linux-kernel - Re: [PATCH v2 2/8] mm: Add kvmalloc_ab_c and kvzalloc

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Date:   Wed, 14 Feb 2018 12:45:52 -0800
From:   Joe Perches <joe@...ches.com>
To:     Matthew Wilcox <willy@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     Matthew Wilcox <mawilcox@...rosoft.com>, linux-mm@...ck.org,
        Kees Cook <keescook@...omium.org>,
        linux-kernel@...r.kernel.org, kernel-hardening@...ts.openwall.com
Subject: Re: [PATCH v2 2/8] mm: Add kvmalloc_ab_c and kvzalloc_struct

On Wed, 2018-02-14 at 12:11 -0800, Matthew Wilcox wrote:
> From: Matthew Wilcox <mawilcox@...rosoft.com>
> 
> We have kvmalloc_array in order to safely allocate an array with a
> number of elements specified by userspace (avoiding arithmetic overflow
> leading to a buffer overrun).  But it's fairly common to have a header
> in front of that array (eg specifying the length of the array), so we
> need a helper function for that situation.
> 
> kvmalloc_ab_c() is the workhorse that does the calculation, but in spite
> of our best efforts to name the arguments, it's really hard to remember
> which order to put the arguments in.  kvzalloc_struct() eliminates that
> effort; you tell it about the struct you're allocating, and it puts the
> arguments in the right order for you (and checks that the arguments
> you've given are at least plausible).
> 
> For comparison between the three schemes:
> 
> 	sev = kvzalloc(sizeof(*sev) + sizeof(struct v4l2_kevent) * elems,
> 			GFP_KERNEL);
> 	sev = kvzalloc_ab_c(elems, sizeof(struct v4l2_kevent), sizeof(*sev),
> 			GFP_KERNEL);
> 	sev = kvzalloc_struct(sev, events, elems, GFP_KERNEL);

Perhaps kv[zm]alloc_buf_and_array is better naming.