linux-ext4 - Re: [PATCH 1/3] ext4: forbid i_extra

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Date:   Thu, 1 Dec 2016 14:49:07 -0500
From:   Theodore Ts'o <tytso@....edu>
To:     Eric Biggers <ebiggers@...gle.com>
Cc:     linux-ext4@...r.kernel.org,
        Andreas Dilger <adilger.kernel@...ger.ca>
Subject: Re: [PATCH 1/3] ext4: forbid i_extra_isize not divisible by 4

On Sat, Nov 26, 2016 at 10:39:44PM -0800, Eric Biggers wrote:
> i_extra_isize not divisible by 4 is problematic for several reasons:
> 
> - It causes the in-inode xattr space to be misaligned, but the xattr
>   header and entries are not declared __packed to express this
>   possibility.  This may cause poor performance or incorrect code
>   generation on some platforms.
> - When validating the xattr entries we can read past the end of the
>   inode if the size available for xattrs is not a multiple of 4.
> - It allows the nonsensical i_extra_isize=1, which doesn't even leave
>   enough room for i_extra_isize itself.
> 
> Therefore, update ext4_iget() to consider i_extra_isize not divisible by
> 4 to be an error, like the case where i_extra_isize is too large.
> 
> This also matches the rule recently added to e2fsck for determining
> whether an inode has valid i_extra_isize.
> 
> This patch shouldn't have any noticeable effect on
> non-corrupted/non-malicious filesystems, since the size of ext4_inode
> has always been a multiple of 4.
> 
> Signed-off-by: Eric Biggers <ebiggers@...gle.com>

Thanks, applied.

					- Ted
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