linux-kernel - Re: flex_array related problems on selinux policy loading

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Date:	Wed, 26 Jan 2011 08:15:26 -0800
From:	Dave Hansen <dave@...ux.vnet.ibm.com>
To:	Steffen Klassert <steffen.klassert@...unet.com>
Cc:	Eric Paris <eparis@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-security-module@...r.kernel.org
Subject: Re: flex_array related problems on selinux policy loading

On Wed, 2011-01-26 at 14:04 +0100, Steffen Klassert wrote:
> Another thing came to my mind. An atempt to do a zero size allocation
> always succeed on kmalloc. If we want to allocate our metadata even in
> this case, we should be aware that this allocation _can_ fail. So
> flex_array_alloc would not show the same behaviour as kmalloc on zero
> size allocations.

I think that's just fine.

You have to check for and handle those allocation failures anyway.  Can
you think of places in the kernel where we have known-zero-sized
allocations that don't check kmalloc() returns?

> As most potential flex_array users convert their code
> from kmalloc, the behaviour of flex_array_alloc should be the same as of
> kmalloc. Showing a different behaviour here will produce pitfalls for
> potential new users. Also, to tell a user that we can not allocate memory
> for him, if the wants to allocate 0 byte (nothing) is quite odd. This
> user could easily continue processing, even if we can not allocate our
> metadata in this moment.

This doesn't have to be a one to one, direct, replacement for kmalloc().
As long as it's close enough not to confuse people or normally cause
problems, I think it's fine.
-- Dave

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