Re: Patch for panic in n_tty_read()

[Stanislav Kozina <skozina@xxxxxxxxxx>]

Alan,

Thank you, updated fix (tested on bits based on commit 
bdc0077af574800d24318b6945cf2344e8dbb050) is attached.
Is this correct now?

Thanks and regards,
-Stanislav Kozina

> > You mean call to tty_put_user(), correct? Thanks for this catch.
> > So what about to unlock the lock for this time? Because we need to hold
> > the lock while checking tty->read_cnt in the while loop condition, correct?
> I think you are right on that yes.
>
> Alan

diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c
index ee1c268..54d1fc5 100644
--- a/drivers/tty/n_tty.c
+++ b/drivers/tty/n_tty.c
@@ -1832,13 +1832,13 @@ do_it_again:
 
 		if (tty->icanon && !L_EXTPROC(tty)) {
 			/* N.B. avoid overrun if nr == 0 */
+			spin_lock_irqsave(&tty->read_lock, flags);
 			while (nr && tty->read_cnt) {
 				int eol;
 
 				eol = test_and_clear_bit(tty->read_tail,
 						tty->read_flags);
 				c = tty->read_buf[tty->read_tail];
-				spin_lock_irqsave(&tty->read_lock, flags);
 				tty->read_tail = ((tty->read_tail+1) &
 						  (N_TTY_BUF_SIZE-1));
 				tty->read_cnt--;
@@ -1864,6 +1864,7 @@ do_it_again:
 					tty_audit_push(tty);
 					break;
 				}
+				spin_lock_irqsave(&tty->read_lock, flags);
 			}
 			if (retval)
 				break;