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

[ Upstream commit bceaa90240b6019ed73b49965eac7d167610be69 ]

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 4 insertions, 5 deletions

diff --git a/net/ipv4/ping.c b/net/ipv4/ping.c
index 7d93d62cd5fd..be01d5b8571a 100644
--- a/net/ipv4/ping.c
+++ b/net/ipv4/ping.c
@@ -626,7 +626,6 @@ static int ping_recvmsg(struct kiocb *iocb, struct sock *sk, struct msghdr *msg,
                         size_t len, int noblock, int flags, int *addr_len)
 {
         struct inet_sock *isk = inet_sk(sk);
-        struct sockaddr_in *sin = (struct sockaddr_in *)msg->msg_name;
         struct sk_buff *skb;
         int copied, err;
 
@@ -636,9 +635,6 @@ static int ping_recvmsg(struct kiocb *iocb, struct sock *sk, struct msghdr *msg,
         if (flags & MSG_OOB)
                 goto out;
 
-        if (addr_len)
-                *addr_len = sizeof(*sin);
-
         if (flags & MSG_ERRQUEUE)
                 return ip_recv_error(sk, msg, len);
 
@@ -660,11 +656,14 @@ static int ping_recvmsg(struct kiocb *iocb, struct sock *sk, struct msghdr *msg,
         sock_recv_timestamp(msg, sk, skb);
 
         /* Copy the address. */
-        if (sin) {
+        if (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);