[PATCH v5] nvme/069: add a test for multipath cdev lifetime

From: John Garry <[email protected]>

In [0], a fix was proposed for the NS and NS head (multipath) cdev
lifetime.

The issue was that fds for the nvme-generic cdev may exist after we tear
down the nvme-subsystem. Issuing an ioctl on that cdev may expose a
use-after-free.

This test recreates the method described in [0] to expose this issue
for NS head cdev.

First a fd is created by opening the nvme-generic cdev. Next we tear down
the nvme-subsystem. Finally we try to issue an ioctl on the cdev - without
the kernel fix in [0], this should trigger a KASAN warn.

[0] https://lore.kernel.org/linux-nvme/[email protected]/T/#me118851584fbcbb960795d0f04e2262e5a295613

Reviewed-by: Daniel Wagner <[email protected]>
Signed-off-by: John Garry <[email protected]>
---
Difference to v4:
- add specific error checking in nvme-delay-ioctl.c (Nilay)

Differences to v3:
- Add RB tag from Daniel (thanks!)
- Address comments from Shin'ichiro
 - script syntax
 - add copyright
 - wait command tweak

Difference to v2:
- remove sleep and use signal to sync

diff --git a/common/nvme b/common/nvme
index 15e9c3f..42301dc 100644
--- a/common/nvme
+++ b/common/nvme
@@ -300,6 +300,27 @@ _nvme_wait_subsys_removed() {
 	done
 }
 
