act_csum: fix possible use after free

tcf_csum_skb_nextlayer() / pskb_may_pull() can change skb->head, so we
must be careful not keeping pointers to previous headers.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Jamal Hadi Salim <jhs@mojatatu.com>
Cc: Grégoire Baron <baronchon@n7mm.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/sched/act_csum.c

@@ -166,15 +166,17 @@ static int tcf_csum_ipv4_igmp(struct sk_buff *skb,
 	return 1;
 }
 
-static int tcf_csum_ipv6_icmp(struct sk_buff *skb, struct ipv6hdr *ip6h,
+static int tcf_csum_ipv6_icmp(struct sk_buff *skb,
 			      unsigned int ihl, unsigned int ipl)
 {
 	struct icmp6hdr *icmp6h;
+	const struct ipv6hdr *ip6h;
 
 	icmp6h = tcf_csum_skb_nextlayer(skb, ihl, ipl, sizeof(*icmp6h));
 	if (icmp6h == NULL)
 		return 0;
 
+	ip6h = ipv6_hdr(skb);
 	icmp6h->icmp6_cksum = 0;
 	skb->csum = csum_partial(icmp6h, ipl - ihl, 0);
 	icmp6h->icmp6_cksum = csum_ipv6_magic(&ip6h->saddr, &ip6h->daddr,
@@ -186,15 +188,17 @@ static int tcf_csum_ipv6_icmp(struct sk_buff *skb, struct ipv6hdr *ip6h,
 	return 1;
 }
 
-static int tcf_csum_ipv4_tcp(struct sk_buff *skb, struct iphdr *iph,
+static int tcf_csum_ipv4_tcp(struct sk_buff *skb,
 			     unsigned int ihl, unsigned int ipl)
 {
 	struct tcphdr *tcph;
+	const struct iphdr *iph;
 
 	tcph = tcf_csum_skb_nextlayer(skb, ihl, ipl, sizeof(*tcph));
 	if (tcph == NULL)
 		return 0;
 
+	iph = ip_hdr(skb);
 	tcph->check = 0;
 	skb->csum = csum_partial(tcph, ipl - ihl, 0);
 	tcph->check = tcp_v4_check(ipl - ihl,
@@ -205,15 +209,17 @@ static int tcf_csum_ipv4_tcp(struct sk_buff *skb, struct iphdr *iph,
 	return 1;
 }
 
-static int tcf_csum_ipv6_tcp(struct sk_buff *skb, struct ipv6hdr *ip6h,
+static int tcf_csum_ipv6_tcp(struct sk_buff *skb,
 			     unsigned int ihl, unsigned int ipl)
 {
 	struct tcphdr *tcph;
+	const struct ipv6hdr *ip6h;
 
 	tcph = tcf_csum_skb_nextlayer(skb, ihl, ipl, sizeof(*tcph));
 	if (tcph == NULL)
 		return 0;
 
+	ip6h = ipv6_hdr(skb);
 	tcph->check = 0;
 	skb->csum = csum_partial(tcph, ipl - ihl, 0);
 	tcph->check = csum_ipv6_magic(&ip6h->saddr, &ip6h->daddr,
@@ -225,10 +231,11 @@ static int tcf_csum_ipv6_tcp(struct sk_buff *skb, struct ipv6hdr *ip6h,
 	return 1;
 }
 
-static int tcf_csum_ipv4_udp(struct sk_buff *skb, struct iphdr *iph,
+static int tcf_csum_ipv4_udp(struct sk_buff *skb,
 			     unsigned int ihl, unsigned int ipl, int udplite)
 {
 	struct udphdr *udph;
+	const struct iphdr *iph;
 	u16 ul;
 
 	/*
@@ -242,6 +249,7 @@ static int tcf_csum_ipv4_udp(struct sk_buff *skb, struct iphdr *iph,
 	if (udph == NULL)
 		return 0;
 
+	iph = ip_hdr(skb);
 	ul = ntohs(udph->len);
 
 	if (udplite || udph->check) {
@@ -276,10 +284,11 @@ ignore_obscure_skb:
 	return 1;
 }
 
-static int tcf_csum_ipv6_udp(struct sk_buff *skb, struct ipv6hdr *ip6h,
+static int tcf_csum_ipv6_udp(struct sk_buff *skb,
 			     unsigned int ihl, unsigned int ipl, int udplite)
 {
 	struct udphdr *udph;
+	const struct ipv6hdr *ip6h;
 	u16 ul;
 
