netfilter: 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@syzkaller.appspotmail.com
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Reviewed-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

diff --git a/net/netfilter/xt_hashlimit.c b/net/netfilter/xt_hashlimit.c
index cc475a6..7a2c4b8 100644 (file)
--- 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;