Date: Sun, 11 Mar 2012 16:42:37 -0700 From: Linus Torvalds <torvalds@...ux-foundation.org> To: Djalal Harouni <tixxdz@...ndz.org> Cc: Oleg Nesterov <oleg@...hat.com>, linux-kernel@...r.kernel.org, kernel-hardening@...ts.openwall.com, Andrew Morton <akpm@...ux-foundation.org>, Al Viro <viro@...iv.linux.org.uk>, Alexey Dobriyan <adobriyan@...il.com>, "Eric W. Biederman" <ebiederm@...ssion.com>, Vasiliy Kulikov <segoon@...nwall.com>, Kees Cook <keescook@...omium.org>, Solar Designer <solar@...nwall.com>, WANG Cong <xiyou.wangcong@...il.com>, James Morris <james.l.morris@...cle.com>, linux-security-module@...r.kernel.org, linux-fsdevel@...r.kernel.org, Alan Cox <alan@...rguk.ukuu.org.uk>, Greg KH <gregkh@...uxfoundation.org>, Ingo Molnar <mingo@...e.hu>, Stephen Wilson <wilsons@...rt.ca>, "Jason A. Donenfeld" <Jason@...c4.com> Subject: Re: [PATCH 1/9] exec: add a global execve counter On Sun, Mar 11, 2012 at 4:32 PM, Djalal Harouni <tixxdz@...ndz.org> wrote: >> >> Just increment the mm_count for the thing, and hold a reference to it, >> and now you're all done. > Please Linus have you checked the: > [PATCH 9/9] proc: improve and clean up /proc/<pid>/mem protection > > That keeping the mm struct wont work, since it will eat memory and the > OOM-killer will kill some innocent processes, and the abuse can only be > catched by the VFS. That's the point. I made the mistake of using mm_users initially, but ysing mm_count - which is what I said to use (and what Oleg fixed things to in commit 6d08f2c71397) should *not* have that problem. It just keeps the 'struct mm_struct' itself around. > What's your opinion on it ? What's the advantage? You replace it with *another* allocation, and a 64-bit thing that is much less useful. The size of the patch also speaks for itself: fs/proc/base.c | 99 ++++++++++++++++++++++++++++++++++++++++++++------------ and it's more complex and uses more memory on average (the refcount thing is *free* for usual cases). I do agree that it would be nicer if mm_struct was a bit smaller, but at the same time, I really don't see the advantage of replacing it with another allocation entirely that makes the code just more complicated. Linus
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