Re: [PATCH V2 3/6] mpcore_wdt: Fix WDIOC_SETOPTIONS handling

Russell King - ARM Linux
2011-07-06T13:48:48Z

On Tue, Jul 05, 2011 at 11:00:37PM +0400, Vitaly Kuzmichev wrote:
> According to the include/linux/watchdog.h WDIOC_SETOPTIONS is
> classified as 'read from device' ioctl call:
> #define WDIOC_SETOPTIONS _IOR(WATCHDOG_IOCTL_BASE, 4, int)
>
> However, the driver 'mpcore_wdt' performs 'copy_from_user' only if
> _IOC_WRITE is set, thus the local variable 'uarg' which is used in
> WDIOC_SETOPTIONS handling remains uninitialized.
>
> The proper way to fix this is to bind WDIOC_SETOPTIONS to _IOW,
> but this will break compatibility.
> So adding additional condition for performing 'copy_from_user'.

That looks like something which needs fixing in watchdog land. And it's
not too difficult:

1. Change the existing WDIOC_SETOPTIONS to WDIOC_SETOPTIONS_OLD
2. Add a new, correctly defined WDIOC_SETOPTIONS.
3. Update all drivers to use WDIOC_SETOPTIONS.
4. Provide a helper which deals with WDIOC_SETOPTIONS_OLD and translates
it to the proper WDIOC_SETOPTIONS call (this could be just:

if (cmd == WDIOC_SETOPTIONS_OLD) {
static int first = 1;
if (first)
pr_warn("%s:%d used old WDIOC_SETOPTIONS call. Please rebuild\n",
current->comm, current->pid);
first = 0;
cmd = WDIOC_SETOPTIONS;
}

before any argument copies.

This means you preserve existing compatibility with userspace, yet gain
a path to a non-broken ioctl interface.

As stuff gets rebuilt and replaced, you'll eventually be able to remove
the above. That period used to be two years for such simple changes.