net: avoid signed overflows for SO_{SND|RCV}BUFFORCE

CAP_NET_ADMIN users should not be allowed to set negative
sk_sndbuf or sk_rcvbuf values, as it can lead to various memory
corruptions, crashes, OOM...

Note that before commit 82981930125a ("net: cleanups in
sock_setsockopt()"), the bug was even more serious, since SO_SNDBUF
and SO_RCVBUF were vulnerable.

This needs to be backported to all known linux kernels.

Again, many thanks to syzkaller team for discovering this gem.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: Andrey Konovalov <andreyknvl@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/core/sock.c b/net/core/sock.c
index 5e3ca414357e2404db28eeacc5e9306051161493..00a074dbfe9bf169c2b81498e6ae265199745b22 100644 (file)
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -715,7 +715,7 @@ int sock_setsockopt(struct socket *sock, int level, int optname,
                val = min_t(u32, val, sysctl_wmem_max);
 set_sndbuf:
                sk->sk_userlocks |= SOCK_SNDBUF_LOCK;
-               sk->sk_sndbuf = max_t(u32, val * 2, SOCK_MIN_SNDBUF);
+               sk->sk_sndbuf = max_t(int, val * 2, SOCK_MIN_SNDBUF);
                /* Wake up sending tasks if we upped the value. */
                sk->sk_write_space(sk);
                break;
@@ -751,7 +751,7 @@ set_rcvbuf:
                 * returning the value we actually used in getsockopt
                 * is the most desirable behavior.
                 */
-               sk->sk_rcvbuf = max_t(u32, val * 2, SOCK_MIN_RCVBUF);
+               sk->sk_rcvbuf = max_t(int, val * 2, SOCK_MIN_RCVBUF);
                break;
 
        case SO_RCVBUFFORCE: