[PATCH] TIOCCONS fix

This fixes the TIOCCONS race; it's the same as the 2.4 patch except for
a fix for a brown-paperbag bug in it.

drivers/char/tty_io.c

@@ -132,12 +132,6 @@ extern struct tty_driver pts_driver;	/* Unix98 pty slaves;  for /dev/ptmx */
 
 extern void disable_early_printk(void);
 
-/*
- * redirect is the pseudo-tty that console output
- * is redirected to if asked by TIOCCONS.
- */
-static struct tty_struct *redirect;
-
 static void initialize_tty_struct(struct tty_struct *tty);
 
 static ssize_t tty_read(struct file *, char *, size_t, loff_t *);
@@ -400,6 +394,8 @@ static struct file_operations hung_up_tty_fops = {
 	.release	= tty_release,
 };
 
+static spinlock_t redirect_lock = SPIN_LOCK_UNLOCKED;
+static struct file *redirect;
 /*
  * This can be called by the "eventd" kernel thread.  That is process synchronous,
  * but doesn't hold any locks, so we need to make sure we have the appropriate
@@ -409,7 +405,7 @@ void do_tty_hangup(void *data)
 {
 	struct tty_struct *tty = (struct tty_struct *) data;
 	struct file * cons_filp = NULL;
-	struct file *filp;
+	struct file *filp, *f = NULL;
 	struct task_struct *p;
 	struct pid *pid;
 	int    closecount = 0, n;
@@ -419,6 +415,15 @@ void do_tty_hangup(void *data)
 
 	/* inuse_filps is protected by the single kernel lock */
 	lock_kernel();
+
+	spin_lock(&redirect_lock);
+	if (redirect && redirect->private_data == tty) {
+		f = redirect;
+		redirect = NULL;
+	}
+	spin_unlock(&redirect_lock);
+	if (f)
+		fput(f);
 	
 	check_tty_count(tty, "do_tty_hangup");
 	file_list_lock();
@@ -726,39 +731,40 @@ static ssize_t tty_write(struct file * file, const char * buf, size_t count,
 {
 	int is_console;
 	struct tty_struct * tty;
-	struct inode *inode;
-
-	/* Can't seek (pwrite) on ttys.  */
-	if (ppos != &file->f_pos)
-		return -ESPIPE;
-
+	struct inode *inode = file->f_dentry->d_inode;
 	/*
 	 *      For now, we redirect writes from /dev/console as
 	 *      well as /dev/tty0.
 	 */
-	inode = file->f_dentry->d_inode;
 	is_console = IS_SYSCONS_DEV(inode->i_rdev) ||
 		     IS_CONSOLE_DEV(inode->i_rdev);
 
-	if (is_console && redirect)
-		tty = redirect;
-	else
-		tty = (struct tty_struct *)file->private_data;
+	/* Can't seek (pwrite) on ttys.  */
+	if (ppos != &file->f_pos)
+		return -ESPIPE;
+
+	if (is_console) {
+		struct file *p = NULL;
+
+		spin_lock(&redirect_lock);
+		if (redirect) {
+			get_file(redirect);
+			p = redirect;
+		}
+		spin_unlock(&redirect_lock);
+
+		if (p) {
+			ssize_t res = vfs_write(p, buf, count, &p->f_pos);
+			fput(p);
+			return res;
+		}
+	}
+
+	tty = (struct tty_struct *)file->private_data;
 	if (tty_paranoia_check(tty, inode->i_rdev, "tty_write"))
 		return -EIO;
 	if (!tty || !tty->driver->write || (test_bit(TTY_IO_ERROR, &tty->flags)))
 		return -EIO;
-#if 0
-	if (!is_console && L_TOSTOP(tty) && (tty->pgrp > 0) &&
-	    (current->tty == tty) && (tty->pgrp != current->pgrp)) {
-		if (is_orphaned_pgrp(current->pgrp))
-			return -EIO;
-		if (!is_ignored(SIGTTOU)) {
-			(void) kill_pg(current->pgrp, SIGTTOU, 1);
-			return -ERESTARTSYS;
-		}
-	}
-#endif
 	if (!tty->ldisc.write)
 		return -EIO;
 	return do_tty_write(tty->ldisc.write, tty, file,
@@ -1221,7 +1227,7 @@ static void release_dev(struct file * filp)
 	/*
 	 * If _either_ side is closing, make sure there aren't any
 	 * processes that still think tty or o_tty is their controlling
-	 * tty.  Also, clear redirect if it points to either tty.
+	 * tty.
 	 */
 	if (tty_closing || o_tty_closing) {
 		struct task_struct *p;
@@ -1235,9 +1241,6 @@ static void release_dev(struct file * filp)
 			for_each_task_pid(o_tty->session, PIDTYPE_SID, p,l, pid)
 				p->tty = NULL;
 		read_unlock(&tasklist_lock);
-
-		if (redirect == tty || (o_tty && redirect == o_tty))
-			redirect = NULL;
 	}
 
 	/* check whether both sides are closing ... */
@@ -1526,19 +1529,29 @@ static int tiocswinsz(struct tty_struct *tty, struct tty_struct *real_tty,
 	return 0;
 }
 
-static int tioccons(struct inode *inode,
-	struct tty_struct *tty, struct tty_struct *real_tty)
+static int tioccons(struct inode *inode, struct file *file)
 {
 	if (IS_SYSCONS_DEV(inode->i_rdev) ||
 	    IS_CONSOLE_DEV(inode->i_rdev)) {
+		struct file *f;
 		if (!capable(CAP_SYS_ADMIN))
 			return -EPERM;
+		spin_lock(&redirect_lock);
+		f = redirect;
 		redirect = NULL;
+		spin_unlock(&redirect_lock);
+		if (f)
+			fput(f);
 		return 0;
 	}
-	if (redirect)
+	spin_lock(&redirect_lock);
+	if (redirect) {
+		spin_unlock(&redirect_lock);
 		return -EBUSY;
-	redirect = real_tty;
+	}
+	get_file(file);
+	redirect = file;
+	spin_unlock(&redirect_lock);
 	return 0;
 }
 
@@ -1786,7 +1799,7 @@ int tty_ioctl(struct inode * inode, struct file * file,
 		case TIOCSWINSZ:
 			return tiocswinsz(tty, real_tty, (struct winsize *) arg);
 		case TIOCCONS:
-			return tioccons(inode, tty, real_tty);
+			return real_tty!=tty ? -EINVAL : tioccons(inode, file);
 		case FIONBIO:
 			return fionbio(file, (int *) arg);
 		case TIOCEXCL:

include/linux/tty.h

@@ -345,7 +345,6 @@ struct tty_struct {
 extern void tty_write_flush(struct tty_struct *);
 
 extern struct termios tty_std_termios;
-extern struct tty_struct * redirect;
 extern struct tty_ldisc ldiscs[];
 extern int fg_console, last_console, want_console;