 	/*
@@ -293,6 +302,7 @@ static int tcf_csum_ipv6_udp(struct sk_buff *skb, struct ipv6hdr *ip6h,
 	if (udph == NULL)
 		return 0;
 
+	ip6h = ipv6_hdr(skb);
 	ul = ntohs(udph->len);
 
 	udph->check = 0;
@@ -328,7 +338,7 @@ ignore_obscure_skb:
 
 static int tcf_csum_ipv4(struct sk_buff *skb, u32 update_flags)
 {
-	struct iphdr *iph;
+	const struct iphdr *iph;
 	int ntkoff;
 
 	ntkoff = skb_network_offset(skb);
@@ -353,19 +363,19 @@ static int tcf_csum_ipv4(struct sk_buff *skb, u32 update_flags)
 		break;
 	case IPPROTO_TCP:
 		if (update_flags & TCA_CSUM_UPDATE_FLAG_TCP)
-			if (!tcf_csum_ipv4_tcp(skb, iph, iph->ihl * 4,
+			if (!tcf_csum_ipv4_tcp(skb, iph->ihl * 4,
 					       ntohs(iph->tot_len)))
 				goto fail;
 		break;
 	case IPPROTO_UDP:
 		if (update_flags & TCA_CSUM_UPDATE_FLAG_UDP)
-			if (!tcf_csum_ipv4_udp(skb, iph, iph->ihl * 4,
+			if (!tcf_csum_ipv4_udp(skb, iph->ihl * 4,
 					       ntohs(iph->tot_len), 0))
 				goto fail;
 		break;
 	case IPPROTO_UDPLITE:
 		if (update_flags & TCA_CSUM_UPDATE_FLAG_UDPLITE)
-			if (!tcf_csum_ipv4_udp(skb, iph, iph->ihl * 4,
+			if (!tcf_csum_ipv4_udp(skb, iph->ihl * 4,
 					       ntohs(iph->tot_len), 1))
 				goto fail;
 		break;
@@ -377,7 +387,7 @@ static int tcf_csum_ipv4(struct sk_buff *skb, u32 update_flags)
 		    pskb_expand_head(skb, 0, 0, GFP_ATOMIC))
 			goto fail;
 
-		ip_send_check(iph);
+		ip_send_check(ip_hdr(skb));
 	}
 
 	return 1;
@@ -456,6 +466,7 @@ static int tcf_csum_ipv6(struct sk_buff *skb, u32 update_flags)
 			ixhl = ipv6_optlen(ip6xh);
 			if (!pskb_may_pull(skb, hl + ixhl + ntkoff))
 				goto fail;
+			ip6xh = (void *)(skb_network_header(skb) + hl);
 			if ((nexthdr == NEXTHDR_HOP) &&
 			    !(tcf_csum_ipv6_hopopts(ip6xh, ixhl, &pl)))
 				goto fail;
@@ -464,25 +475,25 @@ static int tcf_csum_ipv6(struct sk_buff *skb, u32 update_flags)
 			break;
 		case IPPROTO_ICMPV6:
 			if (update_flags & TCA_CSUM_UPDATE_FLAG_ICMP)
-				if (!tcf_csum_ipv6_icmp(skb, ip6h,
+				if (!tcf_csum_ipv6_icmp(skb,
 							hl, pl + sizeof(*ip6h)))
 					goto fail;
 			goto done;
 		case IPPROTO_TCP:
 			if (update_flags & TCA_CSUM_UPDATE_FLAG_TCP)
-				if (!tcf_csum_ipv6_tcp(skb, ip6h,
+				if (!tcf_csum_ipv6_tcp(skb,
 						       hl, pl + sizeof(*ip6h)))
 					goto fail;
 			goto done;
 		case IPPROTO_UDP:
 			if (update_flags & TCA_CSUM_UPDATE_FLAG_UDP)
-				if (!tcf_csum_ipv6_udp(skb, ip6h, hl,
+				if (!tcf_csum_ipv6_udp(skb, hl,
 						       pl + sizeof(*ip6h), 0))
 					goto fail;
 			goto done;
 		case IPPROTO_UDPLITE:
 			if (update_flags & TCA_CSUM_UPDATE_FLAG_UDPLITE)
-				if (!tcf_csum_ipv6_udp(skb, ip6h, hl,
+				if (!tcf_csum_ipv6_udp(skb, hl,
 						       pl + sizeof(*ip6h), 1))
 					goto fail;
 			goto done;