sch_dsmark: fix invalid skb_cow() usage

commit aea92fb2e09e29653b023d4254ac9fbf94221538 upstream.

skb_cow(skb, sizeof(ip header)) is not very helpful in this context.

First we need to use pskb_may_pull() to make sure the ip header
is in skb linear part, then use skb_try_make_writable() to
address clones issues.

Fixes: 4c30719f4f55 ("[PKT_SCHED] dsmark: handle cloned and non-linear skb's")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/net/sched/sch_dsmark.c b/net/sched/sch_dsmark.c
index d75bfcf..fb24bb4 100644 (file)
--- a/net/sched/sch_dsmark.c
+++ b/net/sched/sch_dsmark.c
@@ -202,9 +202,13 @@ static int dsmark_enqueue(struct sk_buff *skb, struct Qdisc *sch)
        pr_debug("dsmark_enqueue(skb %p,sch %p,[qdisc %p])\n", skb, sch, p);
 
        if (p->set_tc_index) {
+               int wlen = skb_network_offset(skb);
+
                switch (skb->protocol) {
                case htons(ETH_P_IP):
-                       if (skb_cow_head(skb, sizeof(struct iphdr)))
+                       wlen += sizeof(struct iphdr);
+                       if (!pskb_may_pull(skb, wlen) ||
+                           skb_try_make_writable(skb, wlen))
                                goto drop;
 
                        skb->tc_index = ipv4_get_dsfield(ip_hdr(skb))
@@ -212,7 +216,9 @@ static int dsmark_enqueue(struct sk_buff *skb, struct Qdisc *sch)
                        break;
 
                case htons(ETH_P_IPV6):
-                       if (skb_cow_head(skb, sizeof(struct ipv6hdr)))
+                       wlen += sizeof(struct ipv6hdr);
+                       if (!pskb_may_pull(skb, wlen) ||
+                           skb_try_make_writable(skb, wlen))
                                goto drop;
 
                        skb->tc_index = ipv6_get_dsfield(ipv6_hdr(skb))