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From: Eric Biggers <ebiggers@google.com>
To: Andreas Dilger <adilger@dilger.ca>
Cc: linux-ext4@vger.kernel.org, Theodore Ts'o <tytso@mit.edu>,
	Andreas Dilger <adilger.kernel@dilger.ca>
Subject: Re: [PATCH 3/3] ext4: correctly detect when an xattr value has an invalid size
Date: Mon, 28 Nov 2016 15:50:35 -0800	[thread overview]
Message-ID: <20161128235035.GC145516@google.com> (raw)
In-Reply-To: <ED9B2B5D-25DD-4D4A-9F1C-86656B154AA8@dilger.ca>

On Mon, Nov 28, 2016 at 12:50:02PM -0700, Andreas Dilger wrote:
> On Nov 26, 2016, at 11:39 PM, Eric Biggers <ebiggers@google.com> 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 isn't actually possible for a valid xattr value to be very large.
> At most 65536 bytes even with large blocks, so it might be easier to
> directly check that e_value_size is not too large rather than trying
> to deal with values of 0xfffffffe bytes or similar?
> 

I suppose we could do something like

	EXT4_XATTR_SIZE(size) > end - value || size > EXT4_MAX_BLOCK_SIZE

instead of

	size > end - value || EXT4_XATTR_SIZE(size) > end - value

But I don't think it's really any better.

Eric

  reply	other threads:[~2016-11-28 23:50 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-11-27  6:39 [PATCH 1/3] ext4: forbid i_extra_isize not divisible by 4 Eric Biggers
2016-11-27  6:39 ` [PATCH 2/3] ext4: don't read out of bounds when checking for in-inode xattrs Eric Biggers
2016-11-28 19:43   ` Andreas Dilger
2016-12-01 19:52   ` Theodore Ts'o
2016-11-27  6:39 ` [PATCH 3/3] ext4: correctly detect when an xattr value has an invalid size Eric Biggers
2016-11-28 19:50   ` Andreas Dilger
2016-11-28 23:50     ` Eric Biggers [this message]
2016-12-01 20:00   ` Theodore Ts'o
2016-11-28 19:30 ` [PATCH 1/3] ext4: forbid i_extra_isize not divisible by 4 Andreas Dilger
2016-12-01 19:49 ` Theodore Ts'o

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