RE: [PATCH] parisc: Fix csum_ipv6_magic on 32-bit systems

David Laight
2024-02-11T13:57:36Z

From: Guenter Roeck
> Sent: 10 February 2024 19:16
>
> Calculating the IPv6 checksum on 32-bit systems missed overflows when
> adding the proto+len fields into the checksum. This results in the
> following unit test failure.
>
> # test_csum_ipv6_magic: ASSERTION FAILED at lib/checksum_kunit.c:506
> Expected ( u64)csum_result == ( u64)expected, but
> ( u64)csum_result == 46722 (0xb682)
> ( u64)expected == 46721 (0xb681)
> not ok 5 test_csum_ipv6_magic
>
> This is probably rarely seen in the real world because proto+len are
> usually small values which will rarely result in overflows when calculating
> the checksum. However, the unit test code uses large values for the length
> field, causing the test to fail.

Isn't length limited by the protocol encoding?
So this is really a bug in the unit tests for using a length that
it too large for the function?

David

>
> Fix the problem by adding the missing carry into the final checksum.
>
> Cc: Charlie Jenkins <charlie@rivosinc.com>
> Cc: Palmer Dabbelt <palmer@rivosinc.com>
> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> Signed-off-by: Guenter Roeck <linux@roeck-us.net>
> ---
> arch/parisc/include/asm/checksum.h | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/arch/parisc/include/asm/checksum.h b/arch/parisc/include/asm/checksum.h
> index f705e5dd1074..e619e67440db 100644
> --- a/arch/parisc/include/asm/checksum.h
> +++ b/arch/parisc/include/asm/checksum.h
> @@ -163,7 +163,8 @@ static __inline__ __sum16 csum_ipv6_magic(const struct in6_addr *saddr,
> " ldw,ma 4(%2), %7\n" /* 4th daddr */
> " addc %6, %0, %0\n"
> " addc %7, %0, %0\n"
> -" addc %3, %0, %0\n" /* fold in proto+len, catch carry */
> +" addc %3, %0, %0\n" /* fold in proto+len */
> +" addc 0, %0, %0\n" /* add carry */
>
> #endif
> : "=r" (sum), "=r" (saddr), "=r" (daddr), "=r" (len),
> --
> 2.39.2
>

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