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, 39 insertions, 0 deletions

diff --git a/drivers/rtc/rtc-generic.c b/drivers/rtc/rtc-generic.c
new file mode 100644
index 000000000..89ae78e93
--- /dev/null
+++ b/drivers/rtc/rtc-generic.c
@@ -0,0 +1,39 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/* rtc-generic: RTC driver using the generic RTC abstraction
+ *
+ * Copyright (C) 2008 Kyle McMartin <kyle@mcmartin.ca>
+ */
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/time.h>
+#include <linux/platform_device.h>
+#include <linux/rtc.h>
+
+static int __init generic_rtc_probe(struct platform_device *dev)
+{
+	struct rtc_device *rtc;
+	const struct rtc_class_ops *ops = dev_get_platdata(&dev->dev);
+
+	rtc = devm_rtc_device_register(&dev->dev, "rtc-generic",
+					ops, THIS_MODULE);
+	if (IS_ERR(rtc))
+		return PTR_ERR(rtc);
+
+	platform_set_drvdata(dev, rtc);
+
+	return 0;
+}
+
+static struct platform_driver generic_rtc_driver = {
+	.driver = {
+		.name = "rtc-generic",
+	},
+};
+
+module_platform_driver_probe(generic_rtc_driver, generic_rtc_probe);
+
+MODULE_AUTHOR("Kyle McMartin <kyle@mcmartin.ca>");
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("Generic RTC driver");
+MODULE_ALIAS("platform:rtc-generic");