tty: Remove dead termiox code

set_termiox() and the TCGETX handler bail out with -EINVAL immediately
if ->termiox is NULL, but there are no code paths that can set
->termiox to a non-NULL pointer; and no such code paths seem to have
existed since the termiox mechanism was introduced back in
commit 1d65b4a088de ("tty: Add termiox") in v2.6.28.
Similarly, no driver actually implements .set_termiox; and it looks like
no driver ever has.

Delete this dead code; but leave the definition of struct termiox in the
UAPI headers intact.

Signed-off-by: Jann Horn <jannh@google.com>
Link: https://lore.kernel.org/r/20201203020331.2394754-1-jannh@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/tty_ioctl.c

@@ -443,51 +443,6 @@ static int get_termio(struct tty_struct *tty, struct termio __user *termio)
 	return 0;
 }
 
-
-#ifdef TCGETX
-
-/**
- *	set_termiox	-	set termiox fields if possible
- *	@tty: terminal
- *	@arg: termiox structure from user
- *	@opt: option flags for ioctl type
- *
- *	Implement the device calling points for the SYS5 termiox ioctl
- *	interface in Linux
- */
-
-static int set_termiox(struct tty_struct *tty, void __user *arg, int opt)
-{
-	struct termiox tnew;
-	struct tty_ldisc *ld;
-
-	if (tty->termiox == NULL)
-		return -EINVAL;
-	if (copy_from_user(&tnew, arg, sizeof(struct termiox)))
-		return -EFAULT;
-
-	ld = tty_ldisc_ref(tty);
-	if (ld != NULL) {
-		if ((opt & TERMIOS_FLUSH) && ld->ops->flush_buffer)
-			ld->ops->flush_buffer(tty);
-		tty_ldisc_deref(ld);
-	}
-	if (opt & TERMIOS_WAIT) {
-		tty_wait_until_sent(tty, 0);
-		if (signal_pending(current))
-			return -ERESTARTSYS;
-	}
-
-	down_write(&tty->termios_rwsem);
-	if (tty->ops->set_termiox)
-		tty->ops->set_termiox(tty, &tnew);
-	up_write(&tty->termios_rwsem);
-	return 0;
-}
-
-#endif
-
-
 #ifdef TIOCGETP
 /*
  * These are deprecated, but there is limited support..
@@ -815,23 +770,11 @@ int tty_mode_ioctl(struct tty_struct *tty, struct file *file,
 		return ret;
 #endif
 #ifdef TCGETX
-	case TCGETX: {
+	case TCGETX:
-		struct termiox ktermx;
-		if (real_tty->termiox == NULL)
-			return -EINVAL;
-		down_read(&real_tty->termios_rwsem);
-		memcpy(&ktermx, real_tty->termiox, sizeof(struct termiox));
-		up_read(&real_tty->termios_rwsem);
-		if (copy_to_user(p, &ktermx, sizeof(struct termiox)))
-			ret = -EFAULT;
-		return ret;
-	}
 	case TCSETX:
-		return set_termiox(real_tty, p, 0);
 	case TCSETXW:
-		return set_termiox(real_tty, p, TERMIOS_WAIT);
 	case TCSETXF:
-		return set_termiox(real_tty, p, TERMIOS_FLUSH);
+		return -EINVAL;
 #endif		
 	case TIOCGSOFTCAR:
 		copy_termios(real_tty, &kterm);

include/linux/tty.h

@@ -303,7 +303,6 @@ struct tty_struct {
 	spinlock_t flow_lock;
 	/* Termios values are protected by the termios rwsem */
 	struct ktermios termios, termios_locked;
-	struct termiox *termiox;	/* May be NULL for unsupported */
 	char name[64];
 	struct pid *pgrp;		/* Protected by ctrl lock */
 	struct pid *session;

include/linux/tty_driver.h

@@ -224,14 +224,6 @@
  *	line). See tty_do_resize() if you need to wrap the standard method
  *	in your own logic - the usual case.
  *
- * void (*set_termiox)(struct tty_struct *tty, struct termiox *new);
- *
- *	Called when the device receives a termiox based ioctl. Passes down
- *	the requested data from user space. This method will not be invoked
- *	unless the tty also has a valid tty->termiox pointer.
- *
- *	Optional: Called under the termios lock
- *
  * int (*get_icount)(struct tty_struct *tty, struct serial_icounter *icount);
  *
  *	Called when the device receives a TIOCGICOUNT ioctl. Passed a kernel
@@ -285,7 +277,6 @@ struct tty_operations {
 	int (*tiocmset)(struct tty_struct *tty,
 			unsigned int set, unsigned int clear);
 	int (*resize)(struct tty_struct *tty, struct winsize *ws);
-	int (*set_termiox)(struct tty_struct *tty, struct termiox *tnew);
 	int (*get_icount)(struct tty_struct *tty,
 				struct serial_icounter_struct *icount);
 	int  (*get_serial)(struct tty_struct *tty, struct serial_struct *p);