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Commit 64325a3b authored by Ilya Zykov's avatar Ilya Zykov Committed by Greg Kroah-Hartman
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tty: Correct tty buffer flush. 



  The root of problem is carelessly zeroing pointer(in function __tty_buffer_flush()),
when another thread can use it. It can be cause of "NULL pointer dereference".
  Main idea of the patch, this is never free last (struct tty_buffer) in the active buffer.
Only flush the data for ldisc(buf->head->read = buf->head->commit).
At that moment driver can collect(write) data in buffer without conflict.
It is repeat behavior of flush_to_ldisc(), only without feeding data to ldisc.

Also revert:
  commit c56a00a1
  tty: hold lock across tty buffer finding and buffer filling
In order to delete the unneeded locks any more.

Signed-off-by: default avatarIlya Zykov <ilya@ilyx.ru>
CC: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent f8a2b220

drivers/tty/tty_buffer.c

+22 −70
Original line number Diff line number Diff line
@@ -119,11 +119,14 @@ static void __tty_buffer_flush(struct tty_port *port) 
	struct tty_bufhead *buf = &port->buf;

	struct tty_buffer *thead;



	while ((thead = buf->head) != NULL) {

		buf->head = thead->next;

		tty_buffer_free(port, thead);

	if (unlikely(buf->head == NULL))

		return;

	while ((thead = buf->head->next) != NULL) {

		tty_buffer_free(port, buf->head);

		buf->head = thead;

	}

	buf->tail = NULL;

	WARN_ON(buf->head != buf->tail);

	buf->head->read = buf->head->commit;

}



/**
@@ -194,19 +197,22 @@ static struct tty_buffer *tty_buffer_find(struct tty_port *port, size_t size) 
	   have queued and recycle that ? */

}

/**

 *	__tty_buffer_request_room		-	grow tty buffer if needed

 *	tty_buffer_request_room		-	grow tty buffer if needed

 *	@tty: tty structure

 *	@size: size desired

 *

 *	Make at least size bytes of linear space available for the tty

 *	buffer. If we fail return the size we managed to find.

 *      Locking: Caller must hold port->buf.lock

 *

 *	Locking: Takes port->buf.lock

 */

static int __tty_buffer_request_room(struct tty_port *port, size_t size)

int tty_buffer_request_room(struct tty_port *port, size_t size)

{

	struct tty_bufhead *buf = &port->buf;

	struct tty_buffer *b, *n;

	int left;

	unsigned long flags;

	spin_lock_irqsave(&buf->lock, flags);

	/* OPTIMISATION: We could keep a per tty "zero" sized buffer to

	   remove this conditional if its worth it. This would be invisible

	   to the callers */
@@ -228,31 +234,9 @@ static int __tty_buffer_request_room(struct tty_port *port, size_t size) 
		} else

			size = left;

	}



	spin_unlock_irqrestore(&buf->lock, flags);

	return size;

}





/**

 *	tty_buffer_request_room		-	grow tty buffer if needed

 *	@port: tty port structure

 *	@size: size desired

 *

 *	Make at least size bytes of linear space available for the tty

 *	buffer. If we fail return the size we managed to find.

 *

 *	Locking: Takes port->buf.lock

 */

int tty_buffer_request_room(struct tty_port *port, size_t size)

{

	unsigned long flags;

	int length;



	spin_lock_irqsave(&port->buf.lock, flags);

	length = __tty_buffer_request_room(port, size);

	spin_unlock_irqrestore(&port->buf.lock, flags);

	return length;

}

EXPORT_SYMBOL_GPL(tty_buffer_request_room);



/**
@@ -271,26 +255,18 @@ EXPORT_SYMBOL_GPL(tty_buffer_request_room); 
int tty_insert_flip_string_fixed_flag(struct tty_port *port,

		const unsigned char *chars, char flag, size_t size)

