[PATCH] netfilter: ipset: harden payload calculation in call_ad()

[David Baum <davidbaum461@gmail.com>]

call_ad() computes the netlink error payload size with
min(SIZE_MAX, sizeof(*errmsg) + nlmsg_len(nlh)), but min(SIZE_MAX, x)
is always x, so the guard is a no-op.

Replace it with an explicit negative-length check and
check_add_overflow() so the addition is validated before being passed
to nlmsg_new().

Signed-off-by: David Baum <davidbaum461@gmail.com>
---
 net/netfilter/ipset/ip_set_core.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/net/netfilter/ipset/ip_set_core.c b/net/netfilter/ipset/ip_set_core.c
index a2fe711cb5e3..11d3854d9b11 100644
--- a/net/netfilter/ipset/ip_set_core.c
+++ b/net/netfilter/ipset/ip_set_core.c
@@ -10,6 +10,7 @@
 #include <linux/module.h>
 #include <linux/moduleparam.h>
 #include <linux/ip.h>
+#include <linux/overflow.h>
 #include <linux/skbuff.h>
 #include <linux/spinlock.h>
 #include <linux/rculist.h>
@@ -1763,13 +1764,18 @@ call_ad(struct net *net, struct sock *ctnl, struct sk_buff *skb,
 		struct nlmsghdr *rep, *nlh = nlmsg_hdr(skb);
 		struct sk_buff *skb2;
 		struct nlmsgerr *errmsg;
-		size_t payload = min(SIZE_MAX,
-				     sizeof(*errmsg) + nlmsg_len(nlh));
+		int nlmsg_payload_len = nlmsg_len(nlh);
+		size_t payload;
 		int min_len = nlmsg_total_size(sizeof(struct nfgenmsg));
 		struct nlattr *cda[IPSET_ATTR_CMD_MAX + 1];
 		struct nlattr *cmdattr;
 		u32 *errline;
 
+		if (nlmsg_payload_len < 0 ||
+		    check_add_overflow(sizeof(*errmsg),
+				       (size_t)nlmsg_payload_len, &payload))
+			return -ENOMEM;
+
 		skb2 = nlmsg_new(payload, GFP_KERNEL);
 		if (!skb2)
 			return -ENOMEM;
-- 
2.50.1 (Apple Git-155)