ipvs: Fix panic due to non-linear skb

Receiving a ICMP response to an IPIP packet in a non-linear skb could
cause a kernel panic in __skb_pull.

The problem was introduced in
commit f2edb9f7706dcb2c0d9a362b2ba849efe3a97f5e ("ipvs: implement
passive PMTUD for IPIP packets").

Signed-off-by: Peter Christensen <pch@ordbogen.com>
Acked-by: Julian Anastasov <ja@ssi.bg>
Signed-off-by: Simon Horman <horms@verge.net.au>

1 files changed, 10 insertions, 5 deletions

diff --git a/net/netfilter/ipvs/ip_vs_core.c b/net/netfilter/ipvs/ip_vs_core.c
index 4f26ee46b51f..3d2d2c8108ca 100644
--- a/net/netfilter/ipvs/ip_vs_core.c
+++ b/net/netfilter/ipvs/ip_vs_core.c
@@ -1392,15 +1392,19 @@ ip_vs_in_icmp(struct sk_buff *skb, int *related, unsigned int hooknum)
 
         if (ipip) {
                 __be32 info = ic->un.gateway;
+                __u8 type = ic->type;
+                __u8 code = ic->code;
 
                 /* Update the MTU */
                 if (ic->type == ICMP_DEST_UNREACH &&
                     ic->code == ICMP_FRAG_NEEDED) {
                         struct ip_vs_dest *dest = cp->dest;
                         u32 mtu = ntohs(ic->un.frag.mtu);
+                        __be16 frag_off = cih->frag_off;
 
                         /* Strip outer IP and ICMP, go to IPIP header */
-                        __skb_pull(skb, ihl + sizeof(_icmph));
+                        if (pskb_pull(skb, ihl + sizeof(_icmph)) == NULL)
+                                goto ignore_ipip;
                         offset2 -= ihl + sizeof(_icmph);
                         skb_reset_network_header(skb);
                         IP_VS_DBG(12, "ICMP for IPIP %pI4->%pI4: mtu=%u\n",
@@ -1408,7 +1412,7 @@ ip_vs_in_icmp(struct sk_buff *skb, int *related, unsigned int hooknum)
                         ipv4_update_pmtu(skb, dev_net(skb->dev),
                                          mtu, 0, 0, 0, 0);
                         /* Client uses PMTUD? */
-                        if (!(cih->frag_off & htons(IP_DF)))
+                        if (!(frag_off & htons(IP_DF)))
                                 goto ignore_ipip;
                         /* Prefer the resulting PMTU */
                         if (dest) {
@@ -1427,12 +1431,13 @@ ip_vs_in_icmp(struct sk_buff *skb, int *related, unsigned int hooknum)
                 /* Strip outer IP, ICMP and IPIP, go to IP header of
                  * original request.
                  */
-                __skb_pull(skb, offset2);
+                if (pskb_pull(skb, offset2) == NULL)
+                        goto ignore_ipip;
                 skb_reset_network_header(skb);
                 IP_VS_DBG(12, "Sending ICMP for %pI4->%pI4: t=%u, c=%u, i=%u\n",
                         &ip_hdr(skb)->saddr, &ip_hdr(skb)->daddr,
-                        ic->type, ic->code, ntohl(info));
-                icmp_send(skb, ic->type, ic->code, info);
+                        type, code, ntohl(info));
+                icmp_send(skb, type, code, info);
                 /* ICMP can be shorter but anyways, account it */
                 ip_vs_out_stats(cp, skb);