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Commit c56a00a1 authored by Xiaobing Tu's avatar Xiaobing Tu Committed by Greg Kroah-Hartman
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tty: hold lock across tty buffer finding and buffer filling 



tty_buffer_request_room is well protected, but while after it returns,
 it releases the port->lock. tty->buf.tail might be modified
by either irq handler or other threads. The patch adds more protection
by holding the lock across tty buffer finding and buffer filling.

Signed-off-by: default avatarAlek Du <alek.du@intel.com>
Signed-off-by: default avatarXiaobing Tu <xiaobing.tu@intel.com>
Cc: Jiri Slaby <jslaby@suse.cz>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 871bdea6

drivers/tty/tty_buffer.c

+65 −20
Original line number Diff line number Diff line
@@ -185,25 +185,19 @@ static struct tty_buffer *tty_buffer_find(struct tty_struct *tty, size_t size) 
	/* Should possibly check if this fails for the largest buffer we

	   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: Takes tty->buf.lock

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

 */

int tty_buffer_request_room(struct tty_struct *tty, size_t size)

static int __tty_buffer_request_room(struct tty_struct *tty, size_t size)

{

	struct tty_buffer *b, *n;

	int left;

	unsigned long flags;



	spin_lock_irqsave(&tty->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 */
@@ -225,9 +219,30 @@ int tty_buffer_request_room(struct tty_struct *tty, size_t size) 
			size = left;

	}



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

	return size;

}





/**

 *	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: Takes tty->buf.lock

 */

int tty_buffer_request_room(struct tty_struct *tty, size_t size)

{

	unsigned long flags;

	int length;



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

	length = __tty_buffer_request_room(tty, size);

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

	return length;

}

EXPORT_SYMBOL_GPL(tty_buffer_request_room);



/**
@@ -249,14 +264,22 @@ int tty_insert_flip_string_fixed_flag(struct tty_struct *tty, 
	int copied = 0;

	do {

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

		int space = tty_buffer_request_room(tty, goal);

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

		int space;

		unsigned long flags;

		struct tty_buffer *tb;



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

		space = __tty_buffer_request_room(tty, goal);

		tb = tty->buf.tail;

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

		if (unlikely(space == 0))

		if (unlikely(space == 0)) {

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

		copied += space;

		chars += space;

		/* There is a small chance that we need to split the data over
@@ -286,14 +309,22 @@ int tty_insert_flip_string_flags(struct tty_struct *tty, 
	int copied = 0;

	do {

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

		int space = tty_buffer_request_room(tty, goal);

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

		int space;

		unsigned long __flags;

		struct tty_buffer *tb;



		spin_lock_irqsave(&tty->buf.lock, __flags);

		space = __tty_buffer_request_room(tty, goal);

		tb = tty->buf.tail;

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

		if (unlikely(space == 0))

		if (unlikely(space == 0)) {

			spin_unlock_irqrestore(&tty->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(&tty->buf.lock, __flags);

		copied += space;

		chars += space;

		flags += space;
@@ -344,13 +375,20 @@ EXPORT_SYMBOL(tty_schedule_flip); 
int tty_prepare_flip_string(struct tty_struct *tty, unsigned char **chars,

								size_t size)

{

	int space = tty_buffer_request_room(tty, size);

	int space;

	unsigned long flags;

	struct tty_buffer *tb;



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

	space = __tty_buffer_request_room(tty, size);



	tb = tty->buf.tail;

	if (likely(space)) {

		struct tty_buffer *tb = tty->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(&tty->buf.lock, flags);

	return space;

}

EXPORT_SYMBOL_GPL(tty_prepare_flip_string);
@@ -374,13 +412,20 @@ EXPORT_SYMBOL_GPL(tty_prepare_flip_string); 
int tty_prepare_flip_string_flags(struct tty_struct *tty,

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

{

	int space = tty_buffer_request_room(tty, size);

	int space;

	unsigned long __flags;

	struct tty_buffer *tb;



	spin_lock_irqsave(&tty->buf.lock, __flags);

	space = __tty_buffer_request_room(tty, size);



	tb = tty->buf.tail;

	if (likely(space)) {

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

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

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

		tb->used += space;

	}

	spin_unlock_irqrestore(&tty->buf.lock, __flags);

	return space;

}

EXPORT_SYMBOL_GPL(tty_prepare_flip_string_flags);