exec: Add node tampering blacklist function

We'll be adding checks to block writes from processes which tamper with
values that we control from within the kernel, especially ones that
userspace writes to for boosting. Add a central function to perform the
process check to reduce code duplication.

This blacklists the following processes which are known to tamper with
such values:
  Binder

Signed-off-by: Danny Lin <danny@kdrag0n.dev>

include/linux/binfmts.h

@@ -152,4 +152,12 @@ extern int do_execveat(int, struct filename *,
 		       int);
 int do_execve_file(struct file *file, void *__argv, void *__envp);
 
+static inline bool task_is_booster(struct task_struct *tsk)
+{
+	char comm[sizeof(tsk->comm)];
+
+	get_task_comm(comm, tsk);
+	return !memcmp(comm, "Binder", 6);
+}
+
 #endif /* _LINUX_BINFMTS_H */