selinux: fix a missing-check bug in selinux_add_mnt_opt( )

selinux: fix a missing-check bug in selinux_add_mnt_opt( )

commit e2e0e09758a6f7597de0f9b819647addfb71b6bd upstream.

In selinux_add_mnt_opt(), 'val' is allocated by kmemdup_nul(). It returns
NULL when fails. So 'val' should be checked. And 'mnt_opts' should be
freed when error.

Signed-off-by: Gen Zhang <blackgod016574@gmail.com>
Fixes: 757cbe597fe8 ("LSM: new method: ->sb_add_mnt_opt()")
Cc: <stable@vger.kernel.org>
[PM: fixed some indenting problems]
Signed-off-by: Paul Moore <paul@paul-moore.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>