net: rework recvmsg handler msg_name and msg_namelen logic

This patch now always passes msg->msg_namelen as 0. recvmsg handlers must
set msg_namelen to the proper size <= sizeof(struct sockaddr_storage)
to return msg_name to the user.

This prevents numerous uninitialized memory leaks we had in the
recvmsg handlers and makes it harder for new code to accidentally leak
uninitialized memory.

Optimize for the case recvfrom is called with NULL as address. We don't
need to copy the address at all, so set it to NULL before invoking the
recvmsg handler. We can do so, because all the recvmsg handlers must
cope with the case a plain read() is called on them. read() also sets
msg_name to NULL.

Also document these changes in include/linux/net.h as suggested by David
Miller.

Changes since RFC:

Set msg->msg_name = NULL if user specified a NULL in msg_name but had a
non-null msg_namelen in verify_iovec/verify_compat_iovec. This doesn't
affect sendto as it would bail out earlier while trying to copy-in the
address. It also more naturally reflects the logic by the callers of
verify_iovec.

With this change in place I could remove "
if (!uaddr || msg_sys->msg_namelen == 0)
	msg->msg_name = NULL
".

This change does not alter the user visible error logic as we ignore
msg_namelen as long as msg_name is NULL.

Also remove two unnecessary curly brackets in ___sys_recvmsg and change
comments to netdev style.

Cc: David Miller <davem@davemloft.net>
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, 15 insertions, 17 deletions

diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index 2e8286b47c28..61bd50adead1 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -2660,7 +2660,6 @@ static int packet_recvmsg(struct kiocb *iocb, struct socket *sock,
         struct sock *sk = sock->sk;
         struct sk_buff *skb;
         int copied, err;
-        struct sockaddr_ll *sll;
         int vnet_hdr_len = 0;
 
         err = -EINVAL;
@@ -2744,22 +2743,10 @@ static int packet_recvmsg(struct kiocb *iocb, struct socket *sock,
                         goto out_free;
         }
 
-        /*
-         *      If the address length field is there to be filled in, we fill
-         *      it in now.
-         */
-
-        sll = &PACKET_SKB_CB(skb)->sa.ll;
-        if (sock->type == SOCK_PACKET)
-                msg->msg_namelen = sizeof(struct sockaddr_pkt);
-        else
-                msg->msg_namelen = sll->sll_halen + offsetof(struct sockaddr_ll, sll_addr);
-
-        /*
-         *      You lose any data beyond the buffer you gave. If it worries a
-         *      user program they can ask the device for its MTU anyway.
+        /* You lose any data beyond the buffer you gave. If it worries
+         * a user program they can ask the device for its MTU
+         * anyway.
          */
-
         copied = skb->len;
         if (copied > len) {
                 copied = len;
@@ -2772,9 +2759,20 @@ static int packet_recvmsg(struct kiocb *iocb, struct socket *sock,
 
         sock_recv_ts_and_drops(msg, sk, skb);
 
-        if (msg->msg_name)
+        if (msg->msg_name) {
+                /* If the address length field is there to be filled
+                 * in, we fill it in now.
+                 */
+                if (sock->type == SOCK_PACKET) {
+                        msg->msg_namelen = sizeof(struct sockaddr_pkt);
+                } else {
+                        struct sockaddr_ll *sll = &PACKET_SKB_CB(skb)->sa.ll;
+                        msg->msg_namelen = sll->sll_halen +
+                                offsetof(struct sockaddr_ll, sll_addr);
+                }
                 memcpy(msg->msg_name, &PACKET_SKB_CB(skb)->sa,
                        msg->msg_namelen);
+        }
 
         if (pkt_sk(sk)->auxdata) {
                 struct tpacket_auxdata aux;