From: Arnd Bergmann <arnd@arndb.de>
To: Pablo Neira Ayuso <pablo@netfilter.org>,
        Jozsef Kadlecsik <kadlec@blackhole.kfki.hu>,
        Florian Westphal <fw@strlen.de>,
        "David S. Miller" <davem@davemloft.net>
Cc: Arnd Bergmann <arnd@arndb.de>, Vishwanath Pai <vpai@akamai.com>,
        Josh Hunt <johunt@akamai.com>, netfilter-devel@vger.kernel.org,
        coreteam@netfilter.org, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: [PATCH] netfilter: xt_hashlimit: avoid 64-bit division
Date: Wed,  6 Sep 2017 21:57:30 +0200
Message-Id: <20170906195825.3715290-1-arnd@arndb.de>
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1076
Lines: 34

64-bit division is expensive on 32-bit architectures, and
requires a special function call to avoid a link error like:

net/netfilter/xt_hashlimit.o: In function `hashlimit_mt_common':
xt_hashlimit.c:(.text+0x1328): undefined reference to `__aeabi_uldivmod'

In the case of hashlimit_mt_common, we don't actually need a
64-bit operation, we can simply rewrite the function slightly
to make that clear to the compiler.

Fixes: bea74641e378 ("netfilter: xt_hashlimit: add rate match mode")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
 net/netfilter/xt_hashlimit.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/net/netfilter/xt_hashlimit.c b/net/netfilter/xt_hashlimit.c
index 10d48234f5f4..50b53d86eef5 100644
--- a/net/netfilter/xt_hashlimit.c
+++ b/net/netfilter/xt_hashlimit.c
@@ -531,7 +531,10 @@ static u64 user2rate_bytes(u64 user)
 {
 	u64 r;
 
-	r = user ? 0xFFFFFFFFULL / user : 0xFFFFFFFFULL;
+	if (user > 0xFFFFFFFFULL)
+		return 0;
+
+	r = user ? 0xFFFFFFFFULL / (u32)user : 0xFFFFFFFFULL;
 	r = (r - 1) << 4;
 	return r;
 }
-- 
2.9.0