linux-kernel - [PATCH 3.18 20/39] lib/checksum.c: fix carry in csum_tcpudp

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Message-Id: <20150209083329.724014541@linuxfoundation.org>
Date:	Mon,  9 Feb 2015 16:34:03 +0800
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org, 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,
	Eric Dumazet <edumazet@...gle.com>,
	"David S. Miller" <davem@...emloft.net>
Subject: [PATCH 3.18 20/39] lib/checksum.c: fix carry in csum_tcpudp_nofold

3.18-stable review patch.  If anyone has any objections, please let me know.

------------------

From: karl beldan <karl.beldan@...il.com>

commit 150ae0e94634714b23919f0c333fee28a5b199d5 upstream.

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
Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 lib/checksum.c |   12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

--- a/lib/checksum.c
+++ b/lib/checksum.c
@@ -47,6 +47,15 @@ static inline unsigned short from32to16(
 	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,
 #else
 	s += (proto + len) << 8;
 #endif
-	s += (s >> 32);
-	return (__force __wsum)s;
+	return (__force __wsum)from64to32(s);
 }
 EXPORT_SYMBOL(csum_tcpudp_nofold);
 #endif


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