[PATCH 2/2] netlink: Bounds-check struct nlmsgerr creation

[Kees Cook]

For 32-bit systems, it might be possible to wrap lnmsgerr content
lengths beyond SIZE_MAX. Explicitly test for all overflows, and mark the
memcpy() as being unable to internally diagnose overflows.

This also excludes netlink from the coming runtime bounds check on
memcpy(), since it's an unusual case of open-coded sizing and
allocation.

Cc: Pablo Neira Ayuso <pablo@xxxxxxxxxxxxx>
Cc: Jozsef Kadlecsik <kadlec@xxxxxxxxxxxxx>
Cc: Florian Westphal <fw@xxxxxxxxx>
Cc: "David S. Miller" <davem@xxxxxxxxxxxxx>
Cc: Eric Dumazet <edumazet@xxxxxxxxxx>
Cc: Jakub Kicinski <kuba@xxxxxxxxxx>
Cc: Paolo Abeni <pabeni@xxxxxxxxxx>
Cc: syzbot <syzkaller@xxxxxxxxxxxxxxxx>
Cc: netfilter-devel@xxxxxxxxxxxxxxx
Cc: coreteam@xxxxxxxxxxxxx
Cc: netdev@xxxxxxxxxxxxxxx
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
---
 net/netfilter/ipset/ip_set_core.c | 10 +++++--
 net/netlink/af_netlink.c          | 49 +++++++++++++++++++++----------
 2 files changed, 40 insertions(+), 19 deletions(-)

diff --git a/net/netfilter/ipset/ip_set_core.c b/net/netfilter/ipset/ip_set_core.c
index 16ae92054baa..43576f68f53d 100644
--- a/net/netfilter/ipset/ip_set_core.c
+++ b/net/netfilter/ipset/ip_set_core.c
@@ -1709,13 +1709,14 @@ 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));
+		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 (check_add_overflow(sizeof(*errmsg), nlmsg_len(nlh), &payload))
+			return -ENOMEM;
 		skb2 = nlmsg_new(payload, GFP_KERNEL);
 		if (!skb2)
 			return -ENOMEM;
@@ -1723,7 +1724,10 @@ call_ad(struct net *net, struct sock *ctnl, struct sk_buff *skb,
 				  nlh->nlmsg_seq, NLMSG_ERROR, payload, 0);
 		errmsg = nlmsg_data(rep);
 		errmsg->error = ret;
-		memcpy(&errmsg->msg, nlh, nlh->nlmsg_len);
+		unsafe_memcpy(&errmsg->msg, nlh, nlh->nlmsg_len,
+			      /* "payload" was explicitly bounds-checked, based on
+			       * the size of nlh->nlmsg_len.
+			       */);
 		cmdattr = (void *)&errmsg->msg + min_len;
 
 		ret = nla_parse(cda, IPSET_ATTR_CMD_MAX, cmdattr,
diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index 0cd91f813a3b..8779c273f34f 100644
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -2407,7 +2407,7 @@ void netlink_ack(struct sk_buff *in_skb, struct nlmsghdr *nlh, int err,
 	struct nlmsghdr *rep;
 	struct nlmsgerr *errmsg;
 	size_t payload = sizeof(*errmsg);
-	size_t tlvlen = 0;
+	size_t alloc_size, tlvlen = 0;
 	struct netlink_sock *nlk = nlk_sk(NETLINK_CB(in_skb).sk);
 	unsigned int flags = 0;
 	bool nlk_has_extack = nlk->flags & NETLINK_F_EXT_ACK;
@@ -2419,32 +2419,44 @@ void netlink_ack(struct sk_buff *in_skb, struct nlmsghdr *nlh, int err,
 	if (nlk_has_extack && extack && extack->_msg)
 		tlvlen += nla_total_size(strlen(extack->_msg) + 1);
 
-	if (err && !(nlk->flags & NETLINK_F_CAP_ACK))
-		payload += nlmsg_len(nlh);
+	if (err && !(nlk->flags & NETLINK_F_CAP_ACK) &&
+	    check_add_overflow(payload, (size_t)nlmsg_len(nlh), &payload))
+		goto failure;
 	else
 		flags |= NLM_F_CAPPED;
-	if (err && nlk_has_extack && extack && extack->bad_attr)
-		tlvlen += nla_total_size(sizeof(u32));
-	if (nlk_has_extack && extack && extack->cookie_len)
-		tlvlen += nla_total_size(extack->cookie_len);
-	if (err && nlk_has_extack && extack && extack->policy)
-		tlvlen += netlink_policy_dump_attr_size_estimate(extack->policy);
+	if (err && nlk_has_extack && extack && extack->bad_attr &&
+	    check_add_overflow(tlvlen, (size_t)nla_total_size(sizeof(u32)),
+			       &tlvlen))
+		goto failure;
+	if (nlk_has_extack && extack && extack->cookie_len &&
+	    check_add_overflow(tlvlen, (size_t)nla_total_size(extack->cookie_len),
+			       &tlvlen))
+		goto failure;
+	if (err && nlk_has_extack && extack && extack->policy &&
+	    check_add_overflow(tlvlen,
+			       (size_t)netlink_policy_dump_attr_size_estimate(extack->policy),
+			       &tlvlen))
+		goto failure;
 
 	if (tlvlen)
 		flags |= NLM_F_ACK_TLVS;
 
-	skb = nlmsg_new(payload + tlvlen, GFP_KERNEL);
-	if (!skb) {
-		NETLINK_CB(in_skb).sk->sk_err = ENOBUFS;
-		sk_error_report(NETLINK_CB(in_skb).sk);
-		return;
-	}
+	if (check_add_overflow(payload, tlvlen, &alloc_size))
+		goto failure;
+
+	skb = nlmsg_new(alloc_size, GFP_KERNEL);
+	if (!skb)
+		goto failure;
 
 	rep = __nlmsg_put(skb, NETLINK_CB(in_skb).portid, nlh->nlmsg_seq,
 			  NLMSG_ERROR, payload, flags);
 	errmsg = nlmsg_data(rep);
 	errmsg->error = err;
-	memcpy(&errmsg->msg, nlh, payload > sizeof(*errmsg) ? nlh->nlmsg_len : sizeof(*nlh));
+	unsafe_memcpy(&errmsg->msg, nlh, payload > sizeof(*errmsg)
+					 ?  nlh->nlmsg_len : sizeof(*nlh),
+		      /* "payload" was bounds checked against nlh->nlmsg_len,
+		       * and overflow-checked as tlvlen was constructed.
+		       */);
 
 	if (nlk_has_extack && extack) {
 		if (extack->_msg) {
@@ -2469,6 +2481,11 @@ void netlink_ack(struct sk_buff *in_skb, struct nlmsghdr *nlh, int err,
 	nlmsg_end(skb, rep);
 
 	nlmsg_unicast(in_skb->sk, skb, NETLINK_CB(in_skb).portid);
+	return;
+failure:
+	NETLINK_CB(in_skb).sk->sk_err = ENOBUFS;
+	sk_error_report(NETLINK_CB(in_skb).sk);
+
 }
 EXPORT_SYMBOL(netlink_ack);
 
-- 
2.34.1