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

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Date:   Mon, 12 Apr 2021 10:36:51 -0500
From:   "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To:     Christoph Hellwig <hch@...radead.org>,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>
Cc:     "Darrick J. Wong" <djwong@...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 10:29, 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.
> 
>> +/*
>> + * 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.

This was proposed by Darrick[1]. However, I'm curious, why do you think
they are "completely silly"?

> 
>> -					(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),
>> +					 0, 0, NULL);
>>  	if (!xfs_efd_zone)
>>  		goto out_destroy_buf_item_zone;
>>  
>>  	xfs_efi_zone = kmem_cache_create("xfs_efi_item",
>> -					 (sizeof(struct xfs_efi_log_item) +
>> -					 (XFS_EFI_MAX_FAST_EXTENTS - 1) *
>> -					 sizeof(struct xfs_extent)),
>> +					 struct_size((struct xfs_efi_log_item *)0,
>> +					 efi_format.efi_extents,
>> +					 XFS_EFI_MAX_FAST_EXTENTS),
> 
> Same here.  And this obsfucated version also adds completely pointless
> overly long lines while making the code unreadable.

This could actually use one of the inline helpers you think are silly. :)

Thanks
--
Gustavo

[1] https://lore.kernel.org/lkml/20210311031745.GT3419940@magnolia/