Subject: [PATCH 21/24] sch_cake: Make sure we can write the IP header before changing DSCP bits

From: Toke Høiland-Jørgensen <[email-masked]>
Date: Thu, 4 Apr 2019 15:01:33 +0200

[ Upstream commit c87b4ecdbe8db27867a7b7f840291cd843406bd7 ]

There is not actually any guarantee that the IP headers are valid before we
access the DSCP bits of the packets. Fix this using the same approach taken
in sch_dsmark.

Reported-by: Kevin Darbyshire-Bryant <[email-masked]>
Signed-off-by: Toke Høiland-Jørgensen <[email-masked]>
---
 net/sched/sch_cake.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/net/sched/sch_cake.c b/net/sched/sch_cake.c
index c5e87d1c26eb..75ca80909cf8 100644
--- a/net/sched/sch_cake.c
+++ b/net/sched/sch_cake.c
@@ -1524,16 +1524,27 @@ static void cake_wash_diffserv(struct sk_buff *skb)
 
 static u8 cake_handle_diffserv(struct sk_buff *skb, u16 wash)
 {
+	int wlen = skb_network_offset(skb);
 	u8 dscp;
 
 	switch (tc_skb_protocol(skb)) {
 	case htons(ETH_P_IP):
+		wlen += sizeof(struct iphdr);
+		if (!pskb_may_pull(skb, wlen) ||
+		    skb_try_make_writable(skb, wlen))
+			return 0;
+
 		dscp = ipv4_get_dsfield(ip_hdr(skb)) >> 2;
 		if (wash && dscp)
 			ipv4_change_dsfield(ip_hdr(skb), INET_ECN_MASK, 0);
 		return dscp;
 
 	case htons(ETH_P_IPV6):
+		wlen += sizeof(struct ipv6hdr);
+		if (!pskb_may_pull(skb, wlen) ||
+		    skb_try_make_writable(skb, wlen))
+			return 0;
+
 		dscp = ipv6_get_dsfield(ipv6_hdr(skb)) >> 2;
 		if (wash && dscp)
 			ipv6_change_dsfield(ipv6_hdr(skb), INET_ECN_MASK, 0);
-- 
2.20.1