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

[Geert Uytterhoeven]

On Mon, Oct 18, 2010 at 20:40, Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote:
> On Mon, 18 Oct 2010 18:36:54 +0200 Richard Weinberger <richard@xxxxxx> wrote:
>> 365b1818 resized f_spare within struct statfs.
>> hostfs accesses f_spare directly and needs an update.
>>
>> Signed-off-by: Richard Weinberger <richard@xxxxxx>
>> Reported-by: Toralf F__rster <toralf.foerster@xxxxxx>
>> Tested-by: Toralf F__rster <toralf.foerster@xxxxxx>
>> ---
>> Âfs/hostfs/hostfs_user.c | Â Â2 +-
>> Â1 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,
>> Â Â Â spare_out[1] = buf.f_spare[1];
>> Â Â Â spare_out[2] = buf.f_spare[2];
>> Â Â Â spare_out[3] = buf.f_spare[3];
>> - Â Â spare_out[4] = buf.f_spare[4];
>> +
>> Â Â Â return 0;
>> Â}
>
> 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@xxxxxxxxxxxxxx

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.
             Â Â -- Linus Torvalds
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