• Chuck Lever's avatar
    net/handshake: Create a NETLINK service for handling handshake requests · 3b3009ea
    Chuck Lever authored
    When a kernel consumer needs a transport layer security session, it
    first needs a handshake to negotiate and establish a session. This
    negotiation can be done in user space via one of the several
    existing library implementations, or it can be done in the kernel.
    
    No in-kernel handshake implementations yet exist. In their absence,
    we add a netlink service that can:
    
    a. Notify a user space daemon that a handshake is needed.
    
    b. Once notified, the daemon calls the kernel back via this
       netlink service to get the handshake parameters, including an
       open socket on which to establish the session.
    
    c. Once the handshake is complete, the daemon reports the
       session status and other information via a second netlink
       operation. This operation marks that it is safe for the
       kernel to use the open socket and the security session
       established there.
    
    The notification service uses a multicast group. Each handshake
    mechanism (eg, tlshd) adopts its own group number so that the
    handshake services are completely independent of one another. The
    kernel can then tell via netlink_has_listeners() whether a handshake
    service is active and prepared to handle a handshake request.
    
    A new netlink operation, ACCEPT, acts like accept(2) in that it
    instantiates a file descriptor in the user space daemon's fd table.
    If this operation is successful, the reply carries the fd number,
    which can be treated as an open and ready file descriptor.
    
    While user space is performing the handshake, the kernel keeps its
    muddy paws off the open socket. A second new netlink operation,
    DONE, indicates that the user space daemon is finished with the
    socket and it is safe for the kernel to use again. The operation
    also indicates whether a session was established successfully.
    Signed-off-by: default avatarChuck Lever <chuck.lever@oracle.com>
    Signed-off-by: default avatarJakub Kicinski <kuba@kernel.org>
    3b3009ea
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