linux-kernel - [PATCH] kernel/time: Add max_time

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Message-Id: <20200406171342.128733-1-dima@arista.com>
Date:   Mon,  6 Apr 2020 18:13:42 +0100
From:   Dmitry Safonov <dima@...sta.com>
To:     linux-kernel@...r.kernel.org
Cc:     Dmitry Safonov <0x7f454c46@...il.com>,
        Dmitry Safonov <dima@...sta.com>,
        "Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>,
        Adrian Reber <adrian@...as.de>,
        Andrey Vagin <avagin@...nvz.org>,
        Christian Brauner <christian.brauner@...ntu.com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        Containers <containers@...ts.linux-foundation.org>,
        Linux API <linux-api@...r.kernel.org>, stable@...nel.org
Subject: [PATCH] kernel/time: Add max_time_namespaces ucount

Introduce missing time namespaces limit per-userns.
Michael noticed that userns limit for number of time namespaces is
missing.

Furthermore, time namespace introduced UCOUNT_TIME_NAMESPACES, but
didn't introduce an array member in user_table[]. It would make array's
initialisation OOB write, but by luck the user_table array has
an excessive empty member (all accesses to the array are limited with
UCOUNT_COUNTS - so it silently reuses the last free member.

Fixes user-visible regression: max_inotify_instances by reason of the
missing UCOUNT_ENTRY() has limited max number of namespaces instead of
the number of inotify instances.

Fixes: 769071ac9f20 ("ns: Introduce Time Namespace")
Cc: Adrian Reber <adrian@...as.de>
Cc: Andrey Vagin <avagin@...nvz.org>
Cc: Christian Brauner <christian.brauner@...ntu.com>
Cc: Eric W. Biederman <ebiederm@...ssion.com>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Vincenzo Frascino <vincenzo.frascino@....com>
Cc: Containers <containers@...ts.linux-foundation.org>
Cc: Linux API <linux-api@...r.kernel.org>
Cc: stable@...nel.org # v5.6+
Reported-by: Michael Kerrisk (man-pages) <mtk.manpages@...il.com>
Signed-off-by: Dmitry Safonov <dima@...sta.com>
---
 Documentation/admin-guide/sysctl/user.rst | 6 ++++++
 kernel/ucount.c                           | 1 +
 2 files changed, 7 insertions(+)

diff --git a/Documentation/admin-guide/sysctl/user.rst b/Documentation/admin-guide/sysctl/user.rst
index 650eaa03f15e..c45824589339 100644
--- a/Documentation/admin-guide/sysctl/user.rst
+++ b/Documentation/admin-guide/sysctl/user.rst
@@ -65,6 +65,12 @@ max_pid_namespaces
   The maximum number of pid namespaces that any user in the current
   user namespace may create.
 
+max_time_namespaces
+===================
+
+  The maximum number of time namespaces that any user in the current
+  user namespace may create.
+
 max_user_namespaces
 ===================
 
diff --git a/kernel/ucount.c b/kernel/ucount.c
index a53cc2b4179c..29c60eb4ec9b 100644
--- a/kernel/ucount.c
+++ b/kernel/ucount.c
@@ -69,6 +69,7 @@ static struct ctl_table user_table[] = {
 	UCOUNT_ENTRY("max_net_namespaces"),
 	UCOUNT_ENTRY("max_mnt_namespaces"),
 	UCOUNT_ENTRY("max_cgroup_namespaces"),
+	UCOUNT_ENTRY("max_time_namespaces"),
 #ifdef CONFIG_INOTIFY_USER
 	UCOUNT_ENTRY("max_inotify_instances"),
 	UCOUNT_ENTRY("max_inotify_watches"),
-- 
2.26.0