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, 56 insertions, 0 deletions

diff --git a/samples/rust/rust_minimal.rs b/samples/rust/rust_minimal.rs
new file mode 100644
index 000000000..8c910d314
--- /dev/null
+++ b/samples/rust/rust_minimal.rs
@@ -0,0 +1,56 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Rust minimal sample.
+
+use kernel::prelude::*;
+
+module! {
+    type: RustMinimal,
+    name: "rust_minimal",
+    authors: ["Rust for Linux Contributors"],
+    description: "Rust minimal sample",
+    license: "GPL",
+    params: {
+        test_parameter: i64 {
+            default: 1,
+            description: "This parameter has a default of 1",
+        },
+        test_bool_parameter: bool {
+            default: false,
+            description: "This boolean parameter defaults to false",
+        },
+    },
+}
+
+struct RustMinimal {
+    numbers: KVec<i32>,
+}
+
+impl kernel::Module for RustMinimal {
+    fn init(_module: &'static ThisModule) -> Result<Self> {
+        pr_info!("Rust minimal sample (init)\n");
+        pr_info!("Am I built-in? {}\n", !cfg!(MODULE));
+        pr_info!(
+            "test_parameter: {}\n",
+            module_parameters::test_parameter.value()
+        );
+        pr_info!(
+            "test_bool_parameter: {}\n",
+            module_parameters::test_bool_parameter.value()
+        );
+
+        let mut numbers = KVec::new();
+        numbers.push(72, GFP_KERNEL)?;
+        numbers.push(108, GFP_KERNEL)?;
+        numbers.push(200, GFP_KERNEL)?;
+
+        Ok(RustMinimal { numbers })
+    }
+}
+
+impl Drop for RustMinimal {
+    fn drop(&mut self) {
+        pr_info!("My numbers are {:?}\n", self.numbers);
+        pr_info!("Rust minimal sample (exit)\n");
+    }
+}