packet: fix tp_reserve race in packet_set_ring

Updates to tp_reserve can race with reads of the field in
packet_set_ring. Avoid this by holding the socket lock during
updates in setsockopt PACKET_RESERVE.

This bug was discovered by syzkaller.

Fixes: 8913336a7e8d ("packet: add PACKET_RESERVE sockopt")
Reported-by: Andrey Konovalov <andreyknvl@google.com>
Signed-off-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
CVE-2017-1000111

(cherry-picked from commit c27927e372f0785f3303e8fad94b85945e2c97b7)
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>

diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index 0f074c96f43f9eff16a22c2757e7d4ddbed6c661..ede751d2f44ee36325d36b8853a01b2317eaccea 100644 (file)
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -3640,14 +3640,19 @@ packet_setsockopt(struct socket *sock, int level, int optname, char __user *optv
 
                if (optlen != sizeof(val))
                        return -EINVAL;
-               if (po->rx_ring.pg_vec || po->tx_ring.pg_vec)
-                       return -EBUSY;
                if (copy_from_user(&val, optval, sizeof(val)))
                        return -EFAULT;
                if (val > INT_MAX)
                        return -EINVAL;
-               po->tp_reserve = val;
-               return 0;
+               lock_sock(sk);
+               if (po->rx_ring.pg_vec || po->tx_ring.pg_vec) {
+                       ret = -EBUSY;
+               } else {
+                       po->tp_reserve = val;
+                       ret = 0;
+               }
+               release_sock(sk);
+               return ret;
        }
        case PACKET_LOSS:
        {