Date: Thu, 31 May 2018 21:18:10 -0700 From: Kees Cook <keescook@...omium.org> To: Linus Torvalds <torvalds@...ux-foundation.org> Cc: Matthew Wilcox <mawilcox@...rosoft.com>, Rasmus Villemoes <linux@...musvillemoes.dk>, Matthew Wilcox <willy@...radead.org>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, linux-mm <linux-mm@...ck.org>, Kernel Hardening <kernel-hardening@...ts.openwall.com> Subject: Re: [PATCH v3 00/16] Provide saturating helpers for allocation On Thu, May 31, 2018 at 5:54 PM, Linus Torvalds <torvalds@...ux-foundation.org> wrote: > On Thu, May 31, 2018 at 7:43 PM Kees Cook <keescook@...omium.org> wrote: >> >> So, while nothing does: >> kmalloc_array(a, b, ...) -> kmalloc(array_size(a, b), ...) >> the treewide changes DO perform changes like this: >> kmalloc(a * b, ...) -> kmalloc(array_size(a, b), ...) > > Ugh. I really really still absolutely despise this. Heh. Yeah, I called this out specifically because I wasn't sure if this was going to be okay. :P > Why can't you just have a separate set of coccinelle scripts that do > the simple and clean cases? > > So *before* doing any array_size() conversions, just do > > kzalloc(a*b, ...) -> kcalloc(a, b, ...) > kmalloc(a*b,..) -> kmalloc_array(a,b, ...) > > and the obvious variations on that (devm_xyz() has all the same helpers). Yup. I'll get started on it. I did have a version of a python script that generated coccinelle scripts, but I started losing my mind. I'll double-check if I can find a way to do some internal-to-Coccinelle python to handle some of the variation directly, etc. For those interested in the details: the complexity for me is in how Coccinelle handles expressions (or my understanding of it's handling). There's nothing in between "expression" and "identifier", so "thing->field" is an expression not an identifier ("thing" is an identifier), but "foo * bar" is _also_ an expression, so I have to slowly peel away the "easy" stuff (sizeof, constants, etc) before expressions to avoid collapsing factors into the wrong arguments (e.g. kzalloc(a * b * c, ...) -> kcalloc(a * b, c, ...) is not desirable), so there end up being a LOT of rules... I was able to compress allocation families into a a regex, but without that, I'll end up with the sizeof/const/etc rules times the family times the kalloc and _array rules. > Only after doing the ones that don't have the nice obvious helpers, do > the remaining ones with array_size(), ie > > *alloc(a*b, ..) -> *alloc(array_size(a,b), ...) > > because that really makes for much less legible code. > > Hmm? Sounds good. Thanks! -Kees -- Kees Cook Pixel Security
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