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From: Andrew Lutomirski <luto@mit.edu>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Will Drewry <wad@chromium.org>,
	linux-kernel@vger.kernel.org, keescook@chromium.org,
	john.johansen@canonical.com, serge.hallyn@canonical.com,
	coreyb@linux.vnet.ibm.com, pmoore@redhat.com, eparis@redhat.com,
	djm@mindrot.org, segoon@openwall.com, rostedt@goodmis.org,
	jmorris@namei.org, scarybeasts@gmail.com, avi@redhat.com,
	penberg@cs.helsinki.fi, viro@zeniv.linux.org.uk, mingo@elte.hu,
	akpm@linux-foundation.org, khilman@ti.com,
	borislav.petkov@amd.com, amwang@redhat.com, oleg@redhat.com,
	ak@linux.intel.com, eric.dumazet@gmail.com, gregkh@suse.de,
	dhowells@redhat.com, daniel.lezcano@free.fr,
	linux-fsdevel@vger.kernel.org,
	linux-security-module@vger.kernel.org, olofj@chromium.org,
	mhalcrow@google.com, dlaor@redhat.com, corbet@lwn.net,
	alan@lxorguk.ukuu.org.uk
Subject: Re: [PATCH PLACEHOLDER 1/3] fs/exec: "always_unprivileged" patch
Date: Thu, 12 Jan 2012 17:11:39 -0800	[thread overview]
Message-ID: <CAObL_7F8aYPDQ1xTFjOxWgoZfrtGNFVgMe2Ld61_=D+YY427qA@mail.gmail.com> (raw)
In-Reply-To: <CA+55aFzzRNHfSo-1DyzsAwYvj1Da-vyhMQP-OdrA-rWywsebcg@mail.gmail.com>

On Thu, Jan 12, 2012 at 4:57 PM, Linus Torvalds
<torvalds@linux-foundation.org> wrote:
> On Thu, Jan 12, 2012 at 4:42 PM, Andrew Lutomirski <luto@mit.edu> wrote:
>>
>> That may prevent another use: set this new flag, chroot, drop
>> privileges, accept network connections.  (The idea being that chroot
>> might work unprivileged if this flag is set.)
>
> Well, if you have privileges, then just do
>
>   chroot();
>   drop privileges
>
> and if you depend on the new flag, then you do
>
>   drop privileges
>   set new flag
>   chroot
>
> and if you want to work either way then you just do
>
>   error = chroot
>   drop privileges
>   set new flag
>   if error
>      chroot
>
> which does the right thing regardless of whether you had privileges
> and/or a new kernel or not.
>
> In any of the three cases I don't see why you'd ever want to drop
> privileges *after* setting the new flag.

Hmm...

What if you're a daemon that needs something like CAP_NET_BIND but
also wants to be able to run other helpers without CAP_NET_BIND?

(Also, preventing dropping of privileges will probably make a patch
more complicted -- I'll have to find and update all the places that
allow dropping privileges.)

--Andy

WARNING: multiple messages have this Message-ID (diff)
From: Andrew Lutomirski <luto@mit.edu>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Will Drewry <wad@chromium.org>,
	linux-kernel@vger.kernel.org, keescook@chromium.org,
	john.johansen@canonical.com, serge.hallyn@canonical.com,
	coreyb@linux.vnet.ibm.com, pmoore@redhat.com, eparis@redhat.com,
	djm@mindrot.org, segoon@openwall.com, rostedt@goodmis.org,
	jmorris@namei.org, scarybeasts@gmail.com, avi@redhat.com,
	penberg@cs.helsinki.fi, viro@zeniv.linux.org.uk, mingo@elte.hu,
	akpm@linux-foundation.org, khilman@ti.com,
	borislav.petkov@amd.com, amwang@redhat.com, oleg@redhat.com,
	ak@linux.intel.com, eric.dumazet@gmail.com, gregkh@suse.de,
	dhowells@redhat.com, daniel.lezcano@free.fr,
	linux-fsdevel@vger.kernel.org,
	linux-security-module@vger.kernel.org, olofj@chromium.org,
	mhalcrow@google.com, dlaor@redhat.com, corbet@lwn.net,
	alan@lxorguk.ukuu.org.uk
Subject: Re: [PATCH PLACEHOLDER 1/3] fs/exec: "always_unprivileged" patch
Date: Thu, 12 Jan 2012 17:11:39 -0800	[thread overview]
Message-ID: <CAObL_7F8aYPDQ1xTFjOxWgoZfrtGNFVgMe2Ld61_=D+YY427qA@mail.gmail.com> (raw)
In-Reply-To: <CA+55aFzzRNHfSo-1DyzsAwYvj1Da-vyhMQP-OdrA-rWywsebcg@mail.gmail.com>

