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 <ebiederm@xmission.com>
Signed-off-by: Robert Shearman <rshearma@brocade.com>
Acked-by: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 4 insertions, 1 deletions

diff --git a/net/mpls/af_mpls.c b/net/mpls/af_mpls.c
index 20cf48a8593d..4f265c677eca 100644
--- 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;