linux-kernel - [PATCH 5.4 125/135] netfilter: xt_hashlimit: limit the max size of hashtable

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Message-Id: <20200227132247.854451211@linuxfoundation.org>
Date:   Thu, 27 Feb 2020 14:37:45 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Cong Wang <xiyou.wangcong@...il.com>,
        Florian Westphal <fw@...len.de>,
        Pablo Neira Ayuso <pablo@...filter.org>,
        syzbot+adf6c6c2be1c3a718121@...kaller.appspotmail.com
Subject: [PATCH 5.4 125/135] netfilter: xt_hashlimit: limit the max size of hashtable

From: Cong Wang <xiyou.wangcong@...il.com>

commit 8d0015a7ab76b8b1e89a3e5f5710a6e5103f2dd5 upstream.

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
Signed-off-by: Cong Wang <xiyou.wangcong@...il.com>
Reviewed-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/xt_hashlimit.c |   10 ++++++++++
 1 file changed, 10 insertions(+)

--- a/net/netfilter/xt_hashlimit.c
+++ b/net/netfilter/xt_hashlimit.c
@@ -851,6 +851,8 @@ hashlimit_mt(const struct sk_buff *skb,
 	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,
@@ -861,6 +863,14 @@ static int hashlimit_mt_check_common(con
 
 	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;