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, 69 insertions, 0 deletions

diff --git a/rust/helpers/bitops.c b/rust/helpers/bitops.c
new file mode 100644
index 000000000..271b8a712
--- /dev/null
+++ b/rust/helpers/bitops.c
@@ -0,0 +1,69 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/bitops.h>
+#include <linux/find.h>
+
+__rust_helper
+void rust_helper___set_bit(unsigned long nr, unsigned long *addr)
+{
+	__set_bit(nr, addr);
+}
+
+__rust_helper
+void rust_helper___clear_bit(unsigned long nr, unsigned long *addr)
+{
+	__clear_bit(nr, addr);
+}
+
+__rust_helper
+void rust_helper_set_bit(unsigned long nr, volatile unsigned long *addr)
+{
+	set_bit(nr, addr);
+}
+
+__rust_helper
+void rust_helper_clear_bit(unsigned long nr, volatile unsigned long *addr)
+{
+	clear_bit(nr, addr);
+}
+
+/*
+ * The rust_helper_ prefix is intentionally omitted below so that the
+ * declarations in include/linux/find.h are compatible with these helpers.
+ *
+ * Note that the below #ifdefs mean that the helper is only created if C does
+ * not provide a definition.
+ */
+#ifdef find_first_zero_bit
+__rust_helper
+unsigned long _find_first_zero_bit(const unsigned long *p, unsigned long size)
+{
+	return find_first_zero_bit(p, size);
+}
+#endif /* find_first_zero_bit */
+
+#ifdef find_next_zero_bit
+__rust_helper
+unsigned long _find_next_zero_bit(const unsigned long *addr,
+				  unsigned long size, unsigned long offset)
+{
+	return find_next_zero_bit(addr, size, offset);
+}
+#endif /* find_next_zero_bit */
+
+#ifdef find_first_bit
+__rust_helper
+unsigned long _find_first_bit(const unsigned long *addr, unsigned long size)
+{
+	return find_first_bit(addr, size);
+}
+#endif /* find_first_bit */
+
+#ifdef find_next_bit
+__rust_helper
+unsigned long _find_next_bit(const unsigned long *addr, unsigned long size,
+			     unsigned long offset)
+{
+	return find_next_bit(addr, size, offset);
+}
+#endif /* find_next_bit */