Re: [PATCH RFC 4/5] SUNRPC: Support TLS handshake in the server-side TCP socket code

[Chuck Lever III <chuck.lever@oracle.com>]

> On Mar 21, 2023, at 7:43 AM, Jeff Layton <jlayton@kernel.org> wrote:
> 
> On Mon, 2023-03-20 at 10:24 -0400, Chuck Lever wrote:
>> From: Chuck Lever <chuck.lever@oracle.com>
>> 
>> This patch adds opportunitistic RPC-with-TLS to the Linux in-kernel
>> NFS server. If the client requests RPC-with-TLS and the user space
>> handshake agent is running, the server will set up a TLS session.
>> 
>> There are no policy settings yet. For example, the server cannot
>> yet require the use of RPC-with-TLS to access its data.
>> 
>> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
>> ---
>> include/linux/sunrpc/svc_xprt.h |    5 ++
>> include/linux/sunrpc/svcsock.h  |    2 +
>> include/trace/events/sunrpc.h   |   16 ++++++-
>> net/sunrpc/svc_xprt.c           |    5 ++
>> net/sunrpc/svcauth_unix.c       |   11 ++++-
>> net/sunrpc/svcsock.c            |   91 +++++++++++++++++++++++++++++++++++++++
>> 6 files changed, 125 insertions(+), 5 deletions(-)
>> 
>> diff --git a/include/linux/sunrpc/svc_xprt.h b/include/linux/sunrpc/svc_xprt.h
>> index 775368802762..867479204840 100644
>> --- a/include/linux/sunrpc/svc_xprt.h
>> +++ b/include/linux/sunrpc/svc_xprt.h
>> @@ -27,7 +27,7 @@ struct svc_xprt_ops {
>> 	void		(*xpo_detach)(struct svc_xprt *);
>> 	void		(*xpo_free)(struct svc_xprt *);
>> 	void		(*xpo_kill_temp_xprt)(struct svc_xprt *);
>> -	void		(*xpo_start_tls)(struct svc_xprt *);
>> +	void		(*xpo_handshake)(struct svc_xprt *xprt);
>> };
>> 
>> struct svc_xprt_class {
>> @@ -70,6 +70,9 @@ struct svc_xprt {
>> #define XPT_LOCAL	12		/* connection from loopback interface */
>> #define XPT_KILL_TEMP   13		/* call xpo_kill_temp_xprt before closing */
>> #define XPT_CONG_CTRL	14		/* has congestion control */
>> +#define XPT_HANDSHAKE	15		/* xprt requests a handshake */
>> +#define XPT_TLS_SESSION	16		/* transport-layer security established */
>> +#define XPT_PEER_AUTH	17		/* peer has been authenticated */
>> 
>> 	struct svc_serv		*xpt_server;	/* service for transport */
>> 	atomic_t    	    	xpt_reserved;	/* space on outq that is rsvd */
>> diff --git a/include/linux/sunrpc/svcsock.h b/include/linux/sunrpc/svcsock.h
>> index bcc555c7ae9c..1175e1c38bac 100644
>> --- a/include/linux/sunrpc/svcsock.h
>> +++ b/include/linux/sunrpc/svcsock.h
>> @@ -38,6 +38,8 @@ struct svc_sock {
>> 	/* Number of queued send requests */
>> 	atomic_t		sk_sendqlen;
>> 
>> +	struct completion	sk_handshake_done;
>> +
>> 	struct page *		sk_pages[RPCSVC_MAXPAGES];	/* received data */
>> };
>> 
>> diff --git a/include/trace/events/sunrpc.h b/include/trace/events/sunrpc.h
>> index cf286a0a17d0..2667a8db4811 100644
>> --- a/include/trace/events/sunrpc.h
>> +++ b/include/trace/events/sunrpc.h
>> @@ -1948,7 +1948,10 @@ TRACE_EVENT(svc_stats_latency,
>> 		{ BIT(XPT_CACHE_AUTH),		"CACHE_AUTH" },		\
>> 		{ BIT(XPT_LOCAL),		"LOCAL" },		\
>> 		{ BIT(XPT_KILL_TEMP),		"KILL_TEMP" },		\
>> -		{ BIT(XPT_CONG_CTRL),		"CONG_CTRL" })
>> +		{ BIT(XPT_CONG_CTRL),		"CONG_CTRL" },		\
