5 files changed, 31 insertions, 17 deletions

diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h
index 32354b4b4b2b..4005877bb8b6 100644
--- a/include/linux/user_namespace.h
+++ b/include/linux/user_namespace.h
@@ -112,8 +112,9 @@ extern ssize_t proc_projid_map_write(struct file *, const char __user *, size_t,
 extern ssize_t proc_setgroups_write(struct file *, const char __user *, size_t, loff_t *);
 extern int proc_setgroups_show(struct seq_file *m, void *v);
 extern bool userns_may_setgroups(const struct user_namespace *ns);
+extern bool in_userns(const struct user_namespace *ancestor,
+		       const struct user_namespace *child);
 extern bool current_in_userns(const struct user_namespace *target_ns);
-
 struct ns_common *ns_get_owner(struct ns_common *ns);
 #else
 
@@ -144,6 +145,12 @@ static inline bool userns_may_setgroups(const struct user_namespace *ns)
 	return true;
 }
 
+static inline bool in_userns(const struct user_namespace *ancestor,
+			     const struct user_namespace *child)
+{
+	return true;
+}
+
 static inline bool current_in_userns(const struct user_namespace *target_ns)
 {
 	return true;
diff --git a/kernel/pid_namespace.c b/kernel/pid_namespace.c
index 74a5a7255b4d..4918314893bc 100644
--- a/kernel/pid_namespace.c
+++ b/kernel/pid_namespace.c
@@ -101,6 +101,10 @@ static struct pid_namespace *create_pid_namespace(struct user_namespace *user_ns
 	int i;
 	int err;
 
+	err = -EINVAL;
+	if (!in_userns(parent_pid_ns->user_ns, user_ns))
+		goto out;
+
 	err = -ENOSPC;
 	if (level > MAX_PID_NS_LEVEL)
 		goto out;
diff --git a/kernel/sys.c b/kernel/sys.c
index 2855ee73acd0..9aebc2935013 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -1896,15 +1896,11 @@ static int validate_prctl_map(struct prctl_mm_map *prctl_map)
 
 	/*
 	 * Finally, make sure the caller has the rights to
-	 * change /proc/pid/exe link: only local root should
+	 * change /proc/pid/exe link: only local sys admin should
 	 * be allowed to.
 	 */
 	if (prctl_map->exe_fd != (u32)-1) {
-		struct user_namespace *ns = current_user_ns();
-		const struct cred *cred = current_cred();
-
-		if (!uid_eq(cred->uid, make_kuid(ns, 0)) ||
-		    !gid_eq(cred->gid, make_kgid(ns, 0)))
+		if (!ns_capable(current_user_ns(), CAP_SYS_ADMIN))
 			goto out;
 	}
 
diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
index 2f735cbe05e8..c490f1e4313b 100644
--- a/kernel/user_namespace.c
+++ b/kernel/user_namespace.c
@@ -986,17 +986,21 @@ bool userns_may_setgroups(const struct user_namespace *ns)
 }
 
 /*
- * Returns true if @ns is the same namespace as or a descendant of
- * @target_ns.
+ * Returns true if @child is the same namespace or a descendant of
+ * @ancestor.
  */
+bool in_userns(const struct user_namespace *ancestor,
+	       const struct user_namespace *child)
+{
+	const struct user_namespace *ns;
+	for (ns = child; ns->level > ancestor->level; ns = ns->parent)
+		;
+	return (ns == ancestor);
+}
+
 bool current_in_userns(const struct user_namespace *target_ns)
 {
-	struct user_namespace *ns;
-	for (ns = current_user_ns(); ns; ns = ns->parent) {
-		if (ns == target_ns)
-			return true;
-	}
-	return false;
+	return in_userns(target_ns, current_user_ns());
 }
 
 static inline struct user_namespace *to_user_ns(struct ns_common *ns)
diff --git a/security/commoncap.c b/security/commoncap.c
index 7abebd782d5e..d59320282294 100644
--- a/security/commoncap.c
+++ b/security/commoncap.c
@@ -82,8 +82,11 @@ int cap_capable(const struct cred *cred, struct user_namespace *targ_ns,
 		if (ns == cred->user_ns)
 			return cap_raised(cred->cap_effective, cap) ? 0 : -EPERM;
 
-		/* Have we tried all of the parent namespaces? */
-		if (ns == &init_user_ns)
+		/*
+		 * If we're already at a lower level than we're looking for,
+		 * we're done searching.
+		 */
+		if (ns->level <= cred->user_ns->level)
 			return -EPERM;
 
 		/*