linux-kernel - [PATCH v2] lib/checksum.c: fix carry in csum_tcpudp

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Message-Id: <1422439091-31413-1-git-send-email-karl.beldan@rivierawaves.com>
Date:	Wed, 28 Jan 2015 10:58:11 +0100
From:	Karl Beldan <karl.beldan@...il.com>
To:	unlisted-recipients:; (no To-header on input)
Cc:	Karl Beldan <karl.beldan@...il.com>,
	Karl Beldan <karl.beldan@...ierawaves.com>,
	Al Viro <viro@...IV.linux.org.uk>,
	Eric Dumazet <eric.dumazet@...il.com>,
	Arnd Bergmann <arnd@...db.de>,
	Mike Frysinger <vapier@...too.org>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: [PATCH v2] lib/checksum.c: fix carry in csum_tcpudp_nofold

The carry from the 64->32bits folding was dropped, e.g with:
saddr=0xFFFFFFFF daddr=0xFF0000FF len=0xFFFF proto=0 sum=1,
csum_tcpudp_nofold returned 0 instead of 1.

Signed-off-by: Karl Beldan <karl.beldan@...ierawaves.com>
Cc: Al Viro <viro@...IV.linux.org.uk>
Cc: Eric Dumazet <eric.dumazet@...il.com>
Cc: Arnd Bergmann <arnd@...db.de>
Cc: Mike Frysinger <vapier@...too.org>
Cc: netdev@...r.kernel.org
Cc: linux-kernel@...r.kernel.org
Cc: stable@...r.kernel.org
---
 lib/checksum.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/lib/checksum.c b/lib/checksum.c
index 129775e..fcf3894 100644
--- a/lib/checksum.c
+++ b/lib/checksum.c
@@ -47,6 +47,15 @@ static inline unsigned short from32to16(unsigned int x)
 	return x;
 }
 
+static inline u32 from64to32(u64 x)
+{
+	/* add up 32-bit and 32-bit for 32+c bit */
+	x = (x & 0xffffffff) + (x >> 32);
+	/* add up carry.. */
+	x = (x & 0xffffffff) + (x >> 32);
+	return (u32)x;
+}
+
 static unsigned int do_csum(const unsigned char *buff, int len)
 {
 	int odd;
@@ -195,8 +204,7 @@ __wsum csum_tcpudp_nofold(__be32 saddr, __be32 daddr,
 #else
 	s += (proto + len) << 8;
 #endif
-	s += (s >> 32);
-	return (__force __wsum)s;
+	return (__force __wsum)from64to32(s);
 }
 EXPORT_SYMBOL(csum_tcpudp_nofold);
 #endif
-- 
2.0.1

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