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Date:   Fri, 11 Jan 2019 00:29:28 +0200
From:   Aaro Koskinen <>
To:     David Howells <>
Cc:     Eric Biggers <>,
        "Theodore Y. Ts'o" <>,
        Jaegeuk Kim <>,,,
Subject: Re: Bug report: unaligned access with ext4 encryption


On Fri, Jan 04, 2019 at 05:28:02PM +0000, David Howells wrote:
> Eric Biggers <> 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.


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