linux-kernel - Re: [PATCH] eCryptfs: Check array bounds for filename characters

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Message-ID: <20111123170350.GA24836@boyd>
Date:	Wed, 23 Nov 2011 11:03:59 -0600
From:	Tyler Hicks <tyhicks@...onical.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Michael Halcrow <mhalcrow@...gle.com>, ecryptfs@...r.kernel.org,
	linux-kernel@...r.kernel.org, thieule@...gle.com
Subject: Re: [PATCH] eCryptfs: Check array bounds for filename characters

On 2011-11-21 16:49:07, Linus Torvalds wrote:
> On Mon, Nov 21, 2011 at 3:32 PM, Michael Halcrow <mhalcrow@...gle.com> wrote:
> > Characters with ASCII values greater than the size of
> > filename_rev_map[] are valid filename
> > characters. ecryptfs_decode_from_filename() will access kernel memory
> > beyond that array, and ecryptfs_parse_tag_70_packet() will then
> > decrypt those characters.
> 
> Ugh. I really don't like the patch.
> 
> Why isn't the patch just this one-liner:
> 
>   diff --git a/fs/ecryptfs/crypto.c b/fs/ecryptfs/crypto.c
>   index 58609bde3b9f..7c50715c05d6 100644
>   --- a/fs/ecryptfs/crypto.c
>   +++ b/fs/ecryptfs/crypto.c
>   @@ -1943,7 +1943,7 @@ static unsigned char *portable_filename_chars
> = ("-.0123456789ABCD"
> 
>    /* We could either offset on every reverse map or just pad some 0x00's
>     * at the front here */
>   -static const unsigned char filename_rev_map[] = {
>   +static const unsigned char filename_rev_map[256] = {
>           0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, /* 7 */
>           0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, /* 15 */
>           0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, /* 23 */
> 
> instead?
> 
> Making invalid characters over \x50 be somehow magically different
> from invalid characters elsewhere seems just totally bogus. There are
> lots of characters that aren't valid, and they have the
> filename_rev_map[] value of 0 elsewhere.
> 
> So the simpler one-liner is not only simpler, but gives much saner
> semantics, I think - now invalid character '\x05' gets exactly the
> same result as invalid character '\xf5'.

Good point - I'll get this in proper patch form and send a pull request
your way, along with a couple of other fixes.

Tyler

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