ftrace: Fix issue that 'direct->addr' not restored in modify_ftrace_direct()

Syzkaller report a WARNING: "WARN_ON(!direct)" in modify_ftrace_direct().

Root cause is 'direct->addr' was changed from 'old_addr' to 'new_addr' but
not restored if error happened on calling ftrace_modify_direct_caller().
Then it can no longer find 'direct' by that 'old_addr'.

To fix it, restore 'direct->addr' to 'old_addr' explicitly in error path.

Link: https://lore.kernel.org/linux-trace-kernel/[email protected]

Cc: [email protected]
Cc: <[email protected]>
Cc: <[email protected]>
Cc: <[email protected]>
Cc: <[email protected]>
Fixes: 8a141dd ("ftrace: Fix modify_ftrace_direct.")
Signed-off-by: Zheng Yejian <[email protected]>
Signed-off-by: Steven Rostedt (Google) <[email protected]>

Author: Zheng Yejian

kernel/trace/ftrace.c

@@ -5667,12 +5667,15 @@ int modify_ftrace_direct(unsigned long ip,
 		ret = 0;
 	}
 
-	if (unlikely(ret && new_direct)) {
-		direct->count++;
-		list_del_rcu(&new_direct->next);
-		synchronize_rcu_tasks();
-		kfree(new_direct);
-		ftrace_direct_func_count--;
+	if (ret) {
+		direct->addr = old_addr;
+		if (unlikely(new_direct)) {
+			direct->count++;
+			list_del_rcu(&new_direct->next);
+			synchronize_rcu_tasks();
+			kfree(new_direct);
+			ftrace_direct_func_count--;
+		}
 	}
 
  out_unlock: