tty: Drop krefs for interrupted tty lock

commit e9036d0662360cd4c79578565ce422ed5872f301 upstream.

When the tty lock is interrupted on attempted re-open, 2 tty krefs
are still held. Drop extra kref before returning failure from
tty_lock_interruptible(), and drop lookup kref before returning
failure from tty_open().

Fixes: 0bfd464d3fdd ("tty: Wait interruptibly for tty lock on reopen")
Reported-by: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Cc: Jiri Slaby <jslaby@suse.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
index 7cef543..1bb629a 100644 (file)
--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -2070,13 +2070,12 @@ retry_open:
                if (tty) {
                        mutex_unlock(&tty_mutex);
                        retval = tty_lock_interruptible(tty);
+                       tty_kref_put(tty);  /* drop kref from tty_driver_lookup_tty() */
                        if (retval) {
                                if (retval == -EINTR)
                                        retval = -ERESTARTSYS;
                                goto err_unref;
                        }
-                       /* safe to drop the kref from tty_driver_lookup_tty() */
-                       tty_kref_put(tty);
                        retval = tty_reopen(tty);
                        if (retval < 0) {
                                tty_unlock(tty);

diff --git a/drivers/tty/tty_mutex.c b/drivers/tty/tty_mutex.c
index d09293b..cff304a 100644 (file)
--- a/drivers/tty/tty_mutex.c
+++ b/drivers/tty/tty_mutex.c
@@ -24,10 +24,15 @@ EXPORT_SYMBOL(tty_lock);
 
 int tty_lock_interruptible(struct tty_struct *tty)
 {
+       int ret;
+
        if (WARN(tty->magic != TTY_MAGIC, "L Bad %p\n", tty))
                return -EIO;
        tty_kref_get(tty);
-       return mutex_lock_interruptible(&tty->legacy_mutex);
+       ret = mutex_lock_interruptible(&tty->legacy_mutex);
+       if (ret)
+               tty_kref_put(tty);
+       return ret;
 }
 
 void __lockfunc tty_unlock(struct tty_struct *tty)