From 84ec2d3b67dffadd2c0c839a1fab621e63ce0b68 Mon Sep 17 00:00:00 2001
From: Kyle Evans <kevans@FreeBSD.org>
Date: Fri, 4 Sep 2026 10:26:35 -0500
Subject: [PATCH] iuserboot: bump the interface to v6, add an
 accept_interpreter callback

If an explicit loader wasn't requested, then bhyveload(8) maintains a
/boot handle that it can use for swapping to a different flavor.  This
means that we expose all of the host /boot to the sandbox for the
duration of script execution.

Add a callback to ack that we're OK with the interpreter so that
bhyveload(8) can release the bootfd.  This is worth doing because it's
prior to guest script execution, so we're still running a reasonably
untainted process.

Reviewed by:	imp, jhb

(cherry picked from commit 619d09217720cb82f562b51e98576438dc11c830)
---
 stand/userboot/userboot.h      | 12 ++++++++++++
 stand/userboot/userboot/main.c |  2 ++
 usr.sbin/bhyveload/bhyveload.c | 23 ++++++++++++++++++-----
 3 files changed, 32 insertions(+), 5 deletions(-)

diff --git a/stand/userboot/userboot.h b/stand/userboot/userboot.h
index 34e8cb1d4bb2..1204f5e87f6f 100644
--- a/stand/userboot/userboot.h
+++ b/stand/userboot/userboot.h
@@ -46,6 +46,13 @@
  */
 #define	USERBOOT_VERSION_5      5
 
+/*
+ * Version 6 added a callback for indicating that the guest
+ * is OK with the existing interpreter, so the host can close associated
+ * resources.  The callback structure is still backward compatible.
+ */
+#define	USERBOOT_VERSION_6      6
+
 /*
  * Exit codes from the loader
  */
@@ -225,4 +232,9 @@ struct loader_callbacks {
 	 * Version 5 addition.
 	 */
 	void	(*swap_interpreter)(void *arg, const char *interp);
+
+	/*
+	 * Version 6 addition.
+	 */
+	void	(*accept_interpreter)(void *arg);
 };
diff --git a/stand/userboot/userboot/main.c b/stand/userboot/userboot/main.c
index b518e18020f8..985933bf51e9 100644
--- a/stand/userboot/userboot/main.c
+++ b/stand/userboot/userboot/main.c
@@ -217,6 +217,8 @@ loader_main(struct loader_callbacks *cb, void *arg, int version, int ndisks)
 	 */
 	if (version >= USERBOOT_VERSION_5)
 		check_interpreter();
+	if (version >= USERBOOT_VERSION_6)
+		CALLBACK(accept_interpreter);
 
 	if (setjmp(jb))
 		return;
diff --git a/usr.sbin/bhyveload/bhyveload.c b/usr.sbin/bhyveload/bhyveload.c
index 3f29d642461d..ebc6f9618691 100644
--- a/usr.sbin/bhyveload/bhyveload.c
+++ b/usr.sbin/bhyveload/bhyveload.c
@@ -102,6 +102,7 @@ enum {
 static struct termios term, oldterm;
 static int disk_fd[NDISKS];
 static int ndisks;
+static int bootfd = -1;
 static int consin_fd, consout_fd;
 static int hostbase_fd = -1;
 
@@ -652,6 +653,16 @@ cb_swap_interpreter(void *arg __unused, const char *interp_req)
 	longjmp(jb, JMP_SWAPLOADER);
 }
 
+static void
+cb_accept_interpreter(void *arg __unused)
+{
+	if (bootfd == -1)
+		return;
+
+	close(bootfd);
+	bootfd = -1;
+}
+
 static struct loader_callbacks cb = {
 	.getc = cb_getc,
 	.putc = cb_putc,
@@ -689,6 +700,9 @@ static struct loader_callbacks cb = {
 
 	/* Version 5 additions */
 	.swap_interpreter = cb_swap_interpreter,
+
+	/* Version 6 additions */
+	.accept_interpreter = cb_accept_interpreter,
 };
 
 static int
@@ -790,7 +804,7 @@ hostbase_open(const char *base)
 }
 
 static void
-loader_open(int bootfd)
+loader_open(void)
 {
 	int fd;
 
@@ -820,9 +834,8 @@ main(int argc, char** argv)
 {
 	void (*func)(struct loader_callbacks *, void *, int, int);
 	uint64_t mem_size;
-	int bootfd, opt, error, memflags, need_reinit;
+	int opt, error, memflags, need_reinit;
 
-	bootfd = -1;
 	progname = basename(argv[0]);
 
 	memflags = 0;
@@ -950,7 +963,7 @@ main(int argc, char** argv)
 	if (error)
 		err(1, "vm_setup_memory");
 
-	loader_open(bootfd);
+	loader_open();
 	func = dlsym(loader_hdl, "loader_main");
 	if (!func)
 		errx(1, "dlsym: %s", dlerror());
@@ -965,7 +978,7 @@ main(int argc, char** argv)
 	addenv("smbios.bios.vendor=BHYVE");
 	addenv("boot_serial=1");
 
-	func(&cb, NULL, USERBOOT_VERSION_5, ndisks);
+	func(&cb, NULL, USERBOOT_VERSION_6, ndisks);
 
 	free(loader);
 	return (0);