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Subject: [PATCH RFC 07/12] SUNRPC: Capture CMSG metadata on client-side
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From:   Chuck Lever <cel@kernel.org>
To:     anna.schumaker@netapp.com, trondmy@hammerspace.com
Cc:     Chuck Lever <chuck.lever@oracle.com>, linux-nfs@vger.kernel.org,
        kernel-tls-handshake@lists.linux.dev
Date:   Tue, 16 May 2023 15:41:25 -0400
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From: Chuck Lever <chuck.lever@oracle.com>

kTLS sockets use CMSG to report decryption errors and the need
for session re-keying.

For RPC-with-TLS, an "application data" message contains a ULP
payload, and that is passed along to the RPC client. An "alert"
message triggers connection reset. Everything else is discarded.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
---
 net/sunrpc/xprtsock.c |   49 +++++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 47 insertions(+), 2 deletions(-)

diff --git a/net/sunrpc/xprtsock.c b/net/sunrpc/xprtsock.c
index 37f608c2c0a0..6f2fc863b47e 100644
--- a/net/sunrpc/xprtsock.c
+++ b/net/sunrpc/xprtsock.c
@@ -47,6 +47,8 @@
 #include <net/checksum.h>
 #include <net/udp.h>
 #include <net/tcp.h>
+#include <net/tls.h>
+
 #include <linux/bvec.h>
 #include <linux/highmem.h>
 #include <linux/uio.h>
@@ -342,13 +344,56 @@ xs_alloc_sparse_pages(struct xdr_buf *buf, size_t want, gfp_t gfp)
 	return want;
 }
 
+static int
+xs_sock_process_cmsg(struct socket *sock, struct msghdr *msg,
+		     struct cmsghdr *cmsg, int ret)
+{
+	if (cmsg->cmsg_level == SOL_TLS &&
+	    cmsg->cmsg_type == TLS_GET_RECORD_TYPE) {
+		u8 content_type = *((u8 *)CMSG_DATA(cmsg));
+
+		switch (content_type) {
+		case TLS_RECORD_TYPE_DATA:
+			/* TLS sets EOR at the end of each application data
+			 * record, even though there might be more frames
+			 * waiting to be decrypted.
+			 */
+			msg->msg_flags &= ~MSG_EOR;
+			break;
+		case TLS_RECORD_TYPE_ALERT:
+			ret = -ENOTCONN;
+			break;
+		default:
+			ret = -EAGAIN;
+		}
+	}
+	return ret;
+}
+
+static int
+xs_sock_recv_cmsg(struct socket *sock, struct msghdr *msg, int flags)
+{
+	union {
+		struct cmsghdr	cmsg;
+		u8		buf[CMSG_SPACE(sizeof(u8))];
+	} u;
+	int ret;
+
+	msg->msg_control = &u;
+	msg->msg_controllen = sizeof(u);
+	ret = sock_recvmsg(sock, msg, flags);
+	if (msg->msg_controllen != sizeof(u))
+		ret = xs_sock_process_cmsg(sock, msg, &u.cmsg, ret);
+	return ret;
+}
+
 static ssize_t
 xs_sock_recvmsg(struct socket *sock, struct msghdr *msg, int flags, size_t seek)
 {
 	ssize_t ret;
 	if (seek != 0)
 		iov_iter_advance(&msg->msg_iter, seek);
-	ret = sock_recvmsg(sock, msg, flags);
+	ret = xs_sock_recv_cmsg(sock, msg, flags);
 	return ret > 0 ? ret + seek : ret;
 }
 
@@ -374,7 +419,7 @@ xs_read_discard(struct socket *sock, struct msghdr *msg, int flags,
 		size_t count)
 {
 	iov_iter_discard(&msg->msg_iter, ITER_DEST, count);
-	return sock_recvmsg(sock, msg, flags);
+	return xs_sock_recv_cmsg(sock, msg, flags);
 }
 
 #if ARCH_IMPLEMENTS_FLUSH_DCACHE_PAGE