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From: Eric Biggers <ebiggers@kernel.org>
To: Aaro Koskinen <aaro.koskinen@iki.fi>
Cc: David Howells <dhowells@redhat.com>,
	"Theodore Y. Ts'o" <tytso@mit.edu>,
	Jaegeuk Kim <jaegeuk@kernel.org>,
	linux-fscrypt@vger.kernel.org, linux-kernel@vger.kernel.org,
	keyrings@vger.kernel.org
Subject: Re: Bug report: unaligned access with ext4 encryption
Date: Thu, 10 Jan 2019 15:01:14 -0800	[thread overview]
Message-ID: <20190110230114.GF149637@gmail.com> (raw)
In-Reply-To: <20190110222928.GB22416@darkstar.musicnaut.iki.fi>

On Fri, Jan 11, 2019 at 12:29:28AM +0200, Aaro Koskinen wrote:
> Hi,
> 
> On Fri, Jan 04, 2019 at 05:28:02PM +0000, David Howells wrote:
> > Eric Biggers <ebiggers@kernel.org> wrote:
> > > Hi Aaro, thanks for the bug report!  I think you're on the right track; it makes
> > > much more sense to have the keyrings subsystem store the payload with better
> > > alignment, than to work around the 2-byte alignment in fscrypt.
> > > 
> > > But how about '__aligned(__alignof__(u64))' instead?  4 bytes may not be enough.
> > > 
> > > David, what do you think?
> > 
> > Does that even work?
> 
> That should work.
> 
> > Might be better to just insert 6 bytes of padding with a comment, but yes I
> > agree that it's probably better to align it to at least machine word size.
> 
> Padding is fragile, e.g. if struct rcu_head changes. Using __aligned should
> make it always right automatically.
> 
> A.

I agree that __aligned is better.  It should work; see 'struct crypto_tfm' in
include/linux/crypto.h for another example of a struct that uses __aligned on a
flexible array at the end.

Aaro, can you send a formal patch?  If you don't I'll do so, but I figure I'll
ask first.

Thanks,

- Eric

  reply	other threads:[~2019-01-10 23:01 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-12-30 16:29 Bug report: unaligned access with ext4 encryption Aaro Koskinen
2019-01-03 17:17 ` Eric Biggers
2019-01-04 17:28 ` David Howells
2019-01-10 22:29   ` Aaro Koskinen
2019-01-10 23:01     ` Eric Biggers [this message]
2019-01-10 23:35       ` Aaro Koskinen

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