cgroup: initialize xattr before calling d_instantiate()
cgroup: initialize xattr before calling d_instantiate()

cgroup_create_file() calls d_instantiate(), which may decide to look
at the xattrs on the file. Smack always does this and SELinux can be
configured to do so.

But cgroup_add_file() didn't initialize xattrs before calling
cgroup_create_file(), which finally leads to dereferencing NULL
dentry->d_fsdata.

This bug has been there since cgroup xattr was introduced.

Cc: <4fbacc2fa0ffdbb11bf1ad6925b886ebd08dd15f@vger.kernel.org> # 3.8.x
Reported-by: Ivan Bulatovic <58c756e679613d5d98da315024cb8e9bcbb9c091@archlinux.us>
Reported-by: Casey Schaufler <77bc9a9984e6786c5799d7a71768cf023120ef76@schaufler-ca.com>
Signed-off-by: Li Zefan <a8167b9d27aca9c6624754deb52c4c6420eded04@huawei.com>
Signed-off-by: Tejun Heo <546b05909706652891a87f7bfe385ae147f61f91@kernel.org>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas