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, 62 insertions, 0 deletions

diff --git a/lib/kunit/string-stream.h b/lib/kunit/string-stream.h
new file mode 100644
index 000000000..7be2450c7
--- /dev/null
+++ b/lib/kunit/string-stream.h
@@ -0,0 +1,62 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * C++ stream style string builder used in KUnit for building messages.
+ *
+ * Copyright (C) 2019, Google LLC.
+ * Author: Brendan Higgins <brendanhiggins@google.com>
+ */
+
+#ifndef _KUNIT_STRING_STREAM_H
+#define _KUNIT_STRING_STREAM_H
+
+#include <linux/spinlock.h>
+#include <linux/types.h>
+#include <linux/stdarg.h>
+
+struct string_stream_fragment {
+	struct list_head node;
+	char *fragment;
+};
+
+struct string_stream {
+	size_t length;
+	struct list_head fragments;
+	/* length and fragments are protected by this lock */
+	spinlock_t lock;
+	gfp_t gfp;
+	bool append_newlines;
+};
+
+struct kunit;
+
+struct string_stream *kunit_alloc_string_stream(struct kunit *test, gfp_t gfp);
+void kunit_free_string_stream(struct kunit *test, struct string_stream *stream);
+
+struct string_stream *alloc_string_stream(gfp_t gfp);
+void free_string_stream(struct string_stream *stream);
+
+int __printf(2, 3) string_stream_add(struct string_stream *stream,
+				     const char *fmt, ...);
+
+int __printf(2, 0) string_stream_vadd(struct string_stream *stream,
+				      const char *fmt,
+				      va_list args);
+
+void string_stream_clear(struct string_stream *stream);
+
+char *string_stream_get_string(struct string_stream *stream);
+
+int string_stream_append(struct string_stream *stream,
+			 struct string_stream *other);
+
+bool string_stream_is_empty(struct string_stream *stream);
+
+void string_stream_destroy(struct string_stream *stream);
+
+static inline void string_stream_set_append_newlines(struct string_stream *stream,
+						     bool append_newlines)
+{
+	stream->append_newlines = append_newlines;
+}
+
+#endif /* _KUNIT_STRING_STREAM_H */