net/sched: act_mpls: ensure LSE is pullable before reading it

when 'act_mpls' is used to mangle the LSE, the current value is read from
the packet dereferencing 4 bytes at mpls_hdr(): ensure that the label is
contained in the skb "linear" area.

Found by code inspection.

v2:
 - use MPLS_HLEN instead of sizeof(new_lse), thanks to Jakub Kicinski

Fixes: 2a2ea50870ba ("net: sched: add mpls manipulation actions to TC")
Signed-off-by: Davide Caratti <dcaratti@redhat.com>
Acked-by: Guillaume Nault <gnault@redhat.com>
Link: https://lore.kernel.org/r/3243506cba43d14858f3bd21ee0994160e44d64a.1606987058.git.dcaratti@redhat.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/net/sched/act_mpls.c b/net/sched/act_mpls.c
index 5c7456e5b5cf04643c5421a05467092c75398f44..d1486ea496a2cacaa6c141f12c13b3210743ecb7 100644 (file)
--- a/net/sched/act_mpls.c
+++ b/net/sched/act_mpls.c
@@ -105,6 +105,9 @@ static int tcf_mpls_act(struct sk_buff *skb, const struct tc_action *a,
                        goto drop;
                break;
        case TCA_MPLS_ACT_MODIFY:
+               if (!pskb_may_pull(skb,
+                                  skb_network_offset(skb) + MPLS_HLEN))
+                       goto drop;
                new_lse = tcf_mpls_get_lse(mpls_hdr(skb), p, false);
                if (skb_mpls_update_lse(skb, new_lse))
                        goto drop;