linux-kernel - [PATCH v2 06/10] utsns: Add a limit on the number of uts namespaces

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Message-Id: <20160721164014.17534-6-ebiederm@xmission.com>
Date:	Thu, 21 Jul 2016 11:40:10 -0500
From:	"Eric W. Biederman" <ebiederm@...ssion.com>
To:	Linux Containers <containers@...ts.linux-foundation.org>
Cc:	Andy Lutomirski <luto@...capital.net>, Jann Horn <jann@...jh.net>,
	Kees Cook <keescook@...omium.org>,
	Nikolay Borisov <kernel@...p.com>,
	"Serge E. Hallyn" <serge@...lyn.com>,
	Seth Forshee <seth.forshee@...onical.com>,
	linux-fsdevel@...r.kernel.org, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-api@...r.kernel.org,
	"Eric W. Biederman" <ebiederm@...ssion.com>
Subject: [PATCH v2 06/10] utsns: Add a limit on the number of uts namespaces

Signed-off-by: "Eric W. Biederman" <ebiederm@...ssion.com>
---
 include/linux/user_namespace.h |  1 +
 kernel/user_namespace.c        |  1 +
 kernel/utsname.c               | 31 ++++++++++++++++++++++++++-----
 3 files changed, 28 insertions(+), 5 deletions(-)

diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h
index 47733637741a..bed2506081fe 100644
--- a/include/linux/user_namespace.h
+++ b/include/linux/user_namespace.h
@@ -25,6 +25,7 @@ struct uid_gid_map {	/* 64 bytes -- 1 cache line */
 enum ucounts {
 	UCOUNT_USER_NAMESPACES,
 	UCOUNT_PID_NAMESPACES,
+	UCOUNT_UTS_NAMESPACES,
 	UCOUNT_COUNTS,
 };
 
diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
index 02a03ead7afc..6b205c24e888 100644
--- a/kernel/user_namespace.c
+++ b/kernel/user_namespace.c
@@ -78,6 +78,7 @@ static int count_max = COUNT_MAX;
 static struct ctl_table userns_table[] = {
 	UCOUNT_ENTRY("max_user_namespaces"),
 	UCOUNT_ENTRY("max_pid_namespaces"),
+	UCOUNT_ENTRY("max_uts_namespaces"),
 	{ }
 };
 #endif /* CONFIG_SYSCTL */
diff --git a/kernel/utsname.c b/kernel/utsname.c
index 831ea7108232..4f13c0419d64 100644
--- a/kernel/utsname.c
+++ b/kernel/utsname.c
@@ -17,6 +17,16 @@
 #include <linux/user_namespace.h>
 #include <linux/proc_ns.h>
 
+static bool inc_uts_namespaces(struct user_namespace *ns)
+{
+	return inc_ucount(ns, UCOUNT_UTS_NAMESPACES);
+}
+
+static void dec_uts_namespaces(struct user_namespace *ns)
+{
+	dec_ucount(ns, UCOUNT_UTS_NAMESPACES);
+}
+
 static struct uts_namespace *create_uts_ns(void)
 {
 	struct uts_namespace *uts_ns;
@@ -38,15 +48,18 @@ static struct uts_namespace *clone_uts_ns(struct user_namespace *user_ns,
 	struct uts_namespace *ns;
 	int err;
 
+	err = -ENFILE;
+	if (!inc_uts_namespaces(user_ns))
+		goto fail;
+
+	err = -ENOMEM;
 	ns = create_uts_ns();
 	if (!ns)
-		return ERR_PTR(-ENOMEM);
+		goto fail_dec;
 
 	err = ns_alloc_inum(&ns->ns);
-	if (err) {
-		kfree(ns);
-		return ERR_PTR(err);
-	}
+	if (err)
+		goto fail_free;
 
 	ns->ns.ops = &utsns_operations;
 
@@ -55,6 +68,13 @@ static struct uts_namespace *clone_uts_ns(struct user_namespace *user_ns,
 	ns->user_ns = get_user_ns(user_ns);
 	up_read(&uts_sem);
 	return ns;
+
+fail_free:
+	kfree(ns);
+fail_dec:
+	dec_uts_namespaces(user_ns);
+fail:
+	return ERR_PTR(err);
 }
 
 /*
@@ -85,6 +105,7 @@ void free_uts_ns(struct kref *kref)
 	struct uts_namespace *ns;
 
 	ns = container_of(kref, struct uts_namespace, kref);
+	dec_uts_namespaces(ns->user_ns);
 	put_user_ns(ns->user_ns);
 	ns_free_inum(&ns->ns);
 	kfree(ns);
-- 
2.8.3