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, 1 insertions, 3 deletions

diff --git a/net/ipv4/raw.c b/net/ipv4/raw.c
index 41e1d2845c8f..5cb8ddb505ee 100644
--- a/net/ipv4/raw.c
+++ b/net/ipv4/raw.c
@@ -696,9 +696,6 @@ static int raw_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) {
                 err = ip_recv_error(sk, msg, len);
                 goto out;
@@ -726,6 +723,7 @@ static int raw_recvmsg(struct kiocb *iocb, struct sock *sk, struct msghdr *msg,
                 sin->sin_addr.s_addr = ip_hdr(skb)->saddr;
                 sin->sin_port = 0;
                 memset(&sin->sin_zero, 0, sizeof(sin->sin_zero));
+                *addr_len = sizeof(*sin);
         }
         if (inet->cmsg_flags)
                 ip_cmsg_recv(msg, skb);