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Date: Mon, 15 Apr 2013 11:26:06 -0400
From: Peter Hurley <peter@...leysoftware.com>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Jiri Slaby <jslaby@...e.cz>, linux-serial@...r.kernel.org,
linux-kernel@...r.kernel.org,
Peter Hurley <peter@...leysoftware.com>
Subject: [PATCH 15/16] 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@...leysoftware.com>
---
drivers/tty/tty_buffer.c | 61 ++++++++++++++++++++++++++++++++++++----------
drivers/tty/vt/selection.c | 4 ++-
include/linux/tty.h | 4 +--
include/linux/tty_flip.h | 3 +++
4 files changed, 56 insertions(+), 16 deletions(-)
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 @@ static void tty_buffer_free(struct tty_port *port, struct tty_buffer *b)
* 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 @@ void tty_buffer_flush(struct tty_struct *tty)
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 @@ receive_buf(struct tty_struct *tty, struct tty_buffer *head, int count)
*
* 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 @@ static void flush_to_ldisc(struct work_struct *work)
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 @@ static void flush_to_ldisc(struct work_struct *work)
break;
}
- mutex_unlock(&buf->flush_mutex);
+ mutex_unlock(&buf->lock);
tty_ldisc_deref(disc);
}
@@ -482,13 +518,12 @@ void tty_buffer_init(struct tty_port *port)
{
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);
}
-
diff --git a/drivers/tty/vt/selection.c b/drivers/tty/vt/selection.c
index 2ca8d6b..ea27804 100644
--- a/drivers/tty/vt/selection.c
+++ b/drivers/tty/vt/selection.c
@@ -24,6 +24,7 @@
#include <linux/selection.h>
#include <linux/tiocl.h>
#include <linux/console.h>
+#include <linux/tty_flip.h>
/* Don't take this from <ctype.h>: 011-015 on the screen aren't spaces */
#define isspace(c) ((c) == ' ')
@@ -346,8 +347,8 @@ int paste_selection(struct tty_struct *tty)
console_unlock();
ld = tty_ldisc_ref_wait(tty);
+ tty_buffer_lock_exclusive(&vc->port);
- /* FIXME: this is completely unsafe */
add_wait_queue(&vc->paste_wait, &wait);
while (sel_buffer && sel_buffer_lth > pasted) {
set_current_state(TASK_INTERRUPTIBLE);
@@ -363,6 +364,7 @@ int paste_selection(struct tty_struct *tty)
remove_wait_queue(&vc->paste_wait, &wait);
__set_current_state(TASK_RUNNING);
+ tty_buffer_unlock_exclusive(&vc->port);
tty_ldisc_deref(ld);
return 0;
}
diff --git a/include/linux/tty.h b/include/linux/tty.h
index 2b880c2..0959a7b 100644
--- a/include/linux/tty.h
+++ b/include/linux/tty.h
@@ -67,8 +67,8 @@ static inline char *flag_buf_ptr(struct tty_buffer *b, int ofs)
struct tty_bufhead {
struct tty_buffer *head; /* Queue head */
struct work_struct work;
- struct mutex flush_mutex;
- unsigned int flushpending:1;
+ struct mutex lock;
+ atomic_t priority;
struct tty_buffer sentinel;
struct llist_head free; /* Free queue head */
atomic_t memory_used; /* In-use buffers excluding free list */
diff --git a/include/linux/tty_flip.h b/include/linux/tty_flip.h
index 6944ed2..21ddd7d 100644
--- a/include/linux/tty_flip.h
+++ b/include/linux/tty_flip.h
@@ -32,4 +32,7 @@ static inline int tty_insert_flip_string(struct tty_port *port,
return tty_insert_flip_string_fixed_flag(port, chars, TTY_NORMAL, size);
}
+extern void tty_buffer_lock_exclusive(struct tty_port *port);
+extern void tty_buffer_unlock_exclusive(struct tty_port *port);
+
#endif /* _LINUX_TTY_FLIP_H */
--
1.8.1.2
--
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