gigaset: call module_put before restart of if_open()

if_open() calls try_module_get(), and after an attempt to lock a mutex
the if_open() function may return -ERESTARTSYS without
putting the module.  Then, when if_open() is executed again,
try_module_get() is called making the reference counter of THIS_MODULE
greater than one at successful exit from if_open().  The if_close()
function puts the module only once, and as a result it can't be
unloaded.

This patch adds module_put call before the return from if_open().

Found by Linux Driver Verification project (linuxtesting.org).

Signed-off-by: Pavel Shved <shved@ispras.ru>
Signed-off-by: David S. Miller <davem@conan.davemloft.net>

1 files changed, 3 insertions, 1 deletions

diff --git a/drivers/isdn/gigaset/interface.c b/drivers/isdn/gigaset/interface.c
index 59de638225fe..e35058bcd7b9 100644
--- a/drivers/isdn/gigaset/interface.c
+++ b/drivers/isdn/gigaset/interface.c
@@ -156,8 +156,10 @@ static int if_open(struct tty_struct *tty, struct file *filp)
         if (!cs || !try_module_get(cs->driver->owner))
                 return -ENODEV;
 
-        if (mutex_lock_interruptible(&cs->mutex))
+        if (mutex_lock_interruptible(&cs->mutex)) {
+                module_put(cs->driver->owner);
                 return -ERESTARTSYS;
+        }
         tty->driver_data = cs;
 
         ++cs->open_count;