linux-kernel - [PATCH] binder: fix potential UAF of target

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Message-Id: <20220517185817.598872-1-cmllamas@google.com>
Date:   Tue, 17 May 2022 18:58:17 +0000
From:   Carlos Llamas <cmllamas@...gle.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Arve Hjønnevåg" <arve@...roid.com>,
        Todd Kjos <tkjos@...roid.com>,
        Martijn Coenen <maco@...roid.com>,
        Christian Brauner <brauner@...nel.org>
Cc:     Joel Fernandes <joel@...lfernandes.org>,
        Hridya Valsaraju <hridya@...gle.com>,
        Suren Baghdasaryan <surenb@...gle.com>,
        kernel-team@...roid.com, linux-kernel@...r.kernel.org,
        Dan Carpenter <dan.carpenter@...cle.com>,
        Carlos Llamas <cmllamas@...gle.com>
Subject: [PATCH] binder: fix potential UAF of target_{proc,thread}

Commit 9474be34a727 ("binder: add failed transaction logging info")
dereferences target_{proc,thread} after they have been potentially
freed by binder_proc_dec_tmpref() and binder_thread_dec_tmpref().

This patch delays the release of the two references after their last
usage. Fixes the following two errors reported by smatch:

  drivers/android/binder.c:3562 binder_transaction() error: dereferencing freed memory 'target_proc'
  drivers/android/binder.c:3563 binder_transaction() error: dereferencing freed memory 'target_thread'

Fixes: 9474be34a727 ("binder: add failed transaction logging info")
Reported-by: Dan Carpenter <dan.carpenter@...cle.com>
Signed-off-by: Carlos Llamas <cmllamas@...gle.com>
---
 drivers/android/binder.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/drivers/android/binder.c b/drivers/android/binder.c
index d9253b2a7bd9..83facfa1a5c3 100644
--- a/drivers/android/binder.c
+++ b/drivers/android/binder.c
@@ -3546,10 +3546,6 @@ static void binder_transaction(struct binder_proc *proc,
 err_empty_call_stack:
 err_dead_binder:
 err_invalid_target_handle:
-	if (target_thread)
-		binder_thread_dec_tmpref(target_thread);
-	if (target_proc)
-		binder_proc_dec_tmpref(target_proc);
 	if (target_node) {
 		binder_dec_node(target_node, 1, 0);
 		binder_dec_node_tmpref(target_node);
@@ -3565,6 +3561,11 @@ static void binder_transaction(struct binder_proc *proc,
 		     (u64)tr->data_size, (u64)tr->offsets_size,
 		     return_error_line);
 
+	if (target_thread)
+		binder_thread_dec_tmpref(target_thread);
+	if (target_proc)
+		binder_proc_dec_tmpref(target_proc);
+
 	{
 		struct binder_transaction_log_entry *fe;
 
-- 
2.36.0.550.gb090851708-goog