pktgen: fix crash when generating IPv6 packets

commit 5aa8b572007c4bca1e6d3dd4c4820f1ae49d6bb2 upstream.

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: David S. Miller <davem@davemloft.net>
Signed-off-by: Cong Wang <amwang@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/net/core/pktgen.c b/net/core/pktgen.c
index df878de7c6ec266dadf4ce9eaee6444abaf5070b..7bc9991f16f1748474def0de912f58c5d7a02634 100644 (file)
--- a/net/core/pktgen.c
+++ b/net/core/pktgen.c
@@ -2935,7 +2935,7 @@ 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);
                if (net_ratelimit())
                        pr_info("increased datalen to %d\n", datalen);