[PATCH 4.14 77/91] udp: fix integer overflow while computing available space in sk_rcvbuf

Greg Kroah-Hartman
2020-01-02T22:49:53Z

From: Antonio Messina <amessina@google.com>

[ Upstream commit feed8a4fc9d46c3126fb9fcae0e9248270c6321a ]

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: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/ipv4/udp.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -1338,7 +1338,7 @@ 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);