Gitweb:
http://git.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=42fd552e8647316757ded0176466c41d17934dcf
Commit: 42fd552e8647316757ded0176466c41d17934dcf
Parent: f8a745942b1b7f052cb76bb8a893d12cb6329c84
Author: Alan Cox <[EMAIL PROTECTED]>
AuthorDate: Fri Aug 10 13:01:05 2007 -0700
Committer: Linus Torvalds <[EMAIL PROTECTED]>
CommitDate: Sat Aug 11 15:47:41 2007 -0700
fix serial buffer memory leak
Patch c5c34d4862e18ef07c1276d233507f540fb5a532 (tty: flush flip buffer on
ldisc input queue flush) introduces a race condition which can lead to
memory
leaks.
The problem can be triggered when tcflush() is called when data are being
pushed to the line discipline driver by flush_to_ldisc().
flush_to_ldisc() releases tty->buf.lock when calling the line discipline
receive_buf function. At that poing tty_buffer_flush() kicks in and sets
both
tty->buf.head and tty->buf.tail to NULL. When flush_to_ldisc() finishes, it
restores tty->buf.head but doesn't touch tty->buf.tail. This corrups the
buffer queue, and the next call to tty_buffer_request_room() will allocate a
new buffer and overwrite tty->buf.head. The previous buffer is then lost
forever without being released.
(Thanks to Laurent for the above text, for finding, disgnosing and reporting
the bug)
- Use tty->flags bits for the flush status.
- Wait for the flag to clear again before returning
- Fix the doc error noted
- Fix flush of empty queue leaving stale flushpending
[EMAIL PROTECTED]: cleanup]
Signed-off-by: Alan Cox <[EMAIL PROTECTED]>
Acked-by: Paul Fulghum <[EMAIL PROTECTED]>
Cc: Laurent Pinchart <[EMAIL PROTECTED]>
Signed-off-by: Andrew Morton <[EMAIL PROTECTED]>
Signed-off-by: Linus Torvalds <[EMAIL PROTECTED]>
---
drivers/char/tty_io.c | 56 +++++++++++++++++++++++++++++++++++++++++++-----
include/linux/tty.h | 2 +
2 files changed, 52 insertions(+), 6 deletions(-)
diff --git a/drivers/char/tty_io.c b/drivers/char/tty_io.c
index de37ebc..51ea93c 100644
--- a/drivers/char/tty_io.c
+++ b/drivers/char/tty_io.c
@@ -369,25 +369,54 @@ static void tty_buffer_free(struct tty_struct *tty,
struct tty_buffer *b)
}
/**
- * tty_buffer_flush - flush full tty buffers
+ * __tty_buffer_flush - flush full tty buffers
* @tty: tty to flush
*
- * flush all the buffers containing receive data
+ * flush all the buffers containing receive data. Caller must
+ * hold the buffer lock and must have ensured no parallel flush to
+ * ldisc is running.
*
- * Locking: none
+ * Locking: Caller must hold tty->buf.lock
*/
-static void tty_buffer_flush(struct tty_struct *tty)
+static void __tty_buffer_flush(struct tty_struct *tty)
{
struct tty_buffer *thead;
- unsigned long flags;
- spin_lock_irqsave(&tty->buf.lock, flags);
while((thead = tty->buf.head) != NULL) {
tty->buf.head = thead->next;
tty_buffer_free(tty, thead);
}
tty->buf.tail = NULL;
+}
+
+/**
+ * tty_buffer_flush - flush full tty buffers
+ * @tty: tty to flush
+ *
+ * flush all the buffers containing receive data. If the buffer is
+ * being processed by flush_to_ldisc then we defer the processing
+ * to that function
+ *
+ * Locking: none
+ */
+
+static void tty_buffer_flush(struct tty_struct *tty)
+{
+ unsigned long flags;
+ spin_lock_irqsave(&tty->buf.lock, flags);
+
+ /* If the data is being pushed to the tty layer then we can't
+ process it here. Instead set a flag and the flush_to_ldisc
+ path will process the flush request before it exits */
+ if (test_bit(TTY_FLUSHING, &tty->flags)) {
+ set_bit(TTY_FLUSHPENDING, &tty->flags);
+ spin_unlock_irqrestore(&tty->buf.lock, flags);
+ wait_event(tty->read_wait,
+ test_bit(TTY_FLUSHPENDING, &tty->flags) == 0);
+ return;
+ } else
+ __tty_buffer_flush(tty);
spin_unlock_irqrestore(&tty->buf.lock, flags);
}
@@ -3594,6 +3623,7 @@ static void flush_to_ldisc(struct work_struct *work)
return;
spin_lock_irqsave(&tty->buf.lock, flags);
+ set_bit(TTY_FLUSHING, &tty->flags); /* So we know a flush is
running */
head = tty->buf.head;
if (head != NULL) {
tty->buf.head = NULL;
@@ -3607,6 +3637,11 @@ static void flush_to_ldisc(struct work_struct *work)
tty_buffer_free(tty, tbuf);
continue;
}
+ /* Ldisc or user is trying to flush the buffers
+ we are feeding to the ldisc, stop feeding the
+ line discipline as we want to empty the queue */
+ if (test_bit(TTY_FLUSHPENDING, &tty->flags))
+ break;
if (!tty->receive_room) {
schedule_delayed_work(&tty->buf.work, 1);
break;
@@ -3620,8 +3655,17 @@ static void flush_to_ldisc(struct work_struct *work)
disc->receive_buf(tty, char_buf, flag_buf, count);
spin_lock_irqsave(&tty->buf.lock, flags);
}
+ /* Restore the queue head */
tty->buf.head = head;
}
+ /* We may have a deferred request to flush the input buffer,
+ if so pull the chain under the lock and empty the queue */
+ if (test_bit(TTY_FLUSHPENDING, &tty->flags)) {
+ __tty_buffer_flush(tty);
+ clear_bit(TTY_FLUSHPENDING, &tty->flags);
+ wake_up(&tty->read_wait);
+ }
+ clear_bit(TTY_FLUSHING, &tty->flags);
spin_unlock_irqrestore(&tty->buf.lock, flags);
tty_ldisc_deref(disc);
diff --git a/include/linux/tty.h b/include/linux/tty.h
index 691a174..6570719 100644
--- a/include/linux/tty.h
+++ b/include/linux/tty.h
@@ -274,6 +274,8 @@ struct tty_struct {
#define TTY_PTY_LOCK 16 /* pty private */
#define TTY_NO_WRITE_SPLIT 17 /* Preserve write boundaries to driver
*/
#define TTY_HUPPED 18 /* Post driver->hangup() */
+#define TTY_FLUSHING 19 /* Flushing to ldisc in progress */
+#define TTY_FLUSHPENDING 20 /* Queued buffer flush pending */
#define TTY_WRITE_FLUSH(tty) tty_write_flush((tty))
-
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