>> +		{ BIT(XPT_HANDSHAKE),		"HANDSHAKE" },		\
>> +		{ BIT(XPT_TLS_SESSION),		"TLS_SESSION" },	\
>> +		{ BIT(XPT_PEER_AUTH),		"PEER_AUTH" })
>> 
>> TRACE_EVENT(svc_xprt_create_err,
>> 	TP_PROTO(
>> @@ -2081,6 +2084,17 @@ DEFINE_SVC_XPRT_EVENT(close);
>> DEFINE_SVC_XPRT_EVENT(detach);
>> DEFINE_SVC_XPRT_EVENT(free);
>> 
>> +#define DEFINE_SVC_TLS_EVENT(name) \
>> +	DEFINE_EVENT(svc_xprt_event, svc_tls_##name, \
>> +		TP_PROTO(const struct svc_xprt *xprt), \
>> +		TP_ARGS(xprt))
>> +
>> +DEFINE_SVC_TLS_EVENT(start);
>> +DEFINE_SVC_TLS_EVENT(upcall);
>> +DEFINE_SVC_TLS_EVENT(unavailable);
>> +DEFINE_SVC_TLS_EVENT(not_started);
>> +DEFINE_SVC_TLS_EVENT(timed_out);
>> +
>> TRACE_EVENT(svc_xprt_accept,
>> 	TP_PROTO(
>> 		const struct svc_xprt *xprt,
>> diff --git a/net/sunrpc/svc_xprt.c b/net/sunrpc/svc_xprt.c
>> index ba629297da4e..b68c04dbf876 100644
>> --- a/net/sunrpc/svc_xprt.c
>> +++ b/net/sunrpc/svc_xprt.c
>> @@ -427,7 +427,7 @@ static bool svc_xprt_ready(struct svc_xprt *xprt)
>> 
>> 	if (xpt_flags & BIT(XPT_BUSY))
>> 		return false;
>> -	if (xpt_flags & (BIT(XPT_CONN) | BIT(XPT_CLOSE)))
>> +	if (xpt_flags & (BIT(XPT_CONN) | BIT(XPT_CLOSE) | BIT(XPT_HANDSHAKE)))
>> 		return true;
>> 	if (xpt_flags & (BIT(XPT_DATA) | BIT(XPT_DEFERRED))) {
>> 		if (xprt->xpt_ops->xpo_has_wspace(xprt) &&
>> @@ -829,6 +829,9 @@ static int svc_handle_xprt(struct svc_rqst *rqstp, struct svc_xprt *xprt)
>> 			module_put(xprt->xpt_class->xcl_owner);
>> 		}
>> 		svc_xprt_received(xprt);
>> +	} else if (test_bit(XPT_HANDSHAKE, &xprt->xpt_flags)) {
>> +		xprt->xpt_ops->xpo_handshake(xprt);
>> +		svc_xprt_received(xprt);
>> 	} else if (svc_xprt_reserve_slot(rqstp, xprt)) {
>> 		/* XPT_DATA|XPT_DEFERRED case: */
>> 		dprintk("svc: server %p, pool %u, transport %p, inuse=%d\n",
>> diff --git a/net/sunrpc/svcauth_unix.c b/net/sunrpc/svcauth_unix.c
>> index 983c5891cb56..374995201df4 100644
>> --- a/net/sunrpc/svcauth_unix.c
>> +++ b/net/sunrpc/svcauth_unix.c
>> @@ -17,8 +17,9 @@
>> #include <net/ipv6.h>
>> #include <linux/kernel.h>
>> #include <linux/user_namespace.h>
>> -#define RPCDBG_FACILITY	RPCDBG_AUTH
>> +#include <trace/events/sunrpc.h>
>> 
>> +#define RPCDBG_FACILITY	RPCDBG_AUTH
>> 
>> #include "netns.h"
>> 
>> @@ -823,6 +824,7 @@ svcauth_tls_accept(struct svc_rqst *rqstp)
>> {
>> 	struct xdr_stream *xdr = &rqstp->rq_arg_stream;
>> 	struct svc_cred	*cred = &rqstp->rq_cred;
>> +	struct svc_xprt *xprt = rqstp->rq_xprt;
>> 	u32 flavor, len;
>> 	void *body;
>> 	__be32 *p;
>> @@ -856,14 +858,19 @@ svcauth_tls_accept(struct svc_rqst *rqstp)
>> 	if (cred->cr_group_info == NULL)
>> 		return SVC_CLOSE;
>> 
>> -	if (rqstp->rq_xprt->xpt_ops->xpo_start_tls) {
>> +	if (xprt->xpt_ops->xpo_handshake) {
>> 		p = xdr_reserve_space(&rqstp->rq_res_stream, XDR_UNIT * 2 + 8);
>> 		if (!p)
>> 			return SVC_CLOSE;
>> +		trace_svc_tls_start(xprt);
>> 		*p++ = rpc_auth_null;
>> 		*p++ = cpu_to_be32(8);
>> 		memcpy(p, "STARTTLS", 8);
>> +
>> +		set_bit(XPT_HANDSHAKE, &xprt->xpt_flags);
>> +		svc_xprt_enqueue(xprt);
>> 	} else {
>> +		trace_svc_tls_unavailable(xprt);
>> 		if (xdr_stream_encode_opaque_auth(&rqstp->rq_res_stream,
