[NETFILTER]: ipt_REJECT: fix memory corruption

On devices with hard_header_len > LL_MAX_HEADER ip_route_me_harder()
reallocates the skb, leading to memory corruption when using the stale
tcph pointer to update the checksum.

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 9 insertions, 7 deletions

diff --git a/net/ipv4/netfilter/ipt_REJECT.c b/net/ipv4/netfilter/ipt_REJECT.c
index ad0312d0e4fd..264763adc39b 100644
--- a/net/ipv4/netfilter/ipt_REJECT.c
+++ b/net/ipv4/netfilter/ipt_REJECT.c
@@ -114,6 +114,14 @@ static void send_reset(struct sk_buff *oldskb, int hook)
         tcph->window = 0;
         tcph->urg_ptr = 0;
 
+        /* Adjust TCP checksum */
+        tcph->check = 0;
+        tcph->check = tcp_v4_check(tcph, sizeof(struct tcphdr),
+                                   nskb->nh.iph->saddr,
+                                   nskb->nh.iph->daddr,
+                                   csum_partial((char *)tcph,
+                                                sizeof(struct tcphdr), 0));
+
         /* Set DF, id = 0 */
         nskb->nh.iph->frag_off = htons(IP_DF);
         nskb->nh.iph->id = 0;
@@ -129,14 +137,8 @@ static void send_reset(struct sk_buff *oldskb, int hook)
         if (ip_route_me_harder(&nskb, addr_type))
                 goto free_nskb;
 
-        /* Adjust TCP checksum */
         nskb->ip_summed = CHECKSUM_NONE;
-        tcph->check = 0;
-        tcph->check = tcp_v4_check(tcph, sizeof(struct tcphdr),
-                                   nskb->nh.iph->saddr,
-                                   nskb->nh.iph->daddr,
-                                   csum_partial((char *)tcph,
-                                                sizeof(struct tcphdr), 0));
+
         /* Adjust IP TTL */
         nskb->nh.iph->ttl = dst_metric(nskb->dst, RTAX_HOPLIMIT);