From: Ricky Zhou <rickyz@google.com>
To: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Kees Cook <keescook@chromium.org>,
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>,
Julien Tinnes <jln@google.com>
Subject: Re: [PATCH] user_ns: use correct check for single-threadedness
Date: Tue, 28 Jul 2015 13:55:40 -0700 [thread overview]
Message-ID: <CAJmxDmRZTF1BFG5p3KfCTuBLLWFNNzxtDyacWJp4S=mTW7Aoww@mail.gmail.com> (raw)
In-Reply-To: <87d1zcm9iz.fsf@x220.int.ebiederm.org>
(apologies for the dup, forgot to reply all)
userns_install in user_namespace.c (affects setns of a user
namespace): cde1975bc242f3e1072bde623ef378e547b73f91.
The check in check_unshare_flags is a little more complex. The
incorrect check was added in
cf2e340f4249b781b3d2beb41e891d08581f0e10 but I don't think it would
have triggered under any supported combination of flags at that point.
>From 50804fe3737ca6a5942fdc2057a18a8141d00141 until
6e556ce209b09528dbf1931cbfd5d323e1345926, the bug affected
unshare(CLONE_NEWPID).
>From b2e0d98705e60e45bbb3c0032c48824ad7ae0704 onward,
unshare(CLONE_NEWUSER) is affected.
Thanks,
Ricky
On Tue, Jul 28, 2015 at 11:17 AM, Eric W. Biederman
<ebiederm@xmission.com> wrote:
> 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 20:55 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
2015-07-28 20:55 ` Ricky Zhou [this message]
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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