auditdistd: Use fixed-length protocol names

All communication between auditdistd senders and receivers and
internally between auditdistd and its worker children passes through the
same pair of send / receive functions.  The receive function uses
recv(2) with the MSG_WAITALL flag, which in theory means we should never
get a short read.  However, when handing off a socket to a worker child,
we also pass a variable-length string identifying the type of socket
we're passing, and reading this string relies on a short read.  This
used to work because the arrival of the descriptor would interrupt the
recv(2) call, but this bug was fixed when the AF_UNIX code was rewritten
a while ago and auditdistd has been broken ever since.

Fixing the length of the protocol name to four characters including the
terminating null solves the short-read bug by never requiring a short
read (nothing else in auditdistd requires one).

PR:		296107
MFC after:	1 week
Reviewed by:	js, kevans
Differential Revision:	https://reviews.freebsd.org/D59565

contrib/openbsm/bin/auditdistd/proto.c

@@ -269,7 +269,6 @@ proto_recv(const struct proto_conn *conn, void *data, size_t size)
 int
 proto_connection_send(const struct proto_conn *conn, struct proto_conn *mconn)
 {
-	const char *protoname;
 	int error, fd;
 
 	PJDLOG_ASSERT(conn != NULL);
@@ -281,11 +280,9 @@ proto_connection_send(const struct proto_conn *conn, struct proto_conn *mconn)
 	PJDLOG_ASSERT(mconn->pc_proto != NULL);
 	fd = proto_descriptor(mconn);
 	PJDLOG_ASSERT(fd >= 0);
-	protoname = mconn->pc_proto->prt_name;
-	PJDLOG_ASSERT(protoname != NULL);
 
 	error = conn->pc_proto->prt_send(conn->pc_ctx,
-	    (const unsigned char *)protoname, strlen(protoname) + 1, fd);
+	    mconn->pc_proto->prt_name, sizeof(mconn->pc_proto->prt_name), fd);
 	proto_close(mconn);
 	if (error != 0) {
 		errno = error;
@@ -303,7 +300,7 @@ proto_wrap(const char *protoname, bool client, int fd,
 	int error;
 
 	TAILQ_FOREACH(proto, &protos, prt_next) {
-		if (strcmp(proto->prt_name, protoname) == 0)
+		if (memcmp(proto->prt_name, protoname, sizeof(proto->prt_name)) == 0)
 			break;
 	}
 	if (proto == NULL) {
@@ -332,7 +329,7 @@ int
 proto_connection_recv(const struct proto_conn *conn, bool client,
     struct proto_conn **newconnp)
 {
-	char protoname[128];
+	char protoname[sizeof(conn->pc_proto->prt_name)];
 	int error, fd;
 
 	PJDLOG_ASSERT(conn != NULL);
@@ -341,10 +338,8 @@ proto_connection_recv(const struct proto_conn *conn, bool client,
 	PJDLOG_ASSERT(conn->pc_proto->prt_recv != NULL);
 	PJDLOG_ASSERT(newconnp != NULL);
 
-	bzero(protoname, sizeof(protoname));
-
 	error = conn->pc_proto->prt_recv(conn->pc_ctx,
-	    (unsigned char *)protoname, sizeof(protoname) - 1, &fd);
+	    protoname, sizeof(protoname), &fd);
 	if (error != 0) {
 		errno = error;
 		return (-1);

contrib/openbsm/bin/auditdistd/proto_impl.h

@@ -54,7 +54,7 @@ typedef void prt_close_t(void *);
 typedef int prt_exec_t(int, char *[]);
 
 struct proto {
-	const char		*prt_name;
+	char			 prt_name[4];
 	prt_connect_t		*prt_connect;
 	prt_connect_wait_t	*prt_connect_wait;
 	prt_server_t		*prt_server;

contrib/openbsm/bin/auditdistd/proto_socketpair.c

@@ -247,7 +247,7 @@ sp_close(void *ctx)
 }
 
 static struct proto sp_proto = {
-	.prt_name = "socketpair",
+	.prt_name = "skp",
 	.prt_connect = sp_connect,
 	.prt_wrap = sp_wrap,
 	.prt_send = sp_send,

contrib/openbsm/bin/auditdistd/proto_tls.c

@@ -854,7 +854,7 @@ tls_wrap(int fd, bool client, void **ctxp)
 	if (tlsctx == NULL)
 		return (errno);
 
-	if (proto_wrap("socketpair", client, fd, &sock) == -1) {
+	if (proto_wrap("skp", client, fd, &sock) == -1) {
 		error = errno;
 		free(tlsctx);
 		return (error);