From: Al Viro <viro-3bDd1+5oDREiFSDQTTA3OLVCufUGDwFn@public.gmane.org>
To: Vasily Kulikov <segoon-cxoSlKxDwOJWk0Htik3J/w@public.gmane.org>
Cc: "Eric W. Biederman"
<ebiederm-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org>,
Containers
<containers-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org>,
"Serge E. Hallyn"
<serge.hallyn-GeWIH/nMZzLQT0dZR+AlfA@public.gmane.org>,
linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
kernel-hardening-ZwoEplunGu1jrUoiu81ncdBPR1lH4CV8@public.gmane.org
Subject: Re: [PATCH/RFC] user_ns: fix missing limiting of user_ns counts
Date: Fri, 28 Dec 2012 19:21:52 +0000 [thread overview]
Message-ID: <20121228192152.GA4939@ZenIV.linux.org.uk> (raw)
In-Reply-To: <20121228190435.GA8690@cachalot>
On Fri, Dec 28, 2012 at 11:04:35PM +0400, Vasily Kulikov wrote:
> > I'm sorry, but this is not a solution. Kernel is not x86-only; there are
> > architectures with far bigger minimal stack frame size. E.g. on sparc64
> > every fucking stack frame is at least 176 bytes. So your 100 calls deep
> > call chain will happily overflow the damn stack all by itself - kernel
> > stack on sparc64 is 16Kb total, including struct thread_info living there.
>
> Understood. How to properly fix it then? Looks like there are quite
> many kernel structures which may reference other structures which
> indirectly reference each other via kref, IOW it is not user_ns specific
> issue. With unprivileged user_ns the way it should be freed must be
> somehow changed.
There are many damn good reasons why kref should *not* be used without
thinking. It's been oversold as easy solution to all refcounting problems;
it isn't one. Don't use it here.
WARNING: multiple messages have this Message-ID (diff)
From: Al Viro <viro@ZenIV.linux.org.uk>
To: Vasily Kulikov <segoon@openwall.com>
Cc: kernel-hardening@lists.openwall.com,
Containers <containers@lists.linux-foundation.org>,
"Serge E. Hallyn" <serge.hallyn@ubuntu.com>,
linux-kernel@vger.kernel.org,
"Eric W. Biederman" <ebiederm@xmission.com>
Subject: [kernel-hardening] Re: [PATCH/RFC] user_ns: fix missing limiting of user_ns counts
Date: Fri, 28 Dec 2012 19:21:52 +0000 [thread overview]
Message-ID: <20121228192152.GA4939@ZenIV.linux.org.uk> (raw)
In-Reply-To: <20121228190435.GA8690@cachalot>
On Fri, Dec 28, 2012 at 11:04:35PM +0400, Vasily Kulikov wrote:
> > I'm sorry, but this is not a solution. Kernel is not x86-only; there are
> > architectures with far bigger minimal stack frame size. E.g. on sparc64
> > every fucking stack frame is at least 176 bytes. So your 100 calls deep
> > call chain will happily overflow the damn stack all by itself - kernel
> > stack on sparc64 is 16Kb total, including struct thread_info living there.
>
> Understood. How to properly fix it then? Looks like there are quite
> many kernel structures which may reference other structures which
> indirectly reference each other via kref, IOW it is not user_ns specific
> issue. With unprivileged user_ns the way it should be freed must be
> somehow changed.
There are many damn good reasons why kref should *not* be used without
thinking. It's been oversold as easy solution to all refcounting problems;
it isn't one. Don't use it here.
WARNING: multiple messages have this Message-ID (diff)
From: Al Viro <viro@ZenIV.linux.org.uk>
To: Vasily Kulikov <segoon@openwall.com>
Cc: kernel-hardening@lists.openwall.com,
Containers <containers@lists.linux-foundation.org>,
"Serge E. Hallyn" <serge.hallyn@ubuntu.com>,
linux-kernel@vger.kernel.org,
"Eric W. Biederman" <ebiederm@xmission.com>
Subject: Re: [PATCH/RFC] user_ns: fix missing limiting of user_ns counts
Date: Fri, 28 Dec 2012 19:21:52 +0000 [thread overview]
Message-ID: <20121228192152.GA4939@ZenIV.linux.org.uk> (raw)
In-Reply-To: <20121228190435.GA8690@cachalot>
On Fri, Dec 28, 2012 at 11:04:35PM +0400, Vasily Kulikov wrote:
> > I'm sorry, but this is not a solution. Kernel is not x86-only; there are
> > architectures with far bigger minimal stack frame size. E.g. on sparc64
> > every fucking stack frame is at least 176 bytes. So your 100 calls deep
> > call chain will happily overflow the damn stack all by itself - kernel
> > stack on sparc64 is 16Kb total, including struct thread_info living there.
>
> Understood. How to properly fix it then? Looks like there are quite
> many kernel structures which may reference other structures which
> indirectly reference each other via kref, IOW it is not user_ns specific
> issue. With unprivileged user_ns the way it should be freed must be
> somehow changed.
There are many damn good reasons why kref should *not* be used without
thinking. It's been oversold as easy solution to all refcounting problems;
it isn't one. Don't use it here.
next prev parent reply other threads:[~2012-12-28 19:21 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-12-28 17:56 [PATCH/RFC] user_ns: fix missing limiting of user_ns counts Vasily Kulikov
2012-12-28 17:56 ` Vasily Kulikov
2012-12-28 17:56 ` [kernel-hardening] " Vasily Kulikov
2012-12-28 18:43 ` Al Viro
2012-12-28 18:43 ` Al Viro
2012-12-28 18:43 ` [kernel-hardening] " Al Viro
[not found] ` <20121228184334.GZ4939-3bDd1+5oDREiFSDQTTA3OLVCufUGDwFn@public.gmane.org>
2012-12-28 19:04 ` Vasily Kulikov
2012-12-28 19:04 ` Vasily Kulikov
2012-12-28 19:04 ` [kernel-hardening] " Vasily Kulikov
2012-12-28 19:21 ` Al Viro [this message]
2012-12-28 19:21 ` Al Viro
2012-12-28 19:21 ` [kernel-hardening] " Al Viro
2012-12-29 4:05 ` Eric W. Biederman
2012-12-29 4:05 ` Eric W. Biederman
2012-12-29 4:05 ` [kernel-hardening] " Eric W. Biederman
2012-12-29 5:13 ` Al Viro
2012-12-29 5:13 ` Al Viro
[not found] ` <87wqw15wqb.fsf-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org>
2012-12-29 5:13 ` Al Viro
2012-12-29 5:22 ` Vasily Kulikov
2012-12-29 5:22 ` Vasily Kulikov
2012-12-29 5:22 ` [kernel-hardening] " Vasily Kulikov
2012-12-30 11:00 ` Vasily Kulikov
2012-12-30 11:00 ` Vasily Kulikov
2012-12-30 11:00 ` [kernel-hardening] " Vasily Kulikov
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