rust_binder: fix oneway spam detection

commit 4fc87c240b8f30e22b7ebaae29d57105589e1c0b upstream.

The spam detection logic in TreeRange was executed before the current
request was inserted into the tree. So the new request was not being
factored in the spam calculation. Fix this by moving the logic after
the new range has been inserted.

Also, the detection logic for ArrayRange was missing altogether which
meant large spamming transactions could get away without being detected.
Fix this by implementing an equivalent low_oneway_space() in ArrayRange.

Note that I looked into centralizing this logic in RangeAllocator but
iterating through 'state' and 'size' got a bit too complicated (for me)
and I abandoned this effort.

Cc: stable <stable@kernel.org>
Cc: Alice Ryhl <aliceryhl@google.com>
Fixes: eafedbc7c050 ("rust_binder: add Rust Binder driver")
Signed-off-by: Carlos Llamas <cmllamas@google.com>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Link: https://patch.msgid.link/20260210232949.3770644-1-cmllamas@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 9 insertions, 9 deletions

diff --git a/drivers/android/binder/range_alloc/tree.rs b/drivers/android/binder/range_alloc/tree.rs
index 7b1a248fcb02..27c451f73614 100644
--- a/drivers/android/binder/range_alloc/tree.rs
+++ b/drivers/android/binder/range_alloc/tree.rs
@@ -164,15 +164,6 @@ impl<T> TreeRangeAllocator<T> {
             self.free_oneway_space
         };
 
-        // Start detecting spammers once we have less than 20%
-        // of async space left (which is less than 10% of total
-        // buffer size).
-        //
-        // (This will short-circut, so `low_oneway_space` is
-        // only called when necessary.)
-        let oneway_spam_detected =
-            is_oneway && new_oneway_space < self.size / 10 && self.low_oneway_space(pid);
-
         let (found_size, found_off, tree_node, free_tree_node) = match self.find_best_match(size) {
             None => {
                 pr_warn!("ENOSPC from range_alloc.reserve_new - size: {}", size);
@@ -203,6 +194,15 @@ impl<T> TreeRangeAllocator<T> {
             self.free_tree.insert(free_tree_node);
         }
 
+        // Start detecting spammers once we have less than 20%
+        // of async space left (which is less than 10% of total
+        // buffer size).
+        //
+        // (This will short-circuit, so `low_oneway_space` is
+        // only called when necessary.)
+        let oneway_spam_detected =
+            is_oneway && new_oneway_space < self.size / 10 && self.low_oneway_space(pid);
+
         Ok((found_off, oneway_spam_detected))
     }