From: Antonio Messina <amessina@google.com>
Date: Thu, 19 Dec 2019 15:08:03 +0100
Subject: udp: fix integer overflow while computing available space in
 sk_rcvbuf
Git-commit: feed8a4fc9d46c3126fb9fcae0e9248270c6321a
Patch-mainline: 5.5-rc5
References: networking-stable-20_01_01

When the size of the receive buffer for a socket is close to 2^31 when
computing if we have enough space in the buffer to copy a packet from
the queue to the buffer we might hit an integer overflow.

When an user set net.core.rmem_default to a value close to 2^31 UDP
packets are dropped because of this overflow. This can be visible, for
instance, with failure to resolve hostnames.

This can be fixed by casting sk_rcvbuf (which is an int) to unsigned
int, similarly to how it is done in TCP.

Signed-off-by: Antonio Messina <amessina@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
---
 net/ipv4/udp.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -1283,7 +1283,7 @@ int __udp_enqueue_schedule_skb(struct so
 	 * queue contains some other skb
 	 */
 	rmem = atomic_add_return(size, &sk->sk_rmem_alloc);
-	if (rmem > (size + sk->sk_rcvbuf))
+	if (rmem > (size + (unsigned int)sk->sk_rcvbuf))
 		goto uncharge_drop;
 
 	spin_lock(&list->lock);