sysfs: Restrict mounting sysfs

Don't allow mounting sysfs unless the caller has CAP_SYS_ADMIN rights
over the net namespace.  The principle here is if you create or have
capabilities over it you can mount it, otherwise you get to live with
what other people have mounted.

Instead of testing this with a straight forward ns_capable call,
perform this check the long and torturous way with kobject helpers,
this keeps direct knowledge of namespaces out of sysfs, and preserves
the existing sysfs abstractions.

Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>

1 files changed, 9 insertions, 3 deletions

diff --git a/fs/sysfs/mount.c b/fs/sysfs/mount.c
index 4a2da3a4b1b1..8c69ef49c7f3 100644
--- a/fs/sysfs/mount.c
+++ b/fs/sysfs/mount.c
@@ -112,9 +112,15 @@ static struct dentry *sysfs_mount(struct file_system_type *fs_type,
         struct super_block *sb;
         int error;
 
-        if (!(flags & MS_KERNMOUNT) && !capable(CAP_SYS_ADMIN) &&
-            !fs_fully_visible(fs_type))
-                return ERR_PTR(-EPERM);
+        if (!(flags & MS_KERNMOUNT)) {
+                if (!capable(CAP_SYS_ADMIN) && !fs_fully_visible(fs_type))
+                        return ERR_PTR(-EPERM);
+
+                for (type = KOBJ_NS_TYPE_NONE; type < KOBJ_NS_TYPES; type++) {
+                        if (!kobj_ns_current_may_mount(type))
+                                return ERR_PTR(-EPERM);
+                }
+        }
 
         info = kzalloc(sizeof(*info), GFP_KERNEL);
         if (!info)