netdev - [Patch nf v2 3/3] xt_hashlimit: limit the max size of hashtable

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Message-Id: <20200203043053.19192-4-xiyou.wangcong@gmail.com>
Date:   Sun,  2 Feb 2020 20:30:53 -0800
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     netdev@...r.kernel.org
Cc:     fw@...len.de, netfilter-devel@...r.kernel.org,
        Cong Wang <xiyou.wangcong@...il.com>,
        syzbot+adf6c6c2be1c3a718121@...kaller.appspotmail.com,
        Pablo Neira Ayuso <pablo@...filter.org>,
        Jozsef Kadlecsik <kadlec@...filter.org>
Subject: [Patch nf v2 3/3] xt_hashlimit: limit the max size of hashtable

The user-specified hashtable size is unbound, this could
easily lead to an OOM or a hung task as we hold the global
mutex while allocating and initializing the new hashtable.

Add a max value to cap both cfg->size and cfg->max, as
suggested by Florian.

Reported-and-tested-by: syzbot+adf6c6c2be1c3a718121@...kaller.appspotmail.com
Cc: Pablo Neira Ayuso <pablo@...filter.org>
Cc: Jozsef Kadlecsik <kadlec@...filter.org>
Cc: Florian Westphal <fw@...len.de>
Signed-off-by: Cong Wang <xiyou.wangcong@...il.com>
---
 net/netfilter/xt_hashlimit.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/net/netfilter/xt_hashlimit.c b/net/netfilter/xt_hashlimit.c
index 06e59f9d9f62..60c023630d14 100644
--- a/net/netfilter/xt_hashlimit.c
+++ b/net/netfilter/xt_hashlimit.c
@@ -837,6 +837,8 @@ hashlimit_mt(const struct sk_buff *skb, struct xt_action_param *par)
 	return hashlimit_mt_common(skb, par, hinfo, &info->cfg, 3);
 }
 
+#define HASHLIMIT_MAX_SIZE 1048576
+
 static int hashlimit_mt_check_common(const struct xt_mtchk_param *par,
 				     struct xt_hashlimit_htable **hinfo,
 				     struct hashlimit_cfg3 *cfg,
@@ -847,6 +849,14 @@ static int hashlimit_mt_check_common(const struct xt_mtchk_param *par,
 
 	if (cfg->gc_interval == 0 || cfg->expire == 0)
 		return -EINVAL;
+	if (cfg->size > HASHLIMIT_MAX_SIZE) {
+		cfg->size = HASHLIMIT_MAX_SIZE;
+		pr_info_ratelimited("size too large, truncated to %u\n", cfg->size);
+	}
+	if (cfg->max > HASHLIMIT_MAX_SIZE) {
+		cfg->max = HASHLIMIT_MAX_SIZE;
+		pr_info_ratelimited("max too large, truncated to %u\n", cfg->max);
+	}
 	if (par->family == NFPROTO_IPV4) {
 		if (cfg->srcmask > 32 || cfg->dstmask > 32)
 			return -EINVAL;
-- 
2.21.1