sch_cake: Make sure we can write the IP header before changing DSCP bits

There is not actually any guarantee that the IP headers are valid before we
access the DSCP bits of the packets. Fix this using the same approach taken
in sch_dsmark.

Reported-by: Kevin Darbyshire-Bryant <kevin@darbyshire-bryant.me.uk>
Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/sched/sch_cake.c b/net/sched/sch_cake.c
index a3b55e18df047e36bbceb0fe88cdb82f4a164f62..259d97bc2abd39df8df646c2ebc34ea272e1fd70 100644 (file)
--- a/net/sched/sch_cake.c
+++ b/net/sched/sch_cake.c
@@ -1517,16 +1517,27 @@ static unsigned int cake_drop(struct Qdisc *sch, struct sk_buff **to_free)
 
 static u8 cake_handle_diffserv(struct sk_buff *skb, u16 wash)
 {
+       int wlen = skb_network_offset(skb);
        u8 dscp;
 
        switch (tc_skb_protocol(skb)) {
        case htons(ETH_P_IP):
+               wlen += sizeof(struct iphdr);
+               if (!pskb_may_pull(skb, wlen) ||
+                   skb_try_make_writable(skb, wlen))
+                       return 0;
+
                dscp = ipv4_get_dsfield(ip_hdr(skb)) >> 2;
                if (wash && dscp)
                        ipv4_change_dsfield(ip_hdr(skb), INET_ECN_MASK, 0);
                return dscp;
 
        case htons(ETH_P_IPV6):
+               wlen += sizeof(struct ipv6hdr);
+               if (!pskb_may_pull(skb, wlen) ||
+                   skb_try_make_writable(skb, wlen))
+                       return 0;
+
                dscp = ipv6_get_dsfield(ipv6_hdr(skb)) >> 2;
                if (wash && dscp)
                        ipv6_change_dsfield(ipv6_hdr(skb), INET_ECN_MASK, 0);