net: ipmr/ip6mr: prevent out-of-bounds vif_table access

When cache is unresolved, c->mf[6]c_parent is set to 65535 and
minvif, maxvif are not initialized, hence we must avoid to
parse IIF and OIF.
A second problem can happen when the user dumps a cache entry
where a VIF, that was referenced at creation time, has been
removed.

Signed-off-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 7 insertions, 4 deletions

diff --git a/net/ipv4/ipmr.c b/net/ipv4/ipmr.c
index 0b9d03c54dc3..d0a6092a67be 100644
--- a/net/ipv4/ipmr.c
+++ b/net/ipv4/ipmr.c
@@ -1616,17 +1616,20 @@ ipmr_fill_mroute(struct sk_buff *skb, struct mfc_cache *c, struct rtmsg *rtm)
         int ct;
         struct rtnexthop *nhp;
         struct net *net = mfc_net(c);
-        struct net_device *dev = net->ipv4.vif_table[c->mfc_parent].dev;
         u8 *b = skb_tail_pointer(skb);
         struct rtattr *mp_head;
 
-        if (dev)
-                RTA_PUT(skb, RTA_IIF, 4, &dev->ifindex);
+        /* If cache is unresolved, don't try to parse IIF and OIF */
+        if (c->mfc_parent > MAXVIFS)
+                return -ENOENT;
+
+        if (VIF_EXISTS(net, c->mfc_parent))
+                RTA_PUT(skb, RTA_IIF, 4, &net->ipv4.vif_table[c->mfc_parent].dev->ifindex);
 
         mp_head = (struct rtattr *)skb_put(skb, RTA_LENGTH(0));
 
         for (ct = c->mfc_un.res.minvif; ct < c->mfc_un.res.maxvif; ct++) {
-                if (c->mfc_un.res.ttls[ct] < 255) {
+                if (VIF_EXISTS(net, ct) && c->mfc_un.res.ttls[ct] < 255) {
                         if (skb_tailroom(skb) < RTA_ALIGN(RTA_ALIGN(sizeof(*nhp)) + 4))
                                 goto rtattr_failure;
                         nhp = (struct rtnexthop *)skb_put(skb, RTA_ALIGN(sizeof(*nhp)));