From: Behan Webster <behanw@converseincode.com>
To: Theodore Ts'o <tytso@mit.edu>
Cc: linux-ext4@vger.kernel.org, Mark Charlebois <charlebm@gmail.com>
Subject: Re: [PATCH] Remove VLAIS usage from JBD2 code
Date: Tue, 30 Oct 2012 15:02:43 -0400 [thread overview]
Message-ID: <50902453.9090404@converseincode.com> (raw)
In-Reply-To: <20121030190032.GB5044@thunk.org>
On 12-10-30 03:00 PM, Theodore Ts'o wrote:
> On Tue, Oct 30, 2012 at 02:40:04PM -0400, Behan Webster wrote:
>> From: Mark Charlebois <charlebm@gmail.com>
>>
>> The use of variable length arrays in structs (VLAIS) in the Linux Kernel code
>> precludes the use of compilers which don't implement VLAIS (for instance the
>> Clang compiler). Since ctx is always a 32-bit CRC, hard coding a size of 4
>> bytes accomplishes the same thing without the use of VLAIS. This is the same
>> technique already employed in fs/ext4/ext4.h
>>
>> Signed-off-by: Mark Charlebois <charlebm@gmail.com>
>> Signed-off-by: Behan Webster <behanw@converseincode.com>
> That's reasonable, but in order to be safe to make sure we don't
> accidentally introduce a stack overrun bug at some point in the
> future, we should do something like this instead
>
> + #define JBD_MAX_CHECKSUM_SIZE 4
> .
> .
> .
>
> - char ctx[crypto_shash_descsize(journal->j_chksum_driver)];
> + char ctx[JBD_MAX_CHECKSUM_SIZE];
> .
> .
> .
> + BUG_ON(crypto_shash_descsize(journal->j_chksum_driver) >
> + JBD_MAX_CHECKSUM_SIZE);
>
>
> I just like being careful and paranoid; using magic numeric constants
> for buffer sizes is just a scary thing to do. If you could resubmit
> the patch with this change, I'd really appreciate it. Thanks!!
A very good idea. Will do. Expect it soon.
Behan
--
Behan Webster
behanw@converseincode.com
next prev parent reply other threads:[~2012-10-30 19:02 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-10-30 18:40 [PATCH] Removing the use of VLAIS from the Linux Kernel Behan Webster
2012-10-30 18:40 ` [PATCH] Remove VLAIS usage from JBD2 code Behan Webster
2012-10-30 19:00 ` Theodore Ts'o
2012-10-30 19:02 ` Behan Webster [this message]
2012-10-30 19:13 ` Darrick J. Wong
2012-11-08 15:53 ` Theodore Ts'o
2012-11-09 23:19 ` Darrick J. Wong
2012-11-09 23:24 ` Darrick J. Wong
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