linux-kernel - Re: regarding mprotect() implementation in 2.6.26 kernel

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Message-ID: <4891D58E.1070308@goop.org>
Date:	Thu, 31 Jul 2008 08:09:02 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Maxin John <maxin.john@...il.com>
CC:	linux-kernel@...r.kernel.org
Subject: Re: regarding mprotect() implementation in 2.6.26 kernel

Maxin John wrote:
> Dear Christoph Hellwig,
>
> ( I guess you are the right person to ask this question ?)
>
> The POSIX.2 specification of mprotect() says:
>
> errorno should be set as ENOMEM if the addresses in the range [addr,
> (addr + len)] are invalid for the address space of a process, or
> specify one or more pages which are not mapped.
>
> However, in the mprotect implementation  (asmlinkage long
> sys_mprotect(unsigned long start, size_t len, unsigned long prot)) in
> linux/mm/mprotect.c file, if we call mprotect() with start as NULL and
> len as 0, mprotect() returns 0 and it is not setting the errono.The
> following code confirms this behaviour.
>   

Address 0 is a valid process address.  And you've set the length to
zero, so you technically haven't referred to any memory at all, so it
doesn't matter what the address is.

    J
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