rust_binder: Implement BINDER_DEBUG_USER_ERROR for refcounting and death notifications

This adds dynamic debug logs for:
- Decrementing handle reference counts that are already zero.
- Mismatched reference states (calling inc_ref_done with no active
  inc_refs, or using a weak reference as a strong reference).
- Requesting or clearing death notifications on invalid references,
  already active notifications, or with mismatched cookies.

Reviewed-by: Carlos Llamas <cmllamas@google.com>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Signed-off-by: Jahnavi MN <jahnavimn@google.com>
Link: https://patch.msgid.link/20260716-rust_binder_debug_mask-v4-3-3d7436c2d2f2@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 6 insertions, 4 deletions

diff --git a/drivers/android/binder/node.rs b/drivers/android/binder/node.rs
index 59c5ab747bf4..fefa723d13c4 100644
--- a/drivers/android/binder/node.rs
+++ b/drivers/android/binder/node.rs
@@ -345,7 +345,7 @@ impl Node {
     ) -> Option<DLArc<Node>> {
         let inner = self.inner.access_mut(owner_inner);
         if inner.active_inc_refs == 0 {
-            pr_err!("inc_ref_done called when no active inc_refs");
+            binder_debug!(UserError, "inc_ref_done called when no active inc_refs");
             return None;
         }
 
@@ -821,6 +821,7 @@ impl NodeRef {
 
     pub(crate) fn clone(&self, strong: bool) -> Result<NodeRef> {
         if strong && self.strong_count == 0 {
+            binder_debug!(UserError, "tried to use weak ref as strong ref");
             return Err(EINVAL);
         }
         Ok(self
@@ -861,9 +862,10 @@ impl NodeRef {
             *count += 1;
         } else {
             if *count == 0 {
-                pr_warn!(
-                    "pid {} performed invalid decrement on ref\n",
-                    kernel::current!().pid()
+                binder_debug!(
+                    UserError,
+                    "performed invalid {} decrement on ref",
+                    if strong { "strong" } else { "weak" }
                 );
                 return false;
             }