tty: Fix unsafe vt paste_selection()
Convert the tty_buffer_flush() exclusion mechanism to a
public interface - tty_buffer_lock/unlock_exclusive() - and use
the interface to safely write the paste selection to the line
discipline.
Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/drivers/tty/tty_buffer.c b/drivers/tty/tty_buffer.c
index dbe4a71..f22e116 100644
--- a/drivers/tty/tty_buffer.c
+++ b/drivers/tty/tty_buffer.c
@@ -30,6 +30,42 @@
/**
+ * tty_buffer_lock_exclusive - gain exclusive access to buffer
+ * tty_buffer_unlock_exclusive - release exclusive access
+ *
+ * @port - tty_port owning the flip buffer
+ *
+ * Guarantees safe use of the line discipline's receive_buf() method by
+ * excluding the buffer work and any pending flush from using the flip
+ * buffer. Data can continue to be added concurrently to the flip buffer
+ * from the driver side.
+ *
+ * On release, the buffer work is restarted if there is data in the
+ * flip buffer
+ */
+
+void tty_buffer_lock_exclusive(struct tty_port *port)
+{
+ struct tty_bufhead *buf = &port->buf;
+
+ atomic_inc(&buf->priority);
+ mutex_lock(&buf->lock);
+}
+
+void tty_buffer_unlock_exclusive(struct tty_port *port)
+{
+ struct tty_bufhead *buf = &port->buf;
+ int restart;
+
+ restart = buf->head->commit != buf->head->read;
+
+ atomic_dec(&buf->priority);
+ mutex_unlock(&buf->lock);
+ if (restart)
+ queue_work(system_unbound_wq, &buf->work);
+}
+
+/**
* tty_buffer_space_avail - return unused buffer space
* @port - tty_port owning the flip buffer
*
@@ -158,7 +194,7 @@
* being processed by flush_to_ldisc then we defer the processing
* to that function
*
- * Locking: takes flush_mutex to ensure single-threaded flip buffer
+ * Locking: takes buffer lock to ensure single-threaded flip buffer
* 'consumer'
*/
@@ -168,16 +204,16 @@
struct tty_bufhead *buf = &port->buf;
struct tty_buffer *next;
- buf->flushpending = 1;
+ atomic_inc(&buf->priority);
- mutex_lock(&buf->flush_mutex);
+ mutex_lock(&buf->lock);
while ((next = buf->head->next) != NULL) {
tty_buffer_free(port, buf->head);
buf->head = next;
}
buf->head->read = buf->head->commit;
- buf->flushpending = 0;
- mutex_unlock(&buf->flush_mutex);
+ atomic_dec(&buf->priority);
+ mutex_unlock(&buf->lock);
}
/**
@@ -383,7 +419,7 @@
*
* The receive_buf method is single threaded for each tty instance.
*
- * Locking: takes flush_mutex to ensure single-threaded flip buffer
+ * Locking: takes buffer lock to ensure single-threaded flip buffer
* 'consumer'
*/
@@ -402,14 +438,14 @@
if (disc == NULL)
return;
- mutex_lock(&buf->flush_mutex);
+ mutex_lock(&buf->lock);
while (1) {
struct tty_buffer *head = buf->head;
int count;
- /* Ldisc or user is trying to flush the buffers. */
- if (buf->flushpending)
+ /* Ldisc or user is trying to gain exclusive access */
+ if (atomic_read(&buf->priority))
break;
count = head->commit - head->read;
@@ -426,7 +462,7 @@
break;
}
- mutex_unlock(&buf->flush_mutex);
+ mutex_unlock(&buf->lock);
tty_ldisc_deref(disc);
}
@@ -482,13 +518,12 @@
{
struct tty_bufhead *buf = &port->buf;
- mutex_init(&buf->flush_mutex);
+ mutex_init(&buf->lock);
tty_buffer_reset(&buf->sentinel, 0);
buf->head = &buf->sentinel;
buf->tail = &buf->sentinel;
init_llist_head(&buf->free);
atomic_set(&buf->memory_used, 0);
- buf->flushpending = 0;
+ atomic_set(&buf->priority, 0);
INIT_WORK(&buf->work, flush_to_ldisc);
}
-