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Date: Thu, 5 Oct 2017 18:33:20 +0200
From: Oleg Nesterov <oleg@redhat.com>
To: Michal Hocko <mhocko@kernel.org>
Cc: Baoquan He <bhe@redhat.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Kees Cook <keescook@chromium.org>, Jiri Kosina <jkosina@suse.cz>,
        Al Viro <viro@zeniv.linux.org.uk>, Ingo Molnar <mingo@elte.hu>,
        LKML <linux-kernel@vger.kernel.org>
Subject: Re: MAP_FIXED for ELF mappings
Message-ID: <20171005163320.GA20848@redhat.com>
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On 10/04, Michal Hocko wrote:
>
> On Wed 04-10-17 23:12:38, Baoquan He wrote:
> >  	if (total_size) {
> >  		total_size = ELF_PAGEALIGN(total_size);
> > -		map_addr = vm_mmap(filep, addr, total_size, prot, flags, off);
> > -		if (!BAD_ADDR(map_addr))
> > -			vm_munmap(map_addr+size, total_size-size);
> > -	} else
> > -		map_addr = vm_mmap(filep, addr, size, prot, flags, off);
> > +		addr = get_unmapped_area(file, addr, total_size, off, flags);
>
> So how does this prevent clobbering an existing VMA when flags contains
> MAP_FIXED?

I got lost...

this is just cleanup, it should not change the behaviour, with or without
MAP_FIXED. It just avoids the mmap(total_size) + munmap(extra_size).

Oleg.