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, 28 insertions, 0 deletions

diff --git a/rust/helpers/page.c b/rust/helpers/page.c
new file mode 100644
index 000000000..f8463fbed
--- /dev/null
+++ b/rust/helpers/page.c
@@ -0,0 +1,28 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/gfp.h>
+#include <linux/highmem.h>
+#include <linux/mm.h>
+
+__rust_helper struct page *rust_helper_alloc_pages(gfp_t gfp_mask,
+						   unsigned int order)
+{
+	return alloc_pages(gfp_mask, order);
+}
+
+__rust_helper void *rust_helper_kmap_local_page(struct page *page)
+{
+	return kmap_local_page(page);
+}
+
+__rust_helper void rust_helper_kunmap_local(const void *addr)
+{
+	kunmap_local(addr);
+}
+
+#ifndef NODE_NOT_IN_PAGE_FLAGS
+__rust_helper int rust_helper_page_to_nid(const struct page *page)
+{
+	return page_to_nid(page);
+}
+#endif