net: ipmr/ip6mr: fix potential out-of-bounds vif_table access

mfc_parent of cache entries is used to index into the vif_table and is
initialised from mfcctl->mfcc_parent. This can take values of to 2^16-1,
while the vif_table has only MAXVIFS (32) entries. The same problem
affects ip6mr.

Refuse invalid values to fix a potential out-of-bounds access. Unlike
the other validity checks, this is checked in ipmr_mfc_add() instead of
the setsockopt handler since its unused in the delete path and might be
uninitialized.

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 3 insertions, 0 deletions

diff --git a/net/ipv6/ip6mr.c b/net/ipv6/ip6mr.c
index 52e0f74fdfe0..23e4ac0cc30e 100644
--- a/net/ipv6/ip6mr.c
+++ b/net/ipv6/ip6mr.c
@@ -1113,6 +1113,9 @@ static int ip6mr_mfc_add(struct net *net, struct mf6cctl *mfc, int mrtsock)
         unsigned char ttls[MAXMIFS];
         int i;
 
+        if (mfc->mf6cc_parent >= MAXMIFS)
+                return -ENFILE;
+
         memset(ttls, 255, MAXMIFS);
         for (i = 0; i < MAXMIFS; i++) {
                 if (IF_ISSET(i, &mfc->mf6cc_ifset))