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Commit d5698c28 authored by Christoph Hellwig's avatar Christoph Hellwig Committed by Linus Torvalds
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[PATCH] tty: cleanup release_mem 



release_mem contains two copies of exactly the same code.  Refactor these
into a new helper, release_tty.  The only change in behaviour is that the
driver reference count is now decremented after the master tty has been
freed instead of before.

[penberg@cs.helsinki.fi: fix use-after-free in release_tty.]
Cc: Alan Cox <alan@redhat.com>
Signed-off-by: default avatarChristoph Hellwig <hch@lst.de>
Signed-off-by: default avatarPekka Enberg <penberg@cs.helsinki.fi>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 4b98d11b

drivers/char/tty_io.c

+37 −36
Original line number Diff line number Diff line
@@ -154,7 +154,7 @@ static int tty_release(struct inode *, struct file *); 
int tty_ioctl(struct inode * inode, struct file * file,

	      unsigned int cmd, unsigned long arg);

static int tty_fasync(int fd, struct file * filp, int on);

static void release_mem(struct tty_struct *tty, int idx);

static void release_tty(struct tty_struct *tty, int idx);



/**

 *	alloc_tty_struct	-	allocate a tty object
@@ -2002,7 +2002,7 @@ static int init_dev(struct tty_driver *driver, int idx, 


	/* 

	 * All structures have been allocated, so now we install them.

	 * Failures after this point use release_mem to clean up, so 

	 * Failures after this point use release_tty to clean up, so

	 * there's no need to null out the local pointers.

	 */

	if (!(driver->flags & TTY_DRIVER_DEVPTS_MEM)) {
@@ -2023,8 +2023,8 @@ static int init_dev(struct tty_driver *driver, int idx, 


	/* 

	 * Structures all installed ... call the ldisc open routines.

	 * If we fail here just call release_mem to clean up.  No need

	 * to decrement the use counts, as release_mem doesn't care.

	 * If we fail here just call release_tty to clean up.  No need

	 * to decrement the use counts, as release_tty doesn't care.

	 */



	if (tty->ldisc.open) {
@@ -2094,17 +2094,17 @@ static int init_dev(struct tty_driver *driver, int idx, 
	retval = -ENOMEM;

	goto end_init;



	/* call the tty release_mem routine to clean out this slot */

	/* call the tty release_tty routine to clean out this slot */

release_mem_out:

	if (printk_ratelimit())

		printk(KERN_INFO "init_dev: ldisc open failed, "

				 "clearing slot %d\n", idx);

	release_mem(tty, idx);

	release_tty(tty, idx);

	goto end_init;

}



/**

 *	release_mem		-	release tty structure memory

 *	release_one_tty		-	release tty structure memory

 *

 *	Releases memory associated with a tty structure, and clears out the

 *	driver table slots. This function is called when a device is no longer
@@ -2116,37 +2116,14 @@ static int init_dev(struct tty_driver *driver, int idx, 
 *	of ttys that the driver keeps.

 *		FIXME: should we require tty_mutex is held here ??

 */



static void release_mem(struct tty_struct *tty, int idx)

static void release_one_tty(struct tty_struct *tty, int idx)

{

	struct tty_struct *o_tty;

	struct ktermios *tp;

	int devpts = tty->driver->flags & TTY_DRIVER_DEVPTS_MEM;



	if ((o_tty = tty->link) != NULL) {

		if (!devpts)

			o_tty->driver->ttys[idx] = NULL;

		if (o_tty->driver->flags & TTY_DRIVER_RESET_TERMIOS) {

			tp = o_tty->termios;

			if (!devpts)

				o_tty->driver->termios[idx] = NULL;

			kfree(tp);



			tp = o_tty->termios_locked;

			if (!devpts)

				o_tty->driver->termios_locked[idx] = NULL;

			kfree(tp);

		}

		o_tty->magic = 0;

		o_tty->driver->refcount--;

		file_list_lock();

		list_del_init(&o_tty->tty_files);

		file_list_unlock();

		free_tty_struct(o_tty);

	}

	struct ktermios *tp;



	if (!devpts)

		tty->driver->ttys[idx] = NULL;



	if (tty->driver->flags & TTY_DRIVER_RESET_TERMIOS) {

		tp = tty->termios;

		if (!devpts)
@@ -2159,15 +2136,39 @@ static void release_mem(struct tty_struct *tty, int idx) 
		kfree(tp);

	}





	tty->magic = 0;

	tty->driver->refcount--;



	file_list_lock();

	list_del_init(&tty->tty_files);

	file_list_unlock();

	module_put(tty->driver->owner);



	free_tty_struct(tty);

}



/**

 *	release_tty		-	release tty structure memory

 *

 *	Release both @tty and a possible linked partner (think pty pair),

 *	and decrement the refcount of the backing module.

 *

 *	Locking:

 *		tty_mutex - sometimes only

 *		takes the file list lock internally when working on the list

 *	of ttys that the driver keeps.

 *		FIXME: should we require tty_mutex is held here ??

 */

static void release_tty(struct tty_struct *tty, int idx)

{

	struct tty_driver *driver = tty->driver;



	if (tty->link)

		release_one_tty(tty->link, idx);

	release_one_tty(tty, idx);

	module_put(driver->owner);

}



/*

 * Even releasing the tty structures is a tricky business.. We have

 * to be very careful that the structures are all released at the
@@ -2435,10 +2436,10 @@ static void release_dev(struct file * filp) 
		tty_set_termios_ldisc(o_tty,N_TTY); 

	}

	/*

	 * The release_mem function takes care of the details of clearing

	 * The release_tty function takes care of the details of clearing

	 * the slots and preserving the termios structure.

	 */

	release_mem(tty, idx);

	release_tty(tty, idx);



#ifdef CONFIG_UNIX98_PTYS

	/* Make this pty number available for reallocation */