Re: [PATCH] Input: uinput: Fix race condition on read()

[David Herrmann <dh.herrmann@xxxxxxxxxxxxxx>]

Hi Dmitry

On Mon, Mar 19, 2012 at 6:25 PM, Aristeu Rozanski
<aris@xxxxxxxxxxxxxxxxx> wrote:
> On Fri, Mar 16, 2012 at 09:04:29PM +0100, David Herrmann wrote:
>> Consider two threads calling read() on the same uinput-fd, both
>> non-blocking. Assume there is data-available so both will simultaneously
>> pass:
>>       udev->head == udev->tail
>> Then the first thread goes to sleep and the second one pops the message
>> from the queue. Now assume udev->head == udev->tail. If the first thread
>> wakes up it will call wait_event_*() and sleep in the waitq. This
>> effectively turns the non-blocking FD into a blocking one.
>>
>> We fix this by never calling wait_event_*() for non-blocking FDs hence we
>> will never sleep in the waitq here.
>>
>> Signed-off-by: David Herrmann <dh.herrmann@xxxxxxxxxxxxxx>
>> ---
>>  drivers/input/misc/uinput.c |   14 ++++++++------
>>  1 file changed, 8 insertions(+), 6 deletions(-)
>>
>> diff --git a/drivers/input/misc/uinput.c b/drivers/input/misc/uinput.c
>> index 7360568..1526814 100644
>> --- a/drivers/input/misc/uinput.c
>> +++ b/drivers/input/misc/uinput.c
>> @@ -460,13 +460,15 @@ static ssize_t uinput_read(struct file *file, char __user *buffer, size_t count,
>>       if (udev->state != UIST_CREATED)
>>               return -ENODEV;
>>
>> -     if (udev->head == udev->tail && (file->f_flags & O_NONBLOCK))
>> -             return -EAGAIN;
>> -
>> -     retval = wait_event_interruptible(udev->waitq,
>> +     if (file->f_flags & O_NONBLOCK) {
>> +             if (udev->head == udev->tail)
>> +                     return -EAGAIN;
>> +     } else {
>> +             retval = wait_event_interruptible(udev->waitq,
>>                       udev->head != udev->tail || udev->state != UIST_CREATED);
>> -     if (retval)
>> -             return retval;
>> +             if (retval)
>> +                     return retval;
>> +     }
>>
>>       retval = mutex_lock_interruptible(&udev->mutex);
>>       if (retval)
> makes sense, patch looks good
> Acked-by: Aristeu Rozanski <aris@xxxxxxxxx>

Ping (and the other uinput fix ;)).

Regards
David
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