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

[Eric W. Biederman]

Signed-off-by: "Eric W. Biederman" <ebied...@xmission.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