+_nvme_find_subsys_nvme_generic() {
+	local subsyspath _subsysnqn subsyspathbase nvmegenericbase devicelink
+	local subsysnqn="$def_subsysnqn"
+
+	for subsyspath in /sys/class/nvme-subsystem/*; do
+		_subsysnqn=$(cat "${subsyspath}/subsysnqn" 2> /dev/null)
+		if [ "$subsysnqn" == "$_subsysnqn" ]; then
+			subsyspathbase="$(basename "$subsyspath")"
+			for nvmegeneric in /sys/class/nvme-generic/*; do
+				nvmegenericbase="$(basename "$nvmegeneric")"
+				devicelink="$(readlink "$nvmegeneric/device")"
+				if [[ "$devicelink" =~ $subsyspathbase ]]; then
+					echo "$nvmegenericbase"
+					break
+				fi
+			done
+			break
+		fi
+	done
+}
+
 _nvme_connect_subsys() {
 	local subsysnqn="$def_subsysnqn"
 	local hostnqn="$def_hostnqn"
diff --git a/src/.gitignore b/src/.gitignore
index 988d785..af9ebf6 100644
--- a/src/.gitignore
+++ b/src/.gitignore
@@ -14,3 +14,4 @@
 /nvme-passthrough-meta
 /ioctl-lbmd-query
 /nvme-passthru-admin-uring
+/nvme-delay-ioctl
diff --git a/src/Makefile b/src/Makefile
index d75daf1..4779ffd 100644
--- a/src/Makefile
+++ b/src/Makefile
@@ -18,6 +18,7 @@ C_TARGETS := \
 	loop_change_fd \
 	loop_get_status_null \
 	mount_clear_sock \
+	nvme-delay-ioctl \
 	nvme-passthrough-meta \
 	ioctl-lbmd-query \
 	nbdsetsize \
diff --git a/src/nvme-delay-ioctl.c b/src/nvme-delay-ioctl.c
new file mode 100644
index 0000000..28c4956
--- /dev/null
+++ b/src/nvme-delay-ioctl.c
@@ -0,0 +1,80 @@
+// SPDX-License-Identifier: GPL-3.0+
+// Copyright (C) 2026 John Garry
+
+/*
+ * Simple test to issue an ioctl some time after opening a cdev.
+ * This is to test lifetime of cdev, and whether we can handle
+ * removing the cdev while we have active fds.
+ */
+#define _GNU_SOURCE
+#include <dirent.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <signal.h>
+
+#include <inttypes.h>
+#include <sys/ioctl.h>
+#include <linux/types.h>
+
+#ifndef _LINUX_NVME_IOCTL_H
+#define _LINUX_NVME_IOCTL_H
+#define NVME_IOCTL_ID		_IO('N', 0x40)
+#endif /* _UAPI_LINUX_NVME_IOCTL_H */
+
+int main(int argc, char **argv)
+{
+	int fd, fd1;
+	int count;
+
+	if (argc < 2) {
+		fprintf(stderr, "usage: %s /dev/ngXnX", argv[0]);
+		return EINVAL;
+	}
+
+	fd = open(argv[1], O_RDONLY);
+	if (fd < 0)
+		return fd;
+
+	/*
+	 * Steps:
+	 * a. Signal to parent that we have opened the file so that it may
+	 *    start the teardown.
+	 * b. Try to open device until disallowed/gone.
+	 * c. Sleep to allow nvme-subsystem be torn down.
+	 * d. Issue the ioctl on original fd.
+	 */
+	kill(getppid(), SIGUSR2);
+	count = 0;
+	for (;;) {
+		fd1 = open(argv[1], O_RDONLY);
+		if (fd1 < 0) {
+			if (errno == EINTR)
+				continue;
+
+			if (errno == ENOENT || errno == ENODEV)
+				break;
+
+			perror("open");
+			close(fd);
+			return EINVAL;
+		}
+		close(fd1);
+		count++;
+		if (count > 10) {
+			fprintf(stderr, "%s still present", argv[0]);
+			close(fd);
+			return EINVAL;
+		}
+		usleep(500000);
+	}
+
+	ioctl(fd, NVME_IOCTL_ID);
+	close(fd);
+
+	return 0;
+}
diff --git a/tests/nvme/069 b/tests/nvme/069
new file mode 100755
index 0000000..61f796d
--- /dev/null
+++ b/tests/nvme/069
@@ -0,0 +1,61 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-3.0+
+# Copyright (C) 2026 John Garry
+#
+# Test NVMe multipath nvme-generic cdev lifetime behaves as expected.
+
+. tests/nvme/rc
+
+DESCRIPTION="NVMe multipath cdev lifetime test"
+CHECK_DMESG=1
+QUICK=1
+
+requires() {
+	_nvme_requires
+	_have_loop
+	_have_module_param_value nvme_core multipath Y
+	_require_nvme_trtype_is_fabrics
+	_have_kernel_options KASAN
+}
+
+set_conditions() {
+	_set_nvme_trtype "$@"
+}
+
+test() {
+	echo "Running ${TEST_NAME}"
+
+	local nvmedev
+	local loops=0
+	local quit=0
+	local nvmegeneric
+
+	_setup_nvmet
+	_nvmet_target_setup
+	_nvme_connect_subsys
+
+	nvmedev=$(_find_nvme_dev "${def_subsysnqn}")
+	nvmegeneric=$(_nvme_find_subsys_nvme_generic)
+
+	trap 'quit=1' USR2
+	# nvme-delay-ioctl will open the nvme-generic cdev, wait for teardown,
+	# and then issue an ioctl.
+	# We tear down the nvme-subsystem in the foreground so we can catch
+	# if the ioctl triggers a use-after-free KASAN warn.
+	src/nvme-delay-ioctl "/dev/$nvmegeneric" &
+
+	while [ "$quit" -ne 1 ]; do
+		sleep 0.1
+		((loops++))
+		if [[ "$loops" == "100" ]]; then
+			echo "no signal"
+			break
+		fi
+	done
+
+	_nvme_disconnect_ctrl "${nvmedev}"
+	_nvmet_target_cleanup
+	wait "$(jobs -p)"
+
+	echo "Test complete"
+}
diff --git a/tests/nvme/069.out b/tests/nvme/069.out
new file mode 100644
index 0000000..cd2e1fd
--- /dev/null
+++ b/tests/nvme/069.out
@@ -0,0 +1,2 @@
+Running nvme/069
+Test complete
-- 
2.43.7