[PATCH 4.19 21/96] sch_cake: Make sure we can write the IP header before changing DSCP bits

[Greg Kroah-Hartman]

From: Toke Høiland-Jørgensen <t...@redhat.com>

[ 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 <ke...@darbyshire-bryant.me.uk>
Signed-off-by: Toke Høiland-Jørgensen <t...@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>
---
 net/sched/sch_cake.c |   11 +++++++++++
 1 file changed, 11 insertions(+)

--- a/net/sched/sch_cake.c
+++ b/net/sched/sch_cake.c
@@ -1524,16 +1524,27 @@ static void cake_wash_diffserv(struct sk
 
 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);