Enable write to /proc/PID/last_siginfo (delivers signal)

Author: igorcanadi

fs/proc/base.c

@@ -1145,13 +1145,8 @@ static int wait_waitsignal(struct task_struct *task, unsigned long long mask) {
 
 if (mask & (1ULL << PROCTRACE_START_TASK)) {
 // deliver signal to the child
-// TODO: add semantics to disable delivery
-
-if (task->last_siginfo) {
+if (task->last_siginfo && !task->exit_code) {
 task->exit_code = task->last_siginfo->si_signo;
-printk("PROCTRACE sinal sent to the task: %d", task->exit_code);
-} else {
-printk("PROCTRACE no signal to send\n");
 }
 
 wake_up_process(task);
@@ -1287,8 +1282,27 @@ static ssize_t last_siginfo_read(struct file *file, char __user *buf,
 return length;
 }
 
+/*
+ * On zero write, don't deliver signal to the child.
+ * On non-zero write, deliver the specified signal
+ */
+static ssize_t last_siginfo_write(struct file *file,
+const unsigned char __user *buf, size_t count, loff_t *ppos) {
+
+struct task_struct *task = get_proc_task(file->f_path.dentry->d_inode);
+
+task->last_siginfo = NULL;
+if (count > 1) {
+task->exit_code = *buf;
+return 1;
+}
+
+return 0;
+}
+
 static const struct file_operations proc_last_siginfo_operations = {
 .read= last_siginfo_read,
+.write= last_siginfo_write,
 };
 
 static ssize_t environ_read(struct file *file, char __user *buf,