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

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Date:   Mon, 12 Apr 2021 08:48:08 -0700
From:   "Darrick J. Wong" <djwong@...nel.org>
To:     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 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.

> > +/*
> > + * 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.

--D

> > +					 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.