linux-kernel - Re: [PATCH -next v2 0/4] mm: replace mmap_sem for mm->exe

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Date:	Sun, 15 Mar 2015 10:34:23 -0700
From:	Davidlohr Bueso <dave@...olabs.net>
To:	Cyrill Gorcunov <gorcunov@...il.com>
Cc:	Oleg Nesterov <oleg@...hat.com>, akpm@...ux-foundation.org,
	viro@...iv.linux.org.uk, koct9i@...il.com, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, Kees Cook <keescook@...omium.org>,
	"Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>,
	Linux API <linux-api@...r.kernel.org>
Subject: Re: [PATCH -next v2 0/4] mm: replace mmap_sem for mm->exe_file
 serialization

On Sun, 2015-03-15 at 20:05 +0300, Cyrill Gorcunov wrote:
> On Sun, Mar 15, 2015 at 08:42:05AM -0700, Davidlohr Bueso wrote:
> > > > > Yes, this code needs cleanups, I agree. Does this series makes it better?
> > > > > To me it doesn't, and the diffstat below shows that it blows the code.
> > > >
> > > > Looking at some of the caller paths now, I have to disagree.
> > > 
> > > And I believe you are wrong. But let me repeat, I leave this to Cyrill
> > > and Konstantin. Cleanups are always subjective.
> > > 
> > > > > In fact, to me it complicates this code. For example. Personally I think
> > > > > that MMF_EXE_FILE_CHANGED should die. And currently we can just remove it.
> > > >
> > > > How could you remove this?
> > > 
> > > Just remove this flag and the test_and_set_bit(MMF_EXE_FILE_CHANGED) check.
> > > Again, this is subjective, but to me it looks ugly. Why do we allow to
> > > change ->exe_file but only once?
> 
> This came from very first versions of the functionality implemented
> in prctl. It supposed to help sysadmins to notice if there exe
> transition happened. As to me it doesn't bring much security, if I
> would be a virus I would simply replace executing code with ptrace
> or via other ways without telling outside world that i've changed
> exe path. That said I would happily rip off this MMF_EXE_FILE_CHANGED
> bit but I fear security guys won't be that happy about it.
> (CC'ing Kees)

Also adding Michael for any prctl manpage and api changes.

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