Subject: [PATCH 3.10 07/17] lib/checksum.c: fix carry in csum_tcpudp_nofold

From: Greg Kroah-Hartman <[email-masked]>
Date: Mon, 9 Feb 2015 16:33:34 +0800

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

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

From: karl beldan <[email-masked]>

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 <[email-masked]>
Cc: Al Viro <[email-masked]>
Cc: Eric Dumazet <[email-masked]>
Cc: Arnd Bergmann <[email-masked]>
Cc: Mike Frysinger <[email-masked]>
Cc: [email-masked]
Cc: [email-masked]
Signed-off-by: Eric Dumazet <[email-masked]>
Signed-off-by: David S. Miller <[email-masked]>
Signed-off-by: Greg Kroah-Hartman <[email-masked]>

---
 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