On Tue, May 5, 2009 at 1:12 PM, Pavel Machek <pavel@xxxxxx> wrote:
> Hi!
>
>> Add a misc device, "suspend_blocker", that allows user-space processes
>> to block auto suspend. The device has ioctls to create a suspend_blocker,
>> and to block and unblock suspend. To delete the suspend_blocker, close
>> the device.
>
> Rafael proposed write() interface. I don't think you answered that.
>
I think an ioctl interface makes more sense. With a write interface
you either have to do string parsing, or invent some other protocol
between the driver and user-space.
>
>> +static int create_user_suspend_blocker(struct file *file, void __user *name,
>> + size_t name_len)
>> +{
>> + struct user_suspend_blocker *bl;
>> + if (file->private_data)
>> + return -EBUSY;
>> + bl = kzalloc(sizeof(*bl) + name_len + 1, GFP_KERNEL);
>> + if (!bl)
>> + return -ENOMEM;
>> + if (copy_from_user(bl->name, name, name_len))
>> + goto err_fault;
>> + suspend_blocker_init(&bl->blocker, bl->name);
>> + file->private_data = bl;
>> + return 0;
>
> kzalloc on user-supplied argument. Sounds like bad idea.
>
> Aha. And probably integer overflow in the same line. Ouch.
>
The size is limited to _IOC_SIZEMASK with is 13 or 14 bits depending
on the architecture. Do you want a lower limit on the name length?
> Plus you actually 'trust' the string from userspace. Someone passes
> "evdev" there and can masquerade as a part of kernel.
Yes. I could add a prefix to userspace names, but it did not seem
worth the effort since the name is not used as a key for anything.
>
>> +static int user_suspend_blocker_release(struct inode *inode, struct file *file)
>> +{
>> + struct user_suspend_blocker *bl = file->private_data;
>> + if (!bl)
>> + return 0;
>> + suspend_blocker_destroy(&bl->blocker);
>> + kfree(bl);
>> + return 0;
>> +}
>
> What happens if someone does dup() on such file descriptor?
>
Then you have two file descriptors pointing to the same suspend
blocker. Release is called when the last reference goes away.
--
Arve Hjønnevåg
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