{

	struct tty_bufhead *buf = &port->buf;

	int copied = 0;

	do {

		int goal = min_t(size_t, size - copied, TTY_BUFFER_PAGE);

		int space;

		unsigned long flags;

		struct tty_buffer *tb;



		spin_lock_irqsave(&buf->lock, flags);

		space = __tty_buffer_request_room(port, goal);

		tb = buf->tail;

		int space = tty_buffer_request_room(port, goal);

		struct tty_buffer *tb = port->buf.tail;

		/* If there is no space then tb may be NULL */

		if (unlikely(space == 0)) {

			spin_unlock_irqrestore(&buf->lock, flags);

			break;

		}

		memcpy(tb->char_buf_ptr + tb->used, chars, space);

		memset(tb->flag_buf_ptr + tb->used, flag, space);

		tb->used += space;

		spin_unlock_irqrestore(&buf->lock, flags);

		copied += space;

		chars += space;

		/* There is a small chance that we need to split the data over
@@ -317,26 +293,18 @@ EXPORT_SYMBOL(tty_insert_flip_string_fixed_flag); 
int tty_insert_flip_string_flags(struct tty_port *port,

		const unsigned char *chars, const char *flags, size_t size)

{

	struct tty_bufhead *buf = &port->buf;

	int copied = 0;

	do {

		int goal = min_t(size_t, size - copied, TTY_BUFFER_PAGE);

		int space;

		unsigned long __flags;

		struct tty_buffer *tb;



		spin_lock_irqsave(&buf->lock, __flags);

		space = __tty_buffer_request_room(port, goal);

		tb = buf->tail;

		int space = tty_buffer_request_room(port, goal);

		struct tty_buffer *tb = port->buf.tail;

		/* If there is no space then tb may be NULL */

		if (unlikely(space == 0)) {

			spin_unlock_irqrestore(&buf->lock, __flags);

			break;

		}

		memcpy(tb->char_buf_ptr + tb->used, chars, space);

		memcpy(tb->flag_buf_ptr + tb->used, flags, space);

		tb->used += space;

		spin_unlock_irqrestore(&buf->lock, __flags);

		copied += space;

		chars += space;

		flags += space;
@@ -392,21 +360,13 @@ EXPORT_SYMBOL(tty_schedule_flip); 
int tty_prepare_flip_string(struct tty_port *port, unsigned char **chars,

		size_t size)

{

	struct tty_bufhead *buf = &port->buf;

	int space;

	unsigned long flags;

	struct tty_buffer *tb;



	spin_lock_irqsave(&buf->lock, flags);

	space = __tty_buffer_request_room(port, size);



	tb = buf->tail;

	int space = tty_buffer_request_room(port, size);

	if (likely(space)) {

		struct tty_buffer *tb = port->buf.tail;

		*chars = tb->char_buf_ptr + tb->used;

		memset(tb->flag_buf_ptr + tb->used, TTY_NORMAL, space);

		tb->used += space;

	}

	spin_unlock_irqrestore(&buf->lock, flags);

	return space;

}

EXPORT_SYMBOL_GPL(tty_prepare_flip_string);
@@ -430,21 +390,13 @@ EXPORT_SYMBOL_GPL(tty_prepare_flip_string); 
int tty_prepare_flip_string_flags(struct tty_port *port,

			unsigned char **chars, char **flags, size_t size)

{

	struct tty_bufhead *buf = &port->buf;

	int space;

	unsigned long __flags;

	struct tty_buffer *tb;



	spin_lock_irqsave(&buf->lock, __flags);

	space = __tty_buffer_request_room(port, size);



	tb = buf->tail;

	int space = tty_buffer_request_room(port, size);

	if (likely(space)) {

		struct tty_buffer *tb = port->buf.tail;

		*chars = tb->char_buf_ptr + tb->used;

		*flags = tb->flag_buf_ptr + tb->used;

		tb->used += space;

	}

	spin_unlock_irqrestore(&buf->lock, __flags);

	return space;

}

EXPORT_SYMBOL_GPL(tty_prepare_flip_string_flags);