mpls: Properly validate RTA_VIA payload length

If the nla length is less than 2 then the nla data could be accessed
beyond the accessible bounds. So ensure that the nla is big enough to
at least read the via_family before doing so. Replace magic value of
2.

Fixes: 03c0566542f4 ("mpls: Basic support for adding and removing routes")
Cc: Eric W. Biederman <[email protected]>
Signed-off-by: Robert Shearman <[email protected]>
Acked-by: "Eric W. Biederman" <[email protected]>
Signed-off-by: David S. Miller <[email protected]>

diff --git a/net/mpls/af_mpls.c b/net/mpls/af_mpls.c
index 20cf48a8593d00388dc4f110897353111b2d2ce6..4f265c677ecac8b877f8db44b187c37017d3f223 100644 (file)
--- a/net/mpls/af_mpls.c
+++ b/net/mpls/af_mpls.c
@@ -586,8 +586,11 @@ static int rtm_to_route_config(struct sk_buff *skb,  struct nlmsghdr *nlh,
                case RTA_VIA:
                {
                        struct rtvia *via = nla_data(nla);
+                       if (nla_len(nla) < offsetof(struct rtvia, rtvia_addr))
+                               goto errout;
                        cfg->rc_via_family = via->rtvia_family;
-                       cfg->rc_via_alen   = nla_len(nla) - 2;
+                       cfg->rc_via_alen   = nla_len(nla) -
+                               offsetof(struct rtvia, rtvia_addr);
                        if (cfg->rc_via_alen > MAX_VIA_ALEN)
                                goto errout;