linux-kernel - Re: [uml-devel] [PATCH 1/1] hostfs: fix UML crash

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Date:	Mon, 18 Oct 2010 21:22:31 +0200
From:	Geert Uytterhoeven <geert@...ux-m68k.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Richard Weinberger <richard@....at>, toralf.foerster@....de,
	jdike@...toit.com, linux-kernel@...r.kernel.org,
	user-mode-linux-devel@...ts.sourceforge.net,
	viro@...iv.linux.org.uk
Subject: Re: [uml-devel] [PATCH 1/1] hostfs: fix UML crash

On Mon, Oct 18, 2010 at 20:40, Andrew Morton <akpm@...ux-foundation.org> wrote:
> On Mon, 18 Oct 2010 18:36:54 +0200 Richard Weinberger <richard@....at> wrote:
>> 365b1818 resized f_spare within struct statfs.
>> hostfs accesses f_spare directly and needs an update.
>>
>> Signed-off-by: Richard Weinberger <richard@....at>
>> Reported-by: Toralf F__rster <toralf.foerster@....de>
>> Tested-by: Toralf F__rster <toralf.foerster@....de>
>> ---
>>  fs/hostfs/hostfs_user.c |    2 +-
>>  1 files changed, 1 insertions(+), 1 deletions(-)
>>
>> diff --git a/fs/hostfs/hostfs_user.c b/fs/hostfs/hostfs_user.c
>> index 6777aa0..ce2f168 100644
>> --- a/fs/hostfs/hostfs_user.c
>> +++ b/fs/hostfs/hostfs_user.c
>> @@ -388,6 +388,6 @@ int do_statfs(char *root, long *bsize_out, long long *blocks_out,
>>       spare_out[1] = buf.f_spare[1];
>>       spare_out[2] = buf.f_spare[2];
>>       spare_out[3] = buf.f_spare[3];
>> -     spare_out[4] = buf.f_spare[4];
>> +
>>       return 0;
>>  }
>
> Thanks.
>
> Is there any reason for hostfs to be playing with the f_spare field at all?

It just copies it from struct statfs64 on the host to struct kstatfs
on the guest.
Probably a memcpy() is more future-safe, if it's combined with a
BUILD_BUG_ON(sizeof(statfs64.f_spare) != sizeof(kstatfs.f_spare)).

Still, currently it doesn't copy the recently added f_flags field.
To protect against future changes like that, an explicit
BUILD_BUG_ON(sizeof(kstatfs.f_spare) != 4*sizeof(long)) may be even
better...

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds
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