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Re: [PATCH] ipc/sem: Avoid indexing past end of sem_array

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  Re: [PATCH] ipc/sem: Avoid indexing past end of sem_array Manfred Spraul <manfred@colorfullife.com> - 2017-05-14 16:00 +0200
    Re: [PATCH] ipc/sem: Avoid indexing past end of sem_array Kees Cook <keescook@chromium.org> - 2017-05-15 19:50 +0200

#1641091 — Re: [PATCH] ipc/sem: Avoid indexing past end of sem_array

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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

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#1641934

On Sun, May 14, 2017 at 6:54 AM, Manfred Spraul
<manfred@colorfullife.com> wrote:
> 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.

I'll double check with your series, but I think your change makes
sense regardless (since it makes it very clear that there are
allocated sems after the struct due to the [0] entry).

>
> - 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?

I'll test your series with the randstruct series and see what falls out. :)

Thanks!

-Kees

-- 
Kees Cook
Pixel Security

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