Hello,
On 14/06/17 - 11:37:14, Dave Watson wrote:
> Add the infrustructure for attaching Upper Layer Protocols (ULPs) over TCP
> sockets. Based on a similar infrastructure in tcp_cong. The idea is that any
> ULP can add its own logic by changing the TCP proto_ops structure to its own
> methods.
>
> Example usage:
>
> setsockopt(sock, SOL_TCP, TCP_ULP, "tls", sizeof("tls"));
>
> modules will call:
> tcp_register_ulp(&tcp_tls_ulp_ops);
>
> to register/unregister their ulp, with an init function and name.
>
> A list of registered ulps will be returned by tcp_get_available_ulp, which is
> hooked up to /proc. Example:
>
> $ cat /proc/sys/net/ipv4/tcp_available_ulp
> tls
>
> There is currently no functionality to remove or chain ULPs, but
> it should be possible to add these in the future if needed.
>
> Signed-off-by: Boris Pismenny <borisp@xxxxxxxxxxxx>
> Signed-off-by: Dave Watson <davejwatson@xxxxxx>
> ---
> include/net/inet_connection_sock.h | 4 ++
> include/net/tcp.h | 25 +++++++
> include/uapi/linux/tcp.h | 1 +
> net/ipv4/Makefile | 2 +-
> net/ipv4/sysctl_net_ipv4.c | 25 +++++++
> net/ipv4/tcp.c | 28 ++++++++
> net/ipv4/tcp_ipv4.c | 2 +
> net/ipv4/tcp_ulp.c | 134 +++++++++++++++++++++++++++++++++++++
> 8 files changed, 220 insertions(+), 1 deletion(-)
> create mode 100644 net/ipv4/tcp_ulp.c
I know I'm pretty late to the game (and maybe this has already been
discussed but I couldn't find anything in the archives), but I am wondering
what the take is on potential races of the setsockopt() vs other system-calls.
For example one might race the setsockopt() with a sendmsg() and the sendmsg
might end up blocking on the lock_sock in tcp_sendmsg, waiting for
tcp_set_ulp() to finish changing sk_prot. When the setsockopt() finishes, we
are then inside tcp_sendmsg() coming directly from sendmsg(), while we
should have been in the ULP's sendmsg.
It seems like TLS-ULP is resilient to this (or at least, won't cause a panic),
but there might be more exotic users of ULP in the future, that change other
callbacks and then things might go wrong.
Thoughts?
Thanks,
Christoph
