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.

The max value is derived from the max value when chosen by
the kernel.

Reported-and-tested-by: syzbot+adf6c6c2be1c3a718121@syzkaller.appspotmail.com
Cc: Pablo Neira Ayuso <pablo@netfilter.org>
Cc: Jozsef Kadlecsik <redacted>
Cc: Florian Westphal <fw@strlen.de>
Signed-off-by: Cong Wang <redacted>
---
 net/netfilter/xt_hashlimit.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/net/netfilter/xt_hashlimit.c b/net/netfilter/xt_hashlimit.c
index 57a2639bcc22..6327134c5886 100644
--- a/net/netfilter/xt_hashlimit.c
+++ b/net/netfilter/xt_hashlimit.c

@@ -272,6 +272,8 @@ dsthash_free(struct xt_hashlimit_htable *ht, struct dsthash_ent *ent)
 }
 static void htable_gc(struct work_struct *work);
 
+#define HASHLIMIT_MAX_SIZE 8192
+
 static int htable_create(struct net *net, struct hashlimit_cfg3 *cfg,
 			 const char *name, u_int8_t family,
 			 struct xt_hashlimit_htable **out_hinfo,

@@ -290,7 +292,7 @@ static int htable_create(struct net *net, struct hashlimit_cfg3 *cfg,
 		size = (nr_pages << PAGE_SHIFT) / 16384 /
 		       sizeof(struct hlist_head);
 		if (nr_pages > 1024 * 1024 * 1024 / PAGE_SIZE)
-			size = 8192;
+			size = HASHLIMIT_MAX_SIZE;
 		if (size < 16)
 			size = 16;
 	}

@@ -848,6 +850,8 @@ 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)
+		return -ENOMEM;