Audit: Log TIOCSTI

AUDIT_TTY records currently log all data read by processes marked for
TTY input auditing, even if the data was "pushed back" using the TIOCSTI
ioctl, not typed by the user.

This patch records all TIOCSTI calls to disambiguate the input. It
generates one audit message per character pushed back; considering
TIOCSTI is used very rarely, this simple solution is probably good
enough. (The only program I could find that uses TIOCSTI is mailx/nail
in "header editing" mode, e.g. using the ~h escape. mailx is used very
rarely, and the escapes are used even rarer.)

Signed-Off-By: Miloslav Trmac <[e-mail]>
Signed-off-by: Al Viro <[e-mail]>
Signed-off-by: James Morris <[e-mail]>

drivers/char/tty_audit.c

···
 		tty_audit_buf_free(buf);
 }
 
+static void tty_audit_log(const char *description, struct task_struct *tsk,
+			  uid_t loginuid, unsigned sessionid, int major,
+			  int minor, unsigned char *data, size_t size)
+{
+	struct audit_buffer *ab;
+
+	ab = audit_log_start(NULL, GFP_KERNEL, AUDIT_TTY);
+	if (ab) {
+		char name[sizeof(tsk->comm)];
+		uid_t uid = task_uid(tsk);
+
+		audit_log_format(ab, "%s pid=%u uid=%u auid=%u ses=%u "
+				 "major=%d minor=%d comm=", description,
+				 tsk->pid, uid, loginuid, sessionid,
+				 major, minor);
+		get_task_comm(name, tsk);
+		audit_log_untrustedstring(ab, name);
+		audit_log_format(ab, " data=");
+		audit_log_n_hex(ab, data, size);
+		audit_log_end(ab);
+	}
+}
+
 /**
  *	tty_audit_buf_push	-	Push buffered data out
  *
···
 			       unsigned int sessionid,
 			       struct tty_audit_buf *buf)
 {
-	struct audit_buffer *ab;
-
 	if (buf->valid == 0)
 		return;
 	if (audit_enabled == 0)
 		return;
-	ab = audit_log_start(NULL, GFP_KERNEL, AUDIT_TTY);
-	if (ab) {
-		char name[sizeof(tsk->comm)];
-		uid_t uid = task_uid(tsk);
-
-		audit_log_format(ab, "tty pid=%u uid=%u auid=%u ses=%u "
-				 "major=%d minor=%d comm=",
-				 tsk->pid, uid, loginuid, sessionid,
-				 buf->major, buf->minor);
-		get_task_comm(name, tsk);
-		audit_log_untrustedstring(ab, name);
-		audit_log_format(ab, " data=");
-		audit_log_n_hex(ab, buf->data, buf->valid);
-		audit_log_end(ab);
-	}
+	tty_audit_log("tty", tsk, loginuid, sessionid, buf->major, buf->minor,
+		      buf->data, buf->valid);
 	buf->valid = 0;
 }
 
···
 	sig->audit_tty = current->signal->audit_tty;
 	spin_unlock_irq(&current->sighand->siglock);
 	sig->tty_audit_buf = NULL;
+}
+
+/**
+ *	tty_audit_tiocsti	-	Log TIOCSTI
+ */
+void tty_audit_tiocsti(struct tty_struct *tty, char ch)
+{
+	struct tty_audit_buf *buf;
+	int major, minor, should_audit;
+
+	spin_lock_irq(&current->sighand->siglock);
+	should_audit = current->signal->audit_tty;
+	buf = current->signal->tty_audit_buf;
+	if (buf)
+		atomic_inc(&buf->count);
+	spin_unlock_irq(&current->sighand->siglock);
+
+	major = tty->driver->major;
+	minor = tty->driver->minor_start + tty->index;
+	if (buf) {
+		mutex_lock(&buf->mutex);
+		if (buf->major == major && buf->minor == minor)
+			tty_audit_buf_push_current(buf);
+		mutex_unlock(&buf->mutex);
+		tty_audit_buf_put(buf);
+	}
+
+	if (should_audit && audit_enabled) {
+		uid_t auid;
+		unsigned int sessionid;
+
+		auid = audit_get_loginuid(current);
+		sessionid = audit_get_sessionid(current);
+		tty_audit_log("ioctl=TIOCSTI", current, auid, sessionid, major,
+			      minor, &ch, 1);
+	}
 }
 
 /**

drivers/char/tty_io.c

···
 		return -EPERM;
 	if (get_user(ch, p))
 		return -EFAULT;
+	tty_audit_tiocsti(tty, ch);
 	ld = tty_ldisc_ref_wait(tty);
 	ld->ops->receive_buf(tty, &ch, &mbz, 1);
 	tty_ldisc_deref(ld);

include/linux/tty.h

···
 			       size_t size);
 extern void tty_audit_exit(void);
 extern void tty_audit_fork(struct signal_struct *sig);
+extern void tty_audit_tiocsti(struct tty_struct *tty, char ch);
 extern void tty_audit_push(struct tty_struct *tty);
 extern void tty_audit_push_task(struct task_struct *tsk,
 					uid_t loginuid, u32 sessionid);
 #else
 static inline void tty_audit_add_data(struct tty_struct *tty,
 				      unsigned char *data, size_t size)
+{
+}
+static inline void tty_audit_tiocsti(struct tty_struct *tty, char ch)
 {
 }
 static inline void tty_audit_exit(void)