linux-kernel - Re: [PATCH] fs/pipe: fix shift by 64 in F_SETPIPE

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Date:	Mon, 15 Aug 2016 10:55:34 +0200
From:	Vegard Nossum <vegard.nossum@...cle.com>
To:	Willy Tarreau <w@....eu>
Cc:	Al Viro <viro@...iv.linux.org.uk>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] fs/pipe: fix shift by 64 in F_SETPIPE_SZ

On 08/15/2016 10:34 AM, Willy Tarreau wrote:
> On Mon, Aug 15, 2016 at 10:22:38AM +0200, Vegard Nossum wrote:
>> In both cases I found it better to be more conservative in what we
>> accept, i.e. I haven't checked whether the rest of the code would
>> support pipe buffers > INT_MAX on 64-bit and I think it's a slightly
>> bigger job to check that (not just for the person making the change, but
>> for everybody else looking at/reviewing it) -- it's already tricky
>> enough to verify that this change by itself is safe and correct IMHO.
>
> Well in fact in my opinion it's the opposite, because if we ensure the
> function works well over all its argument type's range, the caller has
> less trouble figuring what sub-part of the range is OK. This is exactly
> the current issue where you have to ensure that :
>
>       unsigned int arg <= INT_MAX

It's not just about this one function, but all the other code in pipe.c
now has to cope with pipe buffers > INT_MAX as well.

For example all the fields in struct pipe_inode_info referring to
buffers are unsigned int (nrbufs, curbuf, buffers). Unless we also
change those to unsigned long, the code will definitely not support
buffer sizes up to LONG_MAX on 64-bit.

That's why I think it's a much, much bigger task to review (and make)
such a change.


Vegard