[PATCH 3.2 051/101] MIPS: Fix special case in 64 bit IP checksumming.

[Ben Hutchings]

3.2.89-rc1 review patch.  If anyone has any objections, please let me know.

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

From: Ralf Baechle <ralf@xxxxxxxxxxxxxx>

commit 66fd848cadaa6be974a8c780fbeb328f0af4d3bd upstream.

For certain arguments such as saddr = 0xc0a8fd60, daddr = 0xc0a8fda1,
len = 80, proto = 17, sum = 0x7eae049d there will be a carry when
folding the intermediate 64 bit checksum to 32 bit but the code doesn't
add the carry back to the one's complement sum, thus an incorrect result
will be generated.

Reported-by: Mark Zhang <bomb.zhang@xxxxxxxxx>
Signed-off-by: Ralf Baechle <ralf@xxxxxxxxxxxxxx>
Reviewed-by: James Hogan <james.hogan@xxxxxxxxxx>
Signed-off-by: James Hogan <james.hogan@xxxxxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 arch/mips/include/asm/checksum.h | 2 ++
 1 file changed, 2 insertions(+)

--- a/arch/mips/include/asm/checksum.h
+++ b/arch/mips/include/asm/checksum.h
@@ -155,7 +155,9 @@ static inline __wsum csum_tcpudp_nofold(
 	"	daddu	%0, %4		\n"
 	"	dsll32	$1, %0, 0	\n"
 	"	daddu	%0, $1		\n"
+	"	sltu	$1, %0, $1	\n"
 	"	dsra32	%0, %0, 0	\n"
+	"	addu	%0, $1		\n"
 #endif
 	"	.set	pop"
 	: "=r" (sum)