linux-kernel - Re: [PATCH] mmap.2: mmap with address NULL and MAP

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Message-ID: <20170616152546.GA31298@dhcp22.suse.cz>
Date:   Fri, 16 Jun 2017 17:25:47 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Theodore Dubois <tblodt@...oud.com>
Cc:     mtk.manpages@...il.com, linux-man@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mmap.2: mmap with address NULL and MAP_FIXED results in
 EPERM

On Thu 15-06-17 12:09:01, Theodore Dubois wrote:
> This can be verified with a simple test program. I'm not sure if this is
> a kernel bug or a documentation bug, though...

THis is not a bug. You are not allowed to mmap anything below
/proc/sys/vm/mmap_min_addr. So your patch to update documentation would
have to mention this sysctl to be correct.

> ---
>  man2/mmap.2 | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/man2/mmap.2 b/man2/mmap.2
> index d1942b52a..58361c837 100644
> --- a/man2/mmap.2
> +++ b/man2/mmap.2
> @@ -515,6 +515,13 @@ was mounted no-exec.
>  .\" (Since 2.4.25 / 2.6.0.)
>  .TP
>  .B EPERM
> +The
> +.I addr
> +argument is 0 and
> +.B MAP_FIXED
> +is specified.
> +.TP
> +.B EPERM
>  The operation was prevented by a file seal; see
>  .BR fcntl (2).
>  .TP
> -- 
> 2.13.1

-- 
Michal Hocko
SUSE Labs