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From: NeilBrown <neilb@suse.de>
To: Vasiliy Kulikov <segoon@openwall.com>
Cc: kernel-hardening@lists.openwall.com,
	Solar Designer <solar@openwall.com>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Stephen Smalley <sds@tycho.nsa.gov>,
	James Morris <jmorris@namei.org>,
	linux-kernel@vger.kernel.org, Greg Kroah-Hartman <gregkh@suse.de>,
	Andrew Morton <akpm@linux-foundation.org>,
	"David S. Miller" <davem@davemloft.net>,
	Jiri Slaby <jslaby@suse.cz>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	linux-fsdevel@vger.kernel.org,
	KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
	Eric Paris <eparis@redhat.com>, Willy Tarreau <w@1wt.eu>,
	Sebastian Krahmer <krahmer@suse.de>
Subject: Re: [patch v2] move RLIMIT_NPROC check from set_user() to do_execve_common()
Date: Wed, 27 Jul 2011 12:15:49 +1000	[thread overview]
Message-ID: <20110727121549.67a84d18@notabene.brown> (raw)
In-Reply-To: <20110726144848.GA7133@albatros>

On Tue, 26 Jul 2011 18:48:48 +0400 Vasiliy Kulikov <segoon@openwall.com>
wrote:

> Neil, Solar,
> 
> On Tue, Jul 26, 2011 at 14:11 +1000, NeilBrown wrote:
> > I don't really see that failing mmap is any more hackish than failing execve.
> > 
> > Both are certainly hacks.  It is setuid that should fail, but that is
> > problematic.
> > 
> > We seem to agree that it is acceptable to delay the failure until the process
> > actually tries to run some code for the user.  I just think that
> > mapping-a-file-for-exec is a more direct measure of "trying to run some code
> > for the user" than "execve" is.
> > 
> > So they are both hacks, but one it more thorough than the other.  In the
> > world of security I would hope that "thorough" would win.
> 
> Well, I don't mind against something more generic than the check in
> execve(), however, the usefulness of the check in mmap() is unclear to
> me.  You want to make more programs fail after setuid(), but does mmap
> stops really many programs?  Do you know any program doing mmap/dlopen
> after setuid() call?  What if the program will not do any mmap/dlopen
> and e.g. start to handle network connections or do some computations?
> I suppose the latter case is much more often than mmap/dlopen.

I think I didn't make myself clear.
I don't mean we should intercept the mmap system call.

I mean we could intercept the internal kernel function do_mmap_pgoff.

This is used by the mmap system call but also (and more importantly) by the
execve system call and the uselib system call.

So any attempt to map a file and execute the code in that file - whether via
exec or via mapping a shared object - will go through do_mmap_pgoff.

So if we disable do_mmap_pgoff() requests which ask for execute permission
when a setuid has caused RLIMIT_NPROC to be exceeded, then we catch every
attempt to run the user's code as the user.

I won't catch a situation where an interpreter is already loaded into the
root-owned process and the setuid is followed by loading a script and running
that, it is isn't perfect.  But I think it is more general than just trapping
in execve.

NeilBrown


  reply	other threads:[~2011-07-27  2:16 UTC|newest]

Thread overview: 35+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <20110612130953.GA3709@albatros>
     [not found] ` <20110706173631.GA5431@albatros>
     [not found]   ` <CA+55aFyfjG1h2zkkGai_VPM8p5bhWhvNXs1HvuWMgxv4RSywYw@mail.gmail.com>
     [not found]     ` <20110706185932.GB3299@albatros>
     [not found]       ` <20110707075610.GA3411@albatros>
     [not found]         ` <20110707081930.GA4393@albatros>
2011-07-12 13:27           ` [PATCH] move RLIMIT_NPROC check from set_user() to do_execve_common() Vasiliy Kulikov
2011-07-12 21:16             ` Linus Torvalds
2011-07-12 23:14               ` NeilBrown
2011-07-13  6:31                 ` Solar Designer
2011-07-13  7:06                   ` NeilBrown
2011-07-13 20:46                     ` Linus Torvalds
2011-07-14  0:11                       ` James Morris
2011-07-14  1:27                         ` NeilBrown
2011-07-14 15:06                           ` Solar Designer
2011-07-15  3:30                             ` NeilBrown
2011-07-15  5:35                               ` Willy Tarreau
2011-07-15  6:31                               ` [kernel-hardening] " Vasiliy Kulikov
2011-07-15  7:06                                 ` NeilBrown
2011-07-15  7:38                                   ` Vasiliy Kulikov
2011-07-15 13:04                                     ` Solar Designer
2011-07-15 13:58                                     ` [kernel-hardening] " Stephen Smalley
2011-07-15 15:26                                       ` Vasiliy Kulikov
2011-07-15 19:54                                         ` Stephen Smalley
2011-07-21  4:09                                           ` NeilBrown
2011-07-21 12:48                                             ` Solar Designer
2011-07-21 18:21                                               ` Linus Torvalds
2011-07-21 19:39                                                 ` [kernel-hardening] " Solar Designer
2011-07-25 17:14                                                   ` Vasiliy Kulikov
2011-07-25 23:40                                                     ` [kernel-hardening] " Solar Designer
2011-07-26  0:47                                                       ` NeilBrown
2011-07-26  1:16                                                         ` Solar Designer
2011-07-26  4:11                                                           ` NeilBrown
2011-07-26 14:48                                                             ` [patch v2] " Vasiliy Kulikov
2011-07-27  2:15                                                               ` NeilBrown [this message]
2011-07-29  7:07                                                                 ` [kernel-hardening] " Vasiliy Kulikov
2011-07-29  8:06                                                               ` Vasiliy Kulikov
2011-07-29  8:11                                                                 ` [patch v3] " Vasiliy Kulikov
2011-07-29  8:17                                                                   ` James Morris
2011-07-14  1:30                         ` [PATCH] " KOSAKI Motohiro
2011-07-13  5:36             ` KOSAKI Motohiro

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