On Thu, Jan 12, 2012 at 4:57 PM, Linus Torvalds
<torvalds@linux-foundation.org> wrote:
> On Thu, Jan 12, 2012 at 4:42 PM, Andrew Lutomirski <luto@mit.edu> wrote:
>>
>> That may prevent another use: set this new flag, chroot, drop
>> privileges, accept network connections.  (The idea being that chroot
>> might work unprivileged if this flag is set.)
>
> Well, if you have privileges, then just do
>
>   chroot();
>   drop privileges
>
> and if you depend on the new flag, then you do
>
>   drop privileges
>   set new flag
>   chroot
>
> and if you want to work either way then you just do
>
>   error = chroot
>   drop privileges
>   set new flag
>   if error
>      chroot
>
> which does the right thing regardless of whether you had privileges
> and/or a new kernel or not.
>
> In any of the three cases I don't see why you'd ever want to drop
> privileges *after* setting the new flag.

Hmm...

What if you're a daemon that needs something like CAP_NET_BIND but
also wants to be able to run other helpers without CAP_NET_BIND?

(Also, preventing dropping of privileges will probably make a patch
more complicted -- I'll have to find and update all the places that
allow dropping privileges.)

--Andy
--
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  reply	other threads:[~2012-01-13  1:12 UTC|newest]

Thread overview: 47+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2012-01-12 23:38 [PATCH PLACEHOLDER 1/3] fs/exec: "always_unprivileged" patch Will Drewry
2012-01-12 23:38 ` [PATCH v3 2/3] seccomp_filters: system call filtering using BPF Will Drewry
2012-01-13  0:51   ` Randy Dunlap
2012-01-12 23:59     ` Will Drewry
2012-01-12 23:59       ` Will Drewry
2012-01-13  1:35       ` Randy Dunlap
2012-01-13 17:39   ` Eric Paris
2012-01-13 18:50     ` Will Drewry
2012-01-13 18:50       ` Will Drewry
2012-01-12 23:38 ` [PATCH v3 3/3] Documentation: prctl/seccomp_filter Will Drewry
2012-01-15  1:52   ` Randy Dunlap
2012-01-16  1:41     ` Will Drewry
2012-01-17 23:29   ` Eric Paris
2012-01-17 23:29     ` Eric Paris
2012-01-17 23:54     ` Will Drewry
2012-01-12 23:47 ` [PATCH PLACEHOLDER 1/3] fs/exec: "always_unprivileged" patch Linus Torvalds
2012-01-13  0:03   ` Will Drewry
2012-01-13  0:42   ` Andrew Lutomirski
2012-01-13  0:57     ` Linus Torvalds
2012-01-13  0:57       ` Linus Torvalds
2012-01-13  1:11       ` Andrew Lutomirski [this message]
2012-01-13  1:11         ` Andrew Lutomirski
2012-01-13  1:17         ` Linus Torvalds
2012-01-14 13:30           ` Jamie Lokier
2012-01-14 19:21             ` Will Drewry
2012-01-14 19:21               ` Will Drewry
2012-01-14 20:22             ` Linus Torvalds
2012-01-14 21:04               ` Andrew Lutomirski
2012-01-15 20:16               ` Casey Schaufler
2012-01-15 20:59                 ` Andrew Lutomirski
2012-01-15 21:32                   ` Casey Schaufler
2012-01-15 21:32                     ` Casey Schaufler
2012-01-15 22:07                     ` Andrew Lutomirski
2012-01-16  2:04                       ` Will Drewry
2012-01-16  2:04                         ` Will Drewry
2012-01-18  3:12                         ` Eric W. Biederman
2012-01-18  3:12                           ` Eric W. Biederman
2012-01-16  2:41                       ` Casey Schaufler
2012-01-16  2:41                         ` Casey Schaufler
2012-01-16  7:45                         ` Andrew Lutomirski
2012-01-16 18:02                           ` Casey Schaufler
2012-01-16 18:02                             ` Casey Schaufler
2012-01-13  1:37         ` Will Drewry
2012-01-13  1:41           ` Andrew Lutomirski
2012-01-13  1:41             ` Andrew Lutomirski
2012-01-13  2:09             ` Kees Cook
2012-01-13  2:09               ` Kees Cook

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