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, 67 insertions, 0 deletions

diff --git a/rust/syn/whitespace.rs b/rust/syn/whitespace.rs
new file mode 100644
index 000000000..b7319bd7a
--- /dev/null
+++ b/rust/syn/whitespace.rs
@@ -0,0 +1,67 @@
+// SPDX-License-Identifier: Apache-2.0 OR MIT
+
+pub(crate) fn skip(mut s: &str) -> &str {
+    'skip: while !s.is_empty() {
+        let byte = s.as_bytes()[0];
+        if byte == b'/' {
+            if s.starts_with("//")
+                && (!s.starts_with("///") || s.starts_with("////"))
+                && !s.starts_with("//!")
+            {
+                if let Some(i) = s.find('\n') {
+                    s = &s[i + 1..];
+                    continue;
+                } else {
+                    return "";
+                }
+            } else if s.starts_with("/**/") {
+                s = &s[4..];
+                continue;
+            } else if s.starts_with("/*")
+                && (!s.starts_with("/**") || s.starts_with("/***"))
+                && !s.starts_with("/*!")
+            {
+                let mut depth = 0;
+                let bytes = s.as_bytes();
+                let mut i = 0;
+                let upper = bytes.len() - 1;
+                while i < upper {
+                    if bytes[i] == b'/' && bytes[i + 1] == b'*' {
+                        depth += 1;
+                        i += 1; // eat '*'
+                    } else if bytes[i] == b'*' && bytes[i + 1] == b'/' {
+                        depth -= 1;
+                        if depth == 0 {
+                            s = &s[i + 2..];
+                            continue 'skip;
+                        }
+                        i += 1; // eat '/'
+                    }
+                    i += 1;
+                }
+                return s;
+            }
+        }
+        match byte {
+            b' ' | 0x09..=0x0D => {
+                s = &s[1..];
+                continue;
+            }
+            b if b <= 0x7F => {}
+            _ => {
+                let ch = s.chars().next().unwrap();
+                if is_whitespace(ch) {
+                    s = &s[ch.len_utf8()..];
+                    continue;
+                }
+            }
+        }
+        return s;
+    }
+    s
+}
+
+fn is_whitespace(ch: char) -> bool {
+    // Rust treats left-to-right mark and right-to-left mark as whitespace
+    ch.is_whitespace() || ch == '\u{200e}' || ch == '\u{200f}'
+}