>> 						  RPC_AUTH_NULL, NULL, 0) < 0)
>> 			return SVC_CLOSE;
>> diff --git a/net/sunrpc/svcsock.c b/net/sunrpc/svcsock.c
>> index b6df73cb706a..16ba8d6ab20e 100644
>> --- a/net/sunrpc/svcsock.c
>> +++ b/net/sunrpc/svcsock.c
>> @@ -44,9 +44,11 @@
>> #include <net/tcp.h>
>> #include <net/tcp_states.h>
>> #include <net/tls.h>
>> +#include <net/handshake.h>
>> #include <linux/uaccess.h>
>> #include <linux/highmem.h>
>> #include <asm/ioctls.h>
>> +#include <linux/key.h>
>> 
>> #include <linux/sunrpc/types.h>
>> #include <linux/sunrpc/clnt.h>
>> @@ -64,6 +66,7 @@
>> 
>> #define RPCDBG_FACILITY	RPCDBG_SVCXPRT
>> 
>> +#define SVC_HANDSHAKE_TO	(20U * HZ)
>> 
>> static struct svc_sock *svc_setup_socket(struct svc_serv *, struct socket *,
>> 					 int flags);
>> @@ -360,6 +363,8 @@ static void svc_data_ready(struct sock *sk)
>> 		rmb();
>> 		svsk->sk_odata(sk);
>> 		trace_svcsock_data_ready(&svsk->sk_xprt, 0);
>> +		if (test_bit(XPT_HANDSHAKE, &svsk->sk_xprt.xpt_flags))
>> +			return;
>> 		if (!test_and_set_bit(XPT_DATA, &svsk->sk_xprt.xpt_flags))
>> 			svc_xprt_enqueue(&svsk->sk_xprt);
>> 	}
>> @@ -397,6 +402,89 @@ static void svc_tcp_kill_temp_xprt(struct svc_xprt *xprt)
>> 	sock_no_linger(svsk->sk_sock->sk);
>> }
>> 
>> +/**
>> + * svc_tcp_handshake_done - Handshake completion handler
>> + * @data: address of xprt to wake
>> + * @status: status of handshake
>> + * @peerid: serial number of key containing the remote peer's identity
>> + *
>> + * If a security policy is specified as an export option, we don't
>> + * have a specific export here to check. So we set a "TLS session
>> + * is present" flag on the xprt and let an upper layer enforce local
>> + * security policy.
>> + */
>> +static void svc_tcp_handshake_done(void *data, int status, key_serial_t peerid)
>> +{
>> +	struct svc_xprt *xprt = data;
>> +	struct svc_sock *svsk = container_of(xprt, struct svc_sock, sk_xprt);
>> +
>> +	if (!status) {
>> +		if (peerid != TLS_NO_PEERID)
>> +			set_bit(XPT_PEER_AUTH, &xprt->xpt_flags);
>> +		set_bit(XPT_TLS_SESSION, &xprt->xpt_flags);
>> +	}
>> +	clear_bit(XPT_HANDSHAKE, &xprt->xpt_flags);
>> +	complete_all(&svsk->sk_handshake_done);
>> +}
>> +
>> +/**
>> + * svc_tcp_handshake - Perform a transport-layer security handshake
>> + * @xprt: connected transport endpoint
>> + *
>> + */
>> +static void svc_tcp_handshake(struct svc_xprt *xprt)
>> +{
>> +	struct svc_sock *svsk = container_of(xprt, struct svc_sock, sk_xprt);
>> +	struct tls_handshake_args args = {
>> +		.ta_sock	= svsk->sk_sock,
>> +		.ta_done	= svc_tcp_handshake_done,
>> +		.ta_data	= xprt,
>> +	};
>> +	int ret;
>> +
>> +	trace_svc_tls_upcall(xprt);
>> +
>> +	clear_bit(XPT_TLS_SESSION, &xprt->xpt_flags);
>> +	init_completion(&svsk->sk_handshake_done);
>> +	smp_wmb();
>> +
>> +	ret = tls_server_hello_x509(&args, GFP_KERNEL);
>> +	if (ret) {
>> +		trace_svc_tls_not_started(xprt);
>> +		goto out_failed;
>> +	}
>> +
>> +	ret = wait_for_completion_interruptible_timeout(&svsk->sk_handshake_done,
>> +							SVC_HANDSHAKE_TO);
> 
> Just curious: is this 20s timeout mandated by the spec?

