From: ebiederm@xmission.com (Eric W. Biederman)
To: Kees Cook <keescook@chromium.org>
Cc: Oleg Nesterov <oleg@redhat.com>,
David Howells <dhowells@redhat.com>,
linux-kernel@vger.kernel.org,
Andrew Morton <akpm@linux-foundation.org>,
Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@kernel.org>,
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
Rik van Riel <riel@redhat.com>,
Vladimir Davydov <vdavydov@parallels.com>,
Ricky Zhou <rickyz@chromium.org>, Julien Tinnes <jln@google.com>
Subject: Re: [PATCH] user_ns: use correct check for single-threadedness
Date: Tue, 28 Jul 2015 13:17:40 -0500 [thread overview]
Message-ID: <87d1zcm9iz.fsf@x220.int.ebiederm.org> (raw)
In-Reply-To: <20150728171500.GA2871@www.outflux.net> (Kees Cook's message of "Tue, 28 Jul 2015 10:15:00 -0700")
Kees Cook <keescook@chromium.org> writes:
> From: Ricky Zhou <rickyz@chromium.org>
>
> Checking mm_users > 1 does not mean a process is multithreaded. For
> example, reading /proc/PID/maps temporarily increments mm_users, allowing
> other processes to (accidentally) interfere with unshare() calls.
>
> This fixes observed failures of unshare(CLONE_NEWUSER) incorrectly
> returning EINVAL if another processes happened to be simultaneously
> reading the maps file.
>
> Signed-off-by: Ricky Zhou <rickyz@chromium.org>
> Signed-off-by: Kees Cook <keescook@chromium.org>
> Cc: stable@vger.kernel.org
This looks like a good fix. Any chance you can drudge up the commit where
this hack came in so that Greg & Company know how far to back port this?
> ---
> kernel/fork.c | 4 ++--
> kernel/user_namespace.c | 3 ++-
> 2 files changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/kernel/fork.c b/kernel/fork.c
> index dbd9b8d7b7cc..7d138f152dcd 100644
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -75,6 +75,7 @@
> #include <linux/aio.h>
> #include <linux/compiler.h>
> #include <linux/sysctl.h>
> +#include <linux/sched.h>
>
> #include <asm/pgtable.h>
> #include <asm/pgalloc.h>
> @@ -1876,8 +1877,7 @@ static int check_unshare_flags(unsigned long unshare_flags)
> * needs to unshare vm.
> */
> if (unshare_flags & (CLONE_THREAD | CLONE_SIGHAND | CLONE_VM)) {
> - /* FIXME: get_task_mm() increments ->mm_users */
> - if (atomic_read(¤t->mm->mm_users) > 1)
> + if (!current_is_single_threaded())
> return -EINVAL;
> }
>
> diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
> index 4109f8320684..7e0e021e4304 100644
> --- a/kernel/user_namespace.c
> +++ b/kernel/user_namespace.c
> @@ -22,6 +22,7 @@
> #include <linux/ctype.h>
> #include <linux/projid.h>
> #include <linux/fs_struct.h>
> +#include <linux/sched.h>
>
> static struct kmem_cache *user_ns_cachep __read_mostly;
> static DEFINE_MUTEX(userns_state_mutex);
> @@ -977,7 +978,7 @@ static int userns_install(struct nsproxy *nsproxy, struct ns_common *ns)
> return -EINVAL;
>
> /* Threaded processes may not enter a different user namespace */
> - if (atomic_read(¤t->mm->mm_users) > 1)
> + if (!current_is_single_threaded())
> return -EINVAL;
>
> if (current->fs->users != 1)
> --
> 1.9.1
next prev parent reply other threads:[~2015-07-28 18:24 UTC|newest]
Thread overview: 41+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-07-28 17:15 [PATCH] user_ns: use correct check for single-threadedness Kees Cook
2015-07-28 18:02 ` Rik van Riel
2015-07-28 18:17 ` Eric W. Biederman [this message]
2015-07-28 20:55 ` Ricky Zhou
2015-07-28 21:01 ` Kees Cook
2015-08-05 18:13 ` Eric W. Biederman
2015-08-05 19:40 ` Kees Cook
2015-07-28 21:35 ` Andrew Morton
2015-07-28 21:50 ` Kees Cook
2015-07-28 22:11 ` Kirill A. Shutemov
2015-08-05 11:38 ` Ingo Molnar
2015-08-05 11:53 ` Kirill A. Shutemov
2015-08-05 13:13 ` Ricky Zhou
2015-08-05 17:23 ` Oleg Nesterov
2015-08-05 18:00 ` Eric W. Biederman
2015-08-05 18:52 ` Eric W. Biederman
2015-08-06 13:06 ` Oleg Nesterov
2015-08-06 13:44 ` Oleg Nesterov
2015-08-12 1:17 ` Eric W. Biederman
2015-08-12 14:40 ` Oleg Nesterov
2015-08-12 15:11 ` Eric W. Biederman
2015-08-12 1:22 ` [PATCH 0/2] userns: Creation logic fixes Eric W. Biederman
2015-08-12 1:24 ` [PATCH 1/2] unshare: Unsharing a thread does not require unsharing a vm Eric W. Biederman
2015-08-12 17:48 ` Oleg Nesterov
2015-08-12 18:39 ` Eric W. Biederman
2015-08-13 12:55 ` Oleg Nesterov
2015-08-13 15:38 ` Eric W. Biederman
2015-08-13 16:17 ` Oleg Nesterov
2015-08-13 16:27 ` Eric W. Biederman
2015-08-13 16:50 ` Oleg Nesterov
2015-08-14 17:59 ` Oleg Nesterov
2015-08-12 19:59 ` [PATCH v2] " Eric W. Biederman
2015-08-13 12:57 ` Oleg Nesterov
2015-08-13 16:01 ` Eric W. Biederman
2015-08-13 16:30 ` Oleg Nesterov
2015-08-13 16:39 ` Eric W. Biederman
2015-08-12 1:25 ` [PATCH 2/2] userns,pidns: Force thread group sharing, not signal handler sharing Eric W. Biederman
2015-08-12 17:24 ` Oleg Nesterov
2015-08-12 6:29 ` [PATCH 0/2] userns: Creation logic fixes Kees Cook
2015-08-06 14:35 ` [PATCH] user_ns: use correct check for single-threadedness Oleg Nesterov
2015-08-06 21:16 ` Eric W. Biederman
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