7 files changed, 33 insertions, 23 deletions

diff --git a/fs/namespace.c b/fs/namespace.c
index 64627f883bf2..877e4277f496 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -2867,25 +2867,38 @@ bool current_chrooted(void)
         return chrooted;
 }
 
-void update_mnt_policy(struct user_namespace *userns)
+bool fs_fully_visible(struct file_system_type *type)
 {
         struct mnt_namespace *ns = current->nsproxy->mnt_ns;
         struct mount *mnt;
+        bool visible = false;
 
-        down_read(&namespace_sem);
+        if (unlikely(!ns))
+                return false;
+
+        namespace_lock();
         list_for_each_entry(mnt, &ns->list, mnt_list) {
-                switch (mnt->mnt.mnt_sb->s_magic) {
-                case SYSFS_MAGIC:
-                        userns->may_mount_sysfs = true;
-                        break;
-                case PROC_SUPER_MAGIC:
-                        userns->may_mount_proc = true;
-                        break;
+                struct mount *child;
+                if (mnt->mnt.mnt_sb->s_type != type)
+                        continue;
+
+                /* This mount is not fully visible if there are any child mounts
+                 * that cover anything except for empty directories.
+                 */
+                list_for_each_entry(child, &mnt->mnt_mounts, mnt_child) {
+                        struct inode *inode = child->mnt_mountpoint->d_inode;
+                        if (!S_ISDIR(inode->i_mode))
+                                goto next;
+                        if (inode->i_nlink != 2)
+                                goto next;
                 }
-                if (userns->may_mount_sysfs && userns->may_mount_proc)
-                        break;
+                visible = true;
+                goto found;
+        next:   ;
         }
-        up_read(&namespace_sem);
+found:
+        namespace_unlock();
+        return visible;
 }
 
 static void *mntns_get(struct task_struct *task)
diff --git a/fs/proc/root.c b/fs/proc/root.c
index 38bd5d423fcd..45e5fb7da09b 100644
--- a/fs/proc/root.c
+++ b/fs/proc/root.c
@@ -110,8 +110,11 @@ static struct dentry *proc_mount(struct file_system_type *fs_type,
                 ns = task_active_pid_ns(current);
                 options = data;
 
-                if (!current_user_ns()->may_mount_proc ||
-                    !ns_capable(ns->user_ns, CAP_SYS_ADMIN))
+                if (!capable(CAP_SYS_ADMIN) && !fs_fully_visible(fs_type))
+                        return ERR_PTR(-EPERM);
+
+                /* Does the mounter have privilege over the pid namespace? */
+                if (!ns_capable(ns->user_ns, CAP_SYS_ADMIN))
                         return ERR_PTR(-EPERM);
         }
 
diff --git a/fs/sysfs/mount.c b/fs/sysfs/mount.c
index afd83273e6ce..4a2da3a4b1b1 100644
--- a/fs/sysfs/mount.c
+++ b/fs/sysfs/mount.c
@@ -112,7 +112,8 @@ static struct dentry *sysfs_mount(struct file_system_type *fs_type,
         struct super_block *sb;
         int error;
 
-        if (!(flags & MS_KERNMOUNT) && !current_user_ns()->may_mount_sysfs)
+        if (!(flags & MS_KERNMOUNT) && !capable(CAP_SYS_ADMIN) &&
+            !fs_fully_visible(fs_type))
                 return ERR_PTR(-EPERM);
 
         info = kzalloc(sizeof(*info), GFP_KERNEL);
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 981874773e85..3050c620f062 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1897,6 +1897,7 @@ extern int vfs_ustat(dev_t, struct kstatfs *);
 extern int freeze_super(struct super_block *super);
 extern int thaw_super(struct super_block *super);
 extern bool our_mnt(struct vfsmount *mnt);
+extern bool fs_fully_visible(struct file_system_type *);
 
 extern int current_umask(void);
 
diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h
index b6b215f13b45..4ce009324933 100644
--- a/include/linux/user_namespace.h
+++ b/include/linux/user_namespace.h
@@ -26,8 +26,6 @@ struct user_namespace {
         kuid_t                  owner;
         kgid_t                  group;
         unsigned int            proc_inum;
-        bool                    may_mount_sysfs;
-        bool                    may_mount_proc;
 };
 
 extern struct user_namespace init_user_ns;
@@ -84,6 +82,4 @@ static inline void put_user_ns(struct user_namespace *ns)
 
 #endif
 
-void update_mnt_policy(struct user_namespace *userns);
-
 #endif /* _LINUX_USER_H */
diff --git a/kernel/user.c b/kernel/user.c
index 69b4c3d48cde..5bbb91988e69 100644
--- a/kernel/user.c
+++ b/kernel/user.c
@@ -51,8 +51,6 @@ struct user_namespace init_user_ns = {
         .owner = GLOBAL_ROOT_UID,
         .group = GLOBAL_ROOT_GID,
         .proc_inum = PROC_USER_INIT_INO,
-        .may_mount_sysfs = true,
-        .may_mount_proc = true,
 };
 EXPORT_SYMBOL_GPL(init_user_ns);
 
diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
index d8c30db06c5b..d58ad1e7a794 100644
--- a/kernel/user_namespace.c
+++ b/kernel/user_namespace.c
@@ -97,8 +97,6 @@ int create_user_ns(struct cred *new)
 
         set_cred_user_ns(new, ns);
 
-        update_mnt_policy(ns);
-
         return 0;
 }