linux-ext4 - Re: [PATCH 3/3] ext4: correctly detect when an xattr value has an invalid size

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Date:   Thu, 1 Dec 2016 15:00:09 -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 3/3] ext4: correctly detect when an xattr value has an
 invalid size

On Sat, Nov 26, 2016 at 10:39:46PM -0800, Eric Biggers wrote:
> It was possible for an xattr value to have a very large size, which
> would then pass validation on 32-bit architectures due to a pointer
> wraparound.  Fix this by validating the size in a way which avoids
> pointer wraparound.
> 
> It was also possible that a value's size would fit in the available
> space but its padded size would not.  This would cause an out-of-bounds
> memory write in ext4_xattr_set_entry when replacing the xattr value.
> For example, if an xattr value of unpadded size 253 bytes went until the
> very end of the inode or block, then using setxattr(2) to replace this
> xattr's value with 256 bytes would cause a write to the 3 bytes past the
> end of the inode or buffer, and the new xattr value would be incorrectly
> truncated.  Fix this by requiring that the padded size fit in the
> available space rather than the unpadded size.
> 
> This patch shouldn't have any noticeable effect on
> non-corrupted/non-malicious filesystems.
> 
> Signed-off-by: Eric Biggers <ebiggers@...gle.com>

Thanks, applied.

					- Ted
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