netfilter: xt_sctp: validate the flag_info count

sctp_mt_check doesn't validate the flag_count field. An attacker can
take advantage of that to trigger a OOB read and leak memory
information.

Add the field validation in the checkentry function.

Fixes: 2e4e6a17af35 ("[NETFILTER] x_tables: Abstraction layer for {ip,ip6,arp}_tables")
Cc: stable@vger.kernel.org
Reported-by: Lucas Leong <wmliang@infosec.exchange>
Signed-off-by: Wander Lairson Costa <wander@redhat.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

diff --git a/net/netfilter/xt_sctp.c b/net/netfilter/xt_sctp.c
index e8961094a2822d991868a318d1ab88a814b45578..b46a6a51205833bb6688d400755a76c3c744bb14 100644 (file)
--- a/net/netfilter/xt_sctp.c
+++ b/net/netfilter/xt_sctp.c
@@ -149,6 +149,8 @@ static int sctp_mt_check(const struct xt_mtchk_param *par)
 {
        const struct xt_sctp_info *info = par->matchinfo;
 
+       if (info->flag_count > ARRAY_SIZE(info->flag_info))
+               return -EINVAL;
        if (info->flags & ~XT_SCTP_VALID_FLAGS)
                return -EINVAL;
        if (info->invflags & ~XT_SCTP_VALID_FLAGS)