linux-kernel - [PATCH 4.9 16/87] netfilter: nf_tables: cant fail after linking rule into active rule list

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Date:   Mon, 21 May 2018 23:10:52 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Florian Westphal <fw@...len.de>,
        Pablo Neira Ayuso <pablo@...filter.org>
Subject: [PATCH 4.9 16/87] netfilter: nf_tables: cant fail after linking rule into active rule list

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Florian Westphal <fw@...len.de>

commit 569ccae68b38654f04b6842b034aa33857f605fe upstream.

rules in nftables a free'd using kfree, but protected by rcu, i.e. we
must wait for a grace period to elapse.

Normal removal patch does this, but nf_tables_newrule() doesn't obey
this rule during error handling.

It calls nft_trans_rule_add() *after* linking rule, and, if that
fails to allocate memory, it unlinks the rule and then kfree() it --
this is unsafe.

Switch order -- first add rule to transaction list, THEN link it
to public list.

Note: nft_trans_rule_add() uses GFP_KERNEL; it will not fail so this
is not a problem in practice (spotted only during code review).

Fixes: 0628b123c96d12 ("netfilter: nfnetlink: add batch support and use it from nf_tables")
Signed-off-by: Florian Westphal <fw@...len.de>
Signed-off-by: Pablo Neira Ayuso <pablo@...filter.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 net/netfilter/nf_tables_api.c |   59 ++++++++++++++++++++++--------------------
 1 file changed, 32 insertions(+), 27 deletions(-)

--- a/net/netfilter/nf_tables_api.c
+++ b/net/netfilter/nf_tables_api.c
@@ -2200,41 +2200,46 @@ static int nf_tables_newrule(struct net
 	}
 
 	if (nlh->nlmsg_flags & NLM_F_REPLACE) {
-		if (nft_is_active_next(net, old_rule)) {
-			trans = nft_trans_rule_add(&ctx, NFT_MSG_DELRULE,
-						   old_rule);
-			if (trans == NULL) {
-				err = -ENOMEM;
-				goto err2;
-			}
-			nft_deactivate_next(net, old_rule);
-			chain->use--;
-			list_add_tail_rcu(&rule->list, &old_rule->list);
-		} else {
+		if (!nft_is_active_next(net, old_rule)) {
 			err = -ENOENT;
 			goto err2;
 		}
-	} else if (nlh->nlmsg_flags & NLM_F_APPEND)
-		if (old_rule)
-			list_add_rcu(&rule->list, &old_rule->list);
-		else
-			list_add_tail_rcu(&rule->list, &chain->rules);
-	else {
-		if (old_rule)
-			list_add_tail_rcu(&rule->list, &old_rule->list);
-		else
-			list_add_rcu(&rule->list, &chain->rules);
-	}
+		trans = nft_trans_rule_add(&ctx, NFT_MSG_DELRULE,
+					   old_rule);
+		if (trans == NULL) {
+			err = -ENOMEM;
+			goto err2;
+		}
+		nft_deactivate_next(net, old_rule);
+		chain->use--;
+
+		if (nft_trans_rule_add(&ctx, NFT_MSG_NEWRULE, rule) == NULL) {
+			err = -ENOMEM;
+			goto err2;
+		}
 
-	if (nft_trans_rule_add(&ctx, NFT_MSG_NEWRULE, rule) == NULL) {
-		err = -ENOMEM;
-		goto err3;
+		list_add_tail_rcu(&rule->list, &old_rule->list);
+	} else {
+		if (nft_trans_rule_add(&ctx, NFT_MSG_NEWRULE, rule) == NULL) {
+			err = -ENOMEM;
+			goto err2;
+		}
+
+		if (nlh->nlmsg_flags & NLM_F_APPEND) {
+			if (old_rule)
+				list_add_rcu(&rule->list, &old_rule->list);
+			else
+				list_add_tail_rcu(&rule->list, &chain->rules);
+		 } else {
+			if (old_rule)
+				list_add_tail_rcu(&rule->list, &old_rule->list);
+			else
+				list_add_rcu(&rule->list, &chain->rules);
+		}
 	}
 	chain->use++;
 	return 0;
 
-err3:
-	list_del_rcu(&rule->list);
 err2:
 	nf_tables_rule_destroy(&ctx, rule);
 err1: