[PATCH] PKT_SCHED: dsmark must take care of shared/cloned skbs

[Thomas Graf <tgraf@xxxxxxx>]

Dave,

Correctly handle shared and cloned skbs by copying them before writing
and dequeue unwriteable skbs unchanged. Assumes that IP/IPv6 header
is always linear so no pulling required.

Signed-off-by: Thomas Graf <tgraf@xxxxxxx>

--- linux-2.6.10-rc3-bk12.orig/net/sched/sch_dsmark.c   2004-12-18 
15:16:29.000000000 +0100
+++ linux-2.6.10-rc3-bk12/net/sched/sch_dsmark.c        2004-12-18 
16:24:58.000000000 +0100
@@ -195,7 +195,8 @@
 
        D2PRINTK("dsmark_enqueue(skb %p,sch %p,[qdisc %p])\n",skb,sch,p);
        if (p->set_tc_index) {
-               /* FIXME: Safe with non-linear skbs? --RR */
+               /* Safe with non-linear skbs? --RR
+                  IP/IPv6 header is always linear --TGR */
                switch (skb->protocol) {
                        case __constant_htons(ETH_P_IP):
                                skb->tc_index = ipv4_get_dsfield(skb->nh.iph);
@@ -250,6 +251,34 @@
        return ret;
 }
 
+static inline int
+dsmark_make_writeable(struct sk_buff **pskb, int offset)
+{
+       struct sk_buff *nskb;
+
+       if ((offset + (*pskb)->mac_len) > (*pskb)->len)
+               return 0;
+
+       if (skb_shared(*pskb) || skb_cloned(*pskb))
+               goto copy_skb;
+
+       /* IP/IPv6 header is always linear, no need to pull */
+       return 1;
+
+copy_skb:
+       nskb = skb_copy(*pskb, GFP_ATOMIC);
+       if (!nskb)
+               return 0;
+       BUG_ON(skb_is_nonlinear(nskb));
+
+       /* Rest of kernel will get very unhappy if we pass it a
+          suddenly-orphaned skbuff */
+       if ((*pskb)->sk)
+               skb_set_owner_w(nskb, (*pskb)->sk);
+       kfree_skb(*pskb);
+       *pskb = nskb;
+       return 1;
+}
 
 static struct sk_buff *dsmark_dequeue(struct Qdisc *sch)
 {
@@ -266,10 +295,14 @@
        D2PRINTK("index %d->%d\n",skb->tc_index,index);
        switch (skb->protocol) {
                case __constant_htons(ETH_P_IP):
+                       if (!dsmark_make_writeable(&skb, sizeof(struct iphdr)))
+                               goto unwriteable;
                        ipv4_change_dsfield(skb->nh.iph,
                            p->mask[index],p->value[index]);
                        break;
                case __constant_htons(ETH_P_IPV6):
+                       if (!dsmark_make_writeable(&skb, sizeof(struct 
ipv6hdr)))
+                               goto unwriteable;
                        ipv6_change_dsfield(skb->nh.ipv6h,
                            p->mask[index],p->value[index]);
                        break;
@@ -280,12 +313,17 @@
                         * and don't need yet another qdisc as a bypass.
                         */
                        if (p->mask[index] != 0xff || p->value[index])
-                               printk(KERN_WARNING "dsmark_dequeue: "
-                                      "unsupported protocol %d\n",
-                                      htons(skb->protocol));
+                               if (net_ratelimit())
+                                       printk(KERN_WARNING "dsmark_dequeue: "
+                                              "unsupported protocol %d\n",
+                                              htons(skb->protocol));
                        break;
        };
        return skb;
+unwriteable:
+       if (net_ratelimit())
+               printk(KERN_WARNING "dsmark_dequeue: skb not writable\n");
+       return skb;
 }