Re: [PATCH 1/3] nbd: del_gendisk after we cleanup the queue

On Fri, Apr 13, 2018 at 04:16:18PM +0000, Bart Van Assche wrote:

On Fri, 2018-04-13 at 12:03 -0400, Josef Bacik wrote:

...

This fixes a use after free bug, we need to do the del_gendisk after we cleanup the queue on the device.

Hello Josef,

Which use-after-free bug does this patch fix? Are you aware that most block drivers call blk_cleanup_queue() before calling del_gendisk()? Why do you think that the nbd driver should use the opposite order?

I'm confused, that's what this patch does. Before I had del_gendisk() first and then the blk_cleanup_queue(), which was bugging out when I was testing stuff with a null pointer deref whenever I rmmod'ed the nbd. Swapping it to the way everybody else did it fixed the problem. Thanks,

Josef