Re: [PATCH] nvme: prevent double free in nvme_alloc_ns() error handling

[Niklas Cassel]

On Mon, Apr 27, 2020 at 08:03:11PM +0200, Javier González wrote:
> On 27.04.2020 14:34, Niklas Cassel wrote:
> > When jumping to the out_put_disk label, we will call put_disk(), which will
> > trigger a call to disk_release(), which calls blk_put_queue().
> > 
> > Later in the cleanup code, we do blk_cleanup_queue(), which will also call
> > blk_put_queue().
> > 
> > Putting the queue twice is incorrect, and will generate a KASAN splat.
> > 
> > Set the disk->queue pointer to NULL, before calling put_disk(), so that the
> > first call to blk_put_queue() will not free the queue.
> > 
> > The second call to blk_put_queue() uses another pointer to the same queue,
> > so this call will still free the queue.
> > 
> > Fixes: 85136c010285 ("lightnvm: simplify geometry enumeration")
> > Signed-off-by: Niklas Cassel <niklas.cassel@xxxxxxx>
> > ---
> > drivers/nvme/host/core.c | 2 ++
> > 1 file changed, 2 insertions(+)
> > 
> > diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
> > index 91c1bd659947..f2adea96b04c 100644
> > --- a/drivers/nvme/host/core.c
> > +++ b/drivers/nvme/host/core.c
> > @@ -3642,6 +3642,8 @@ static void nvme_alloc_ns(struct nvme_ctrl *ctrl, unsigned nsid)
> > 
> >       return;
> >  out_put_disk:
> > +      /* prevent double queue cleanup */
> > +      ns->disk->queue = NULL;
> >       put_disk(ns->disk);
> >  out_unlink_ns:
> >       mutex_lock(&ctrl->subsys->lock);
> > --
> > 2.25.3
> > 
> What about delaying the assignment of ns->disk?
> 
> diff --git i/drivers/nvme/