tty_register_driver: only allocate tty instances when defined

If device->num is zero we attempt to kmalloc() zero bytes.  When SLUB is
enabled this returns a null pointer and take that as an allocation failure
and fail the device register.  Check for no devices and avoid the
allocation.

[akpm: opportunistic kzalloc() conversion]
Signed-off-by: Andy Whitcroft <apw@shadowen.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 2 insertions, 3 deletions

diff --git a/drivers/char/tty_io.c b/drivers/char/tty_io.c
index 7a32df59490..389da364e6b 100644
--- a/drivers/char/tty_io.c
+++ b/drivers/char/tty_io.c
@@ -3720,11 +3720,10 @@ int tty_register_driver(struct tty_driver *driver)
         if (driver->flags & TTY_DRIVER_INSTALLED)
                 return 0;
 
-        if (!(driver->flags & TTY_DRIVER_DEVPTS_MEM)) {
-                p = kmalloc(driver->num * 3 * sizeof(void *), GFP_KERNEL);
+        if (!(driver->flags & TTY_DRIVER_DEVPTS_MEM) && driver->num) {
+                p = kzalloc(driver->num * 3 * sizeof(void *), GFP_KERNEL);
                 if (!p)
                         return -ENOMEM;
-                memset(p, 0, driver->num * 3 * sizeof(void *));
         }
 
         if (!driver->major) {