linux-hardening - Re: [PATCH v4][next] xfs: Replace one-element arrays with flexible-array members

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Date:   Mon, 12 Apr 2021 10:57:07 -0500
From:   "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To:     "Darrick J. Wong" <djwong@...nel.org>,
        Christoph Hellwig <hch@...radead.org>
Cc:     "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        linux-xfs@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-hardening@...r.kernel.org
Subject: Re: [PATCH v4][next] xfs: Replace one-element arrays with
 flexible-array members



On 4/12/21 10:48, Darrick J. Wong wrote:
> On Mon, Apr 12, 2021 at 04:29:06PM +0100, Christoph Hellwig wrote:
>>> Below are the results of running xfstests for "all" with the following
>>> configuration in local.config:
>>
>> ...
>>
>>> Other tests might need to be run in order to verify everything is working
>>> as expected. For such tests, the intervention of the maintainers might be
>>> needed.
>>
>> This is a little weird for a commit log.  If you want to show results
>> this would be something that goes into a cover letter.
> 
> Agreed, please don't post fstests output in the commit message.

OK. I've got it.

> 
>>> +/*
>>> + * Calculates the size of structure xfs_efi_log_format followed by an
>>> + * array of n number of efi_extents elements.
>>> + */
>>> +static inline size_t
>>> +sizeof_efi_log_format(size_t n)
>>> +{
>>> +	return struct_size((struct xfs_efi_log_format *)0, efi_extents, n);
>>
>> These helpers are completely silly.  Just keep the existing open code
>> version using sizeof with the one-off removed.
> 
> A couple of revisions ago I specifically asked Gustavo to create these
> 'silly' sizeof helpers to clean up...
> 
>>> -					(sizeof(struct xfs_efd_log_item) +
>>> -					(XFS_EFD_MAX_FAST_EXTENTS - 1) *
>>> -					sizeof(struct xfs_extent)),
>>> -					0, 0, NULL);
>>> +					 struct_size((struct xfs_efd_log_item *)0,
>>> +					 efd_format.efd_extents,
>>> +					 XFS_EFD_MAX_FAST_EXTENTS),
> 
> ...these even uglier multiline statements.  I was also going to ask for
> these kmem cache users to get cleaned up.  I'd much rather look at:
> 
> 	xfs_efi_zone = kmem_cache_create("xfs_efi_item",
> 				sizeof_xfs_efi(XFS_EFI_MAX_FAST_EXTENTS), 0);
> 	if (!xfs_efi_zone)
> 		goto the_drop_zone;
> 
> even if it means another static inline.

Yep; I agree[1].

Thanks
--
Gustavo

[1] https://lore.kernel.org/lkml/63078523-8a57-36f4-228b-1594f0e3b025@embeddedor.com/