pktgen: fix crash when generating IPv6 packets

For IPv6, sizeof(struct ipv6hdr) = 40, thus the following
expression will result negative:

        datalen = pkt_dev->cur_pkt_size - 14 -
                  sizeof(struct ipv6hdr) - sizeof(struct udphdr) -
                  pkt_dev->pkt_overhead;

And,  the check "if (datalen < sizeof(struct pktgen_hdr))" will be
passed as "datalen" is promoted to unsigned, therefore will cause
a crash later.

This is a quick fix by checking if "datalen" is negative. The following
patch will increase the default value of 'min_pkt_size' for IPv6.

This bug should exist for a long time, so Cc -stable too.

Cc: <stable@vger.kernel.org>
Cc: David S. Miller <davem@davemloft.net>
Signed-off-by: Cong Wang <amwang@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/core/pktgen.c b/net/core/pktgen.c
index 148e73d2c4515d777d577733f32205c38d03932e..e356b8d52bad12bd2dae3fc24af6b39e2a20b548 100644 (file)
--- a/net/core/pktgen.c
+++ b/net/core/pktgen.c
@@ -2927,7 +2927,7 @@ static struct sk_buff *fill_packet_ipv6(struct net_device *odev,
                  sizeof(struct ipv6hdr) - sizeof(struct udphdr) -
                  pkt_dev->pkt_overhead;
 
-       if (datalen < sizeof(struct pktgen_hdr)) {
+       if (datalen < 0 || datalen < sizeof(struct pktgen_hdr)) {
                datalen = sizeof(struct pktgen_hdr);
                net_info_ratelimited("increased datalen to %d\n", datalen);
        }