security: prevent permission checking of file removal via sysfs_remove_group()

Prevent permission checking from being performed when the kernel wants to
unconditionally remove a sysfs group, by introducing an kernel-only variant
of lookup_one_len(), lookup_one_len_kern().

Additionally, as sysfs_remove_group() does not check the return value of
the lookup before using it, a BUG_ON has been added to pinpoint the cause
of any problems potentially caused by this (and as a form of annotation).

Signed-off-by: James Morris <jmorris@namei.org>
Cc: Nagendra Singh Tomar <nagendra_tomar@adaptec.com>
Cc: Tejun Heo <htejun@gmail.com>
Cc: Stephen Smalley <sds@tycho.nsa.gov>
Cc: Eric Paris <eparis@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 4 insertions, 2 deletions

diff --git a/fs/sysfs/group.c b/fs/sysfs/group.c
index b20951c93761..52eed2a7a5ef 100644
--- a/fs/sysfs/group.c
+++ b/fs/sysfs/group.c
@@ -70,9 +70,11 @@ void sysfs_remove_group(struct kobject * kobj,
 {
         struct dentry * dir;
 
-        if (grp->name)
-                dir = lookup_one_len(grp->name, kobj->dentry,
+        if (grp->name) {
+                dir = lookup_one_len_kern(grp->name, kobj->dentry,
                                 strlen(grp->name));
+                BUG_ON(IS_ERR(dir));
+        }
         else
                 dir = dget(kobj->dentry);