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, 60 insertions, 0 deletions

diff --git a/drivers/rtc/rtc-starfire.c b/drivers/rtc/rtc-starfire.c
new file mode 100644
index 000000000..fbd1ed41c
--- /dev/null
+++ b/drivers/rtc/rtc-starfire.c
@@ -0,0 +1,60 @@
+/* rtc-starfire.c: Starfire platform RTC driver.
+ *
+ * Author: David S. Miller
+ * License: GPL
+ *
+ * Copyright (C) 2008 David S. Miller <davem@davemloft.net>
+ */
+
+#include <linux/kernel.h>
+#include <linux/init.h>
+#include <linux/rtc.h>
+#include <linux/platform_device.h>
+
+#include <asm/oplib.h>
+
+static u32 starfire_get_time(void)
+{
+	static char obp_gettod[32];
+	static u32 unix_tod;
+
+	sprintf(obp_gettod, "h# %08x unix-gettod",
+		(unsigned int) (long) &unix_tod);
+	prom_feval(obp_gettod);
+
+	return unix_tod;
+}
+
+static int starfire_read_time(struct device *dev, struct rtc_time *tm)
+{
+	rtc_time64_to_tm(starfire_get_time(), tm);
+	return 0;
+}
+
+static const struct rtc_class_ops starfire_rtc_ops = {
+	.read_time	= starfire_read_time,
+};
+
+static int __init starfire_rtc_probe(struct platform_device *pdev)
+{
+	struct rtc_device *rtc;
+
+	rtc = devm_rtc_allocate_device(&pdev->dev);
+	if (IS_ERR(rtc))
+		return PTR_ERR(rtc);
+
+	rtc->ops = &starfire_rtc_ops;
+	rtc->range_max = U32_MAX;
+
+	platform_set_drvdata(pdev, rtc);
+
+	return devm_rtc_register_device(rtc);
+}
+
+static struct platform_driver starfire_rtc_driver = {
+	.driver		= {
+		.name	= "rtc-starfire",
+	},
+};
+
+builtin_platform_driver_probe(starfire_rtc_driver, starfire_rtc_probe);