The spec doesn't mandate a timeout. I simply wanted
to guarantee forward progress.


> It seems like a long time to block a kernel thread if so.

It's about the same as the client side timeout, fwiw.


> Do we need to be concerned
> with DoS attacks here? Could a client initiate handshakes and then stop
> communicating, forcing the server to tie up threads with these 20s
> waits?

I think a malicious client can do all kinds of similar things
already. Do you have a particular timeout value in mind, or
is there some other mechanism we can use to better bullet-
proof this aspect of the handshake? I'm open to suggestion.


>> +	if (ret <= 0) {
>> +		if (tls_handshake_cancel(svsk->sk_sock)) {
>> +			trace_svc_tls_timed_out(xprt);
>> +			goto out_close;
>> +		}
>> +	}
>> +
>> +	if (!test_bit(XPT_TLS_SESSION, &xprt->xpt_flags)) {
>> +		trace_svc_tls_unavailable(xprt);
>> +		goto out_close;
>> +	}
>> +
>> +	/*
>> +	 * Mark the transport ready in case the remote sent RPC
>> +	 * traffic before the kernel received the handshake
>> +	 * completion downcall.
>> +	 */
>> +	set_bit(XPT_DATA, &xprt->xpt_flags);
>> +	svc_xprt_enqueue(xprt);
>> +	return;
>> +
>> +out_close:
>> +	set_bit(XPT_CLOSE, &xprt->xpt_flags);
>> +out_failed:
>> +	clear_bit(XPT_HANDSHAKE, &xprt->xpt_flags);
>> +	set_bit(XPT_DATA, &xprt->xpt_flags);
>> +	svc_xprt_enqueue(xprt);
>> +}
>> +
>> /*
>>  * See net/ipv6/ip_sockglue.c : ip_cmsg_recv_pktinfo
>>  */
>> @@ -1260,6 +1348,7 @@ static const struct svc_xprt_ops svc_tcp_ops = {
>> 	.xpo_has_wspace = svc_tcp_has_wspace,
>> 	.xpo_accept = svc_tcp_accept,
>> 	.xpo_kill_temp_xprt = svc_tcp_kill_temp_xprt,
>> +	.xpo_handshake = svc_tcp_handshake,
>> };
>> 
>> static struct svc_xprt_class svc_tcp_class = {
>> @@ -1584,6 +1673,8 @@ static void svc_sock_free(struct svc_xprt *xprt)
>> {
>> 	struct svc_sock *svsk = container_of(xprt, struct svc_sock, sk_xprt);
>> 
>> +	tls_handshake_cancel(svsk->sk_sock);
>> +
>> 	if (svsk->sk_sock->file)
>> 		sockfd_put(svsk->sk_sock);
>> 	else
>> 
>> 
> 
> -- 
> Jeff Layton <jlayton@kernel.org>

--
Chuck Lever