Re: Possible race in loop.ko

[Ming Lei]

On Fri, Jul 28, 2017 at 11:55 PM, Anton Volkov <avolkov@xxxxxxxxx> wrote:
> Hello.
> While searching for races in Linux kernel I've come across
> drivers/block/loop.ko module. Here is the question that I came up with while
> analyzing results. Lines are given using the info from Linux v4.12.
>
> In loop_init function additional initialization happens after a successful
> call to misc_register() (loop.c: line 1961). Consider the following case:
>
> Thread 1:                 Thread 2:
> loop_init()
>   misc_register()         loop_control_ioctl
>   part_shift = 0          -> loop_add
>   if (max_part > 0) {          alloc_disk(1 << part_shift)
>     part_shift =
>          <greater than 0>
>     ...
>   }
>
> In this case alloc_disk() will be called with 1 as a parameter although
> part_shift should have been greater than 0. Maybe it would be better to move
> the call to a misc_register() function a bit further down (at least so it
> could be after the part_shift initialization)?

That looks a good idea, could you cook a patch to do it?


-- 
Ming Lei