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>

2 files changed, 2 insertions, 7 deletions

diff --git a/net/ipv6/raw.c b/net/ipv6/raw.c
index 3c00842b0079..e24ff1df0401 100644
--- a/net/ipv6/raw.c
+++ b/net/ipv6/raw.c
@@ -465,9 +465,6 @@ static int rawv6_recvmsg(struct kiocb *iocb, struct sock *sk,
         if (flags & MSG_OOB)
                 return -EOPNOTSUPP;
 
-        if (addr_len)
-                *addr_len=sizeof(*sin6);
-
         if (flags & MSG_ERRQUEUE)
                 return ipv6_recv_error(sk, msg, len);
 
@@ -506,6 +503,7 @@ static int rawv6_recvmsg(struct kiocb *iocb, struct sock *sk,
                 sin6->sin6_flowinfo = 0;
                 sin6->sin6_scope_id = ipv6_iface_scope_id(&sin6->sin6_addr,
                                                           IP6CB(skb)->iif);
+                *addr_len = sizeof(*sin6);
         }
 
         sock_recv_ts_and_drops(msg, sk, skb);
diff --git a/net/ipv6/udp.c b/net/ipv6/udp.c
index f3893e897f72..81eb8cf8389b 100644
--- a/net/ipv6/udp.c
+++ b/net/ipv6/udp.c
@@ -392,9 +392,6 @@ int udpv6_recvmsg(struct kiocb *iocb, struct sock *sk,
         int is_udp4;
         bool slow;
 
-        if (addr_len)
-                *addr_len = sizeof(struct sockaddr_in6);
-
         if (flags & MSG_ERRQUEUE)
                 return ipv6_recv_error(sk, msg, len);
 
@@ -480,7 +477,7 @@ try_again:
                                 ipv6_iface_scope_id(&sin6->sin6_addr,
                                                     IP6CB(skb)->iif);
                 }
-
+                *addr_len = sizeof(*sin6);
         }
         if (is_udp4) {
                 if (inet->cmsg_flags)