From: Michael Ellerman <mpe@ellerman.id.au>
To: Paul Mackerras <paulus@ozlabs.org>, linuxppc-dev@ozlabs.org
Subject: Re: [PATCH 1/2] powerpc/64: Fix checksum folding in csum_tcpudp_nofold and ip_fast_csum_nofold
Date: Tue, 08 Nov 2016 18:23:30 +1100 [thread overview]
Message-ID: <878tsul9jh.fsf@concordia.ellerman.id.au> (raw)
In-Reply-To: <20161103051055.GA8368@fergus.ozlabs.ibm.com>
Paul Mackerras <paulus@ozlabs.org> writes:
> These functions compute an IP checksum by computing a 64-bit sum and
> folding it to 32 bits (the "nofold" in their names refers to folding
> down to 16 bits). However, doing (u32) (s + (s >> 32)) is not
> sufficient to fold a 64-bit sum to 32 bits correctly. The addition
> can produce a carry out from bit 31, which needs to be added in to
> the sum to produce the correct result.
>
> To fix this, we copy the from64to32() function from lib/checksum.c
> and use that.
This seems to have been broken since ~forever. Do we just not hit that
case very often, or do we just incorrectly report checksum failures?
Should it go to stable?
cheers
next prev parent reply other threads:[~2016-11-08 7:23 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-11-03 5:10 [PATCH 1/2] powerpc/64: Fix checksum folding in csum_tcpudp_nofold and ip_fast_csum_nofold Paul Mackerras
2016-11-03 5:15 ` [PATCH 2/2] powerpc/64: Use optimized checksum routines on little-endian Paul Mackerras
2017-01-27 0:40 ` [2/2] " Michael Ellerman
2016-11-08 7:23 ` Michael Ellerman [this message]
2016-11-08 22:05 ` [PATCH 1/2] powerpc/64: Fix checksum folding in csum_tcpudp_nofold and ip_fast_csum_nofold Paul Mackerras
2016-12-02 9:44 ` Michael Ellerman
2017-01-27 0:40 ` [1/2] " Michael Ellerman
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