Revert "Revert "ipv4: fix memory leaks in ip_cmsg_send() callers""

This reverts commit d7807a9a.

As mentioned in https://lkml.org/lkml/2021/9/13/1819
5 years old commit 91948309 ("ipv4: fix memory leaks in ip_cmsg_send() callers")
was a correct fix.

  ip_cmsg_send() can loop over multiple cmsghdr()

  If IP_RETOPTS has been successful, but following cmsghdr generates an error,
  we do not free ipc.ok

  If IP_RETOPTS is not successful, we have freed the allocated temporary space,
  not the one currently in ipc.opt.

Sure, code could be refactored, but let's not bring back old bugs.

Fixes: d7807a9a ("Revert "ipv4: fix memory leaks in ip_cmsg_send() callers"")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Yajun Deng <yajun.deng@linux.dev>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/ip_sockglue.c

@@ -279,7 +279,7 @@ int ip_cmsg_send(struct sock *sk, struct msghdr *msg, struct ipcm_cookie *ipc,
 		case IP_RETOPTS:
 			err = cmsg->cmsg_len - sizeof(struct cmsghdr);
 
-			/* Our caller is responsible for freeing ipc->opt when err = 0 */
+			/* Our caller is responsible for freeing ipc->opt */
 			err = ip_options_get(net, &ipc->opt,
 					     KERNEL_SOCKPTR(CMSG_DATA(cmsg)),
 					     err < 40 ? err : 40);

net/ipv4/ping.c

@@ -727,9 +727,10 @@ static int ping_v4_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
 
 	if (msg->msg_controllen) {
 		err = ip_cmsg_send(sk, msg, &ipc, false);
-		if (unlikely(err))
+		if (unlikely(err)) {
+			kfree(ipc.opt);
 			return err;
-
+		}
 		if (ipc.opt)
 			free = 1;
 	}

net/ipv4/raw.c

@@ -562,9 +562,10 @@ static int raw_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
 
 	if (msg->msg_controllen) {
 		err = ip_cmsg_send(sk, msg, &ipc, false);
-		if (unlikely(err))
+		if (unlikely(err)) {
+			kfree(ipc.opt);
 			goto out;
-
+		}
 		if (ipc.opt)
 			free = 1;
 	}

net/ipv4/udp.c

@@ -1122,9 +1122,10 @@ int udp_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
 		if (err > 0)
 			err = ip_cmsg_send(sk, msg, &ipc,
 					   sk->sk_family == AF_INET6);
-		if (unlikely(err < 0))
+		if (unlikely(err < 0)) {
+			kfree(ipc.opt);
 			return err;
-
+		}
 		if (ipc.opt)
 			free = 1;
 		connected = 0;