linux-kernel - Re: [PATCH] ipc/sem: Avoid indexing past end of sem

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Message-ID: <e5e0fa5c-cc26-d05d-a2d3-3a10d191cc70@colorfullife.com>
Date:   Sun, 14 May 2017 15:54:00 +0200
From:   Manfred Spraul <manfred@...orfullife.com>
To:     Kees Cook <keescook@...omium.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     Davidlohr Bueso <dave@...olabs.net>,
        Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Fabian Frederick <fabf@...net.be>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ipc/sem: Avoid indexing past end of sem_array

Hi Kees,

On 05/09/2017 12:23 AM, Kees Cook wrote:
> This changes the struct + trailing data pattern to using a void * so that
> the end of sem_array is found without possibly indexing past the end which
> can upset some static analyzers. Mostly, this ends up avoiding a cast
> between different non-void types, which the future randstruct GCC plugin
> was warning about.
Two question:
- Would the attached patch work with the randstruct plugin as well?
   If we touch the code, then I would propose that we remove sem_base 
entirely.

- ipc/util.h contains

 > #define ipc_rcu_to_struct(p)  ((void *)(p+1))

Does this trigger a warning with randstruct as well?
If we have to touch it, then I would remove it by merging struct 
kern_ipc_perm and struct ipc_rcu.

And, obviously:
Do you see any issues with the attached patch?
--
     Manfred

View attachment "0001-ipc-sem.c-remove-sem_base-embed-struct-sem.patch" of type "text/x-patch" (12759 bytes)