		sin->sin_family = AF_INET;
 		sin->sin_port = 0 /* skb->h.uh->source */;
 		sin->sin_addr.s_addr = ip_hdr(skb)->saddr;
 		memset(sin->sin_zero, 0, sizeof(sin->sin_zero));
+		*addr_len = sizeof(*sin);
 
 		if (isk->cmsg_flags)
 			ip_cmsg_recv(msg, skb);
@@ -890,17 +883,19 @@ int ping_recvmsg(struct kiocb *iocb, struct sock *sk, struct msghdr *msg,
 	} else if (family == AF_INET6) {
 		struct ipv6_pinfo *np = inet6_sk(sk);
 		struct ipv6hdr *ip6 = ipv6_hdr(skb);
-		sin6 = (struct sockaddr_in6 *) msg->msg_name;
+		struct sockaddr_in6 *sin6 =
+			(struct sockaddr_in6 *)msg->msg_name;
+
 		sin6->sin6_family = AF_INET6;
 		sin6->sin6_port = 0;
 		sin6->sin6_addr = ip6->saddr;
-
 		sin6->sin6_flowinfo = 0;
 		if (np->sndflow)
 			sin6->sin6_flowinfo = ip6_flowinfo(ip6);
 
 		sin6->sin6_scope_id = ipv6_iface_scope_id(&sin6->sin6_addr,
 							  IP6CB(skb)->iif);
+		*addr_len = sizeof(*sin6);
 
 		if (inet6_sk(sk)->rxopt.all)
 			pingv6_ops.ip6_datagram_recv_ctl(sk, msg, skb);