commoncap: Handle memory allocation failure.

commoncap: Handle memory allocation failure.

BugLink: http://bugs.launchpad.net/bugs/1775483
commit 1f5781725dcbb026438e77091c91a94f678c3522 upstream.

syzbot is reporting NULL pointer dereference at xattr_getsecurity() [1],
for cap_inode_getsecurity() is returning sizeof(struct vfs_cap_data) when
memory allocation failed. Return -ENOMEM if memory allocation failed.

[1] https://syzkaller.appspot.com/bug?id=a55ba438506fe68649a5f50d2d82d56b365e0107

Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Fixes: 8db6c34f1dbc8e06 ("Introduce v3 namespaced file capabilities")
Reported-by: syzbot <syzbot+9369930ca44f29e60e2d@syzkaller.appspotmail.com>
Cc: stable <stable@vger.kernel.org> # 4.14+
Acked-by: Serge E. Hallyn <serge@hallyn.com>
Acked-by: James Morris <james.morris@microsoft.com>
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>