linux-hardening - Re: [PATCH] mm: Handle ksize() vs __alloc

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Message-Id: <20220225154518.0d1159fdc6f37ee38e39e90c@linux-foundation.org>
Date:   Fri, 25 Feb 2022 15:45:18 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Kees Cook <keescook@...omium.org>
Cc:     llvm@...ts.linux.dev, Marco Elver <elver@...gle.com>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Vlastimil Babka <vbabka@...e.cz>, linux-mm@...ck.org,
        stable@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Christoph Lameter <cl@...ux.com>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Daniel Micay <danielmicay@...il.com>,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH] mm: Handle ksize() vs __alloc_size by forgetting size

On Fri, 25 Feb 2022 14:16:25 -0800 Kees Cook <keescook@...omium.org> wrote:

> If ksize() is used on an allocation, the compiler cannot make any
> assumptions about its size any more (as hinted by __alloc_size). Force
> it to forget.
> 
> One caller was using a container_of() construction that needed to be
> worked around.

Please, when fixing something do fully explain what that thing is.  I,
for one, simply cannot understand why this change is being proposed.

Especially when proposing a -stable backport!  Tell readers what was
the end-user impact of the bug.

> Link: https://github.com/ClangBuiltLinux/linux/issues/1599

Even that didn't tell me.  Is it just a clang warning?  Does the kernel
post your private keys on reddit then scribble all over your disk
drive?  I dunno.