dmaengine: fix use-after-free in dma_chan_put() and dma_release_channel()grafted

When dma_device_put() drops the last reference on chan->device->ref,
dma_device_release() runs and may free the dma_device along with its
channels.

dma_chan_put() then still reads chan->device->owner via
dma_chan_to_owner() for the trailing module_put(). KASAN catches it:

	slab-use-after-free in dma_chan_put+0x3e6/0x4c0
	Read of size 8 by task insmod/6319
	Freed by task 6319:
	  kfree+0x225/0x470
	  dma_chan_put+0x395/0x4c0
	  dmaengine_put+0xf8/0x160

Cache the module owner in dma_chan_put() before the put so the trailing
module_put() does not need chan->device.

Fixes: 8ad342a86359 ("dmaengine: Add reference counting to dma_device struct")
Suggested-by: Sashiko <sashiko-bot@kernel.org>
Link: https://sashiko.dev/#/patchset/20260518-dmaengine-kref-fix-v1-1-4d6125048fb7@amd.com
Reviewed-by: Frank Li <Frank.Li@nxp.com>
Reviewed-by: Logan Gunthorpe <logang@deltatee.com>
Signed-off-by: Shivank Garg <shivankg@amd.com>
Link: https://patch.msgid.link/20260822-dmaengine-kref-fix-v5-3-d4a4ee47d927@amd.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>

1 files changed, 108 insertions, 0 deletions

diff --git a/samples/kprobes/kretprobe_example.c b/samples/kprobes/kretprobe_example.c
new file mode 100644
index 000000000..65d6dcafd
--- /dev/null
+++ b/samples/kprobes/kretprobe_example.c
@@ -0,0 +1,108 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * kretprobe_example.c
+ *
+ * Here's a sample kernel module showing the use of return probes to
+ * report the return value and total time taken for probed function
+ * to run.
+ *
+ * usage: insmod kretprobe_example.ko func=<func_name>
+ *
+ * If no func_name is specified, kernel_clone is instrumented
+ *
+ * For more information on theory of operation of kretprobes, see
+ * Documentation/trace/kprobes.rst
+ *
+ * Build and insert the kernel module as done in the kprobe example.
+ * You will see the trace data in /var/log/messages and on the console
+ * whenever the probed function returns. (Some messages may be suppressed
+ * if syslogd is configured to eliminate duplicate messages.)
+ */
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/kprobes.h>
+#include <linux/ktime.h>
+#include <linux/sched.h>
+
+static char func_name[KSYM_NAME_LEN] = "kernel_clone";
+module_param_string(func, func_name, KSYM_NAME_LEN, 0644);
+MODULE_PARM_DESC(func, "Function to kretprobe; this module will report the"
+			" function's execution time");
+
+/* per-instance private data */
+struct my_data {
+	ktime_t entry_stamp;
+};
+
+/* Here we use the entry_handler to timestamp function entry */
+static int entry_handler(struct kretprobe_instance *ri, struct pt_regs *regs)
+{
+	struct my_data *data;
+
+	if (!current->mm)
+		return 1;	/* Skip kernel threads */
+
+	data = (struct my_data *)ri->data;
+	data->entry_stamp = ktime_get();
+	return 0;
+}
+NOKPROBE_SYMBOL(entry_handler);
+
+/*
+ * Return-probe handler: Log the return value and duration. Duration may turn
+ * out to be zero consistently, depending upon the granularity of time
+ * accounting on the platform.
+ */
+static int ret_handler(struct kretprobe_instance *ri, struct pt_regs *regs)
+{
+	unsigned long retval = regs_return_value(regs);
+	struct my_data *data = (struct my_data *)ri->data;
+	s64 delta;
+	ktime_t now;
+
+	now = ktime_get();
+	delta = ktime_to_ns(ktime_sub(now, data->entry_stamp));
+	pr_info("%s returned %lu and took %lld ns to execute\n",
+			func_name, retval, (long long)delta);
+	return 0;
+}
+NOKPROBE_SYMBOL(ret_handler);
+
+static struct kretprobe my_kretprobe = {
+	.handler		= ret_handler,
+	.entry_handler		= entry_handler,
+	.data_size		= sizeof(struct my_data),
+	/* Probe up to 20 instances concurrently. */
+	.maxactive		= 20,
+};
+
+static int __init kretprobe_init(void)
+{
+	int ret;
+
+	my_kretprobe.kp.symbol_name = func_name;
+	ret = register_kretprobe(&my_kretprobe);
+	if (ret < 0) {
+		pr_err("register_kretprobe failed, returned %d\n", ret);
+		return ret;
+	}
+	pr_info("Planted return probe at %s: %p\n",
+			my_kretprobe.kp.symbol_name, my_kretprobe.kp.addr);
+	return 0;
+}
+
+static void __exit kretprobe_exit(void)
+{
+	unregister_kretprobe(&my_kretprobe);
+	pr_info("kretprobe at %p unregistered\n", my_kretprobe.kp.addr);
+
+	/* nmissed > 0 suggests that maxactive was set too low. */
+	pr_info("Missed probing %d instances of %s\n",
+		my_kretprobe.nmissed, my_kretprobe.kp.symbol_name);
+}
+
+module_init(kretprobe_init)
+module_exit(kretprobe_exit)
+MODULE_DESCRIPTION("sample kernel module showing the use of return probes");
+MODULE_LICENSE("GPL");