linux-kernel - Re: [PATCH] flex_array: Change behaviour on zero size allocations

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Message-ID: <20110201110311.GM3070@secunet.com>
Date:	Tue, 1 Feb 2011 12:03:11 +0100
From:	Steffen Klassert <steffen.klassert@...unet.com>
To:	Dave Hansen <dave@...ux.vnet.ibm.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Eric Paris <eparis@...hat.com>, linux-kernel@...r.kernel.org,
	linux-security-module@...r.kernel.org
Subject: Re: [PATCH] flex_array: Change behaviour on zero size allocations

On Tue, Feb 01, 2011 at 11:24:18AM +0100, Steffen Klassert wrote:
> 
> Both objections are correct, I'll send an updated patch.
> 

I think we need to fix selinux too to get rid of the policy loading
problem. In security/selinux/ss/policydb.c are several pieces of code
like this one:

p->type_val_to_struct_array = flex_array_alloc(sizeof(struct type_datum *),   
                                               p->p_types.nprim,              
                                               GFP_KERNEL | __GFP_ZERO);
if (!p->type_val_to_struct_array)      
	goto out;

rc = flex_array_prealloc(p->type_val_to_struct_array, 0,
                         p->p_types.nprim - 1, GFP_KERNEL | __GFP_ZERO);
if (rc)
	goto out;

If p->p_types.nprim is zero, we allocare with total_nr_elements equal
to zerro and then we try to prealloc with p->p_types.nprim - 1.
flex_array_prealloc interprets this as an unsigned int and fails,
because this is bigger than total_nr_elements, which is correct I think.

Thoughts?

Steffen
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