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, 60 insertions, 0 deletions

diff --git a/rust/macros/helpers.rs b/rust/macros/helpers.rs
new file mode 100644
index 000000000..d18fbf4da
--- /dev/null
+++ b/rust/macros/helpers.rs
@@ -0,0 +1,60 @@
+// SPDX-License-Identifier: GPL-2.0
+
+use proc_macro2::TokenStream;
+use quote::ToTokens;
+use syn::{
+    parse::{
+        Parse,
+        ParseStream, //
+    },
+    Attribute,
+    Error,
+    LitStr,
+    Result, //
+};
+
+/// A string literal that is required to have ASCII value only.
+pub(crate) struct AsciiLitStr(LitStr);
+
+impl Parse for AsciiLitStr {
+    fn parse(input: ParseStream<'_>) -> Result<Self> {
+        let s: LitStr = input.parse()?;
+        if !s.value().is_ascii() {
+            return Err(Error::new_spanned(s, "expected ASCII-only string literal"));
+        }
+        Ok(Self(s))
+    }
+}
+
+impl ToTokens for AsciiLitStr {
+    fn to_tokens(&self, ts: &mut TokenStream) {
+        self.0.to_tokens(ts);
+    }
+}
+
+impl AsciiLitStr {
+    pub(crate) fn value(&self) -> String {
+        self.0.value()
+    }
+}
+
+pub(crate) fn file() -> String {
+    #[cfg(not(CONFIG_RUSTC_HAS_SPAN_FILE))]
+    {
+        proc_macro::Span::call_site()
+            .source_file()
+            .path()
+            .to_string_lossy()
+            .into_owned()
+    }
+
+    #[cfg(CONFIG_RUSTC_HAS_SPAN_FILE)]
+    {
+        proc_macro::Span::call_site().file()
+    }
+}
+
+/// Obtain all `#[cfg]` attributes.
+pub(crate) fn gather_cfg_attrs(attr: &[Attribute]) -> impl Iterator<Item = &Attribute> + '_ {
+    attr.iter().filter(|a| a.path().is_ident("cfg"))
+}