linux-kernel - Re: [PATCH] asm-generic: uaccess: fix up local access

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Message-ID: <8bd0f97a0906131747odfe851chebfef9a541fa5c58@mail.gmail.com>
Date:	Sat, 13 Jun 2009 20:47:20 -0400
From:	Mike Frysinger <vapier.adi@...il.com>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] asm-generic: uaccess: fix up local access_ok() usage

On Sat, Jun 13, 2009 at 16:53, Arnd Bergmann wrote:
> On Saturday 13 June 2009, Mike Frysinger wrote:
>> There's no reason that I can see to use the short __access_ok() form
>> directly when the access_ok() is clearer in intent and for more people,
>> expands to the same C code (i.e. always specify the first field -- access
>> type).  Not all no-mmu systems lack memory protection, so the read/write
>> could feasibly be checked.
>
> Ah, I didn't consider this. I checked all the architectures and could not
> find a case where access_ok actually evaluates the the first argument, so
> I chose the slightly terser variant. I also don't let you override
> access_ok() at this moment, which means that you don't have a choice
> to use the generic uaccess.h and still differentiate between read and
> write accesses.

well, if you dont mind a bit of cruft, you can undef it ;)
#include <asm-generic/uaccess.h>
#undef access_ok

the Blackfin port does have hardware memory protection (MPU) and it
does handle r/w/x bits, but we havent merged this into access_ok yet,
just the vma lists

> What I really got wrong was the prototype for __access_ok(), as you
> showed in your follow-up. I only tested this with the microblaze
> patch that overrides __access_ok() with an architecture specific
> version that gets this part right.

yeah, that looks good, but i'd still like the __access_ok -> access_ok

>> Also, the strnlen_user() function was missing a access_ok() check on the
>> pointer given.  We've had cases on Blackfin systems where test cases
>> caused kernel crashes here because userspace passed up a NULL/-1 pointer
>> and the kernel gladly attempted to run strlen() on it.
>
> Right, well spotted. I'll take this fix as a separate patch, ok?

np
-mike
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