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, 23 insertions, 0 deletions

diff --git a/drivers/md/dm-vdo/string-utils.h b/drivers/md/dm-vdo/string-utils.h
new file mode 100644
index 000000000..96eecd38b
--- /dev/null
+++ b/drivers/md/dm-vdo/string-utils.h
@@ -0,0 +1,23 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright 2023 Red Hat
+ */
+
+#ifndef VDO_STRING_UTILS_H
+#define VDO_STRING_UTILS_H
+
+#include <linux/kernel.h>
+#include <linux/string.h>
+
+/* Utilities related to string manipulation */
+
+static inline const char *vdo_bool_to_string(bool value)
+{
+	return value ? "true" : "false";
+}
+
+/* Append a formatted string to the end of a buffer. */
+char *vdo_append_to_buffer(char *buffer, char *buf_end, const char *fmt, ...)
+	__printf(3, 4);
+
+#endif /* VDO_STRING_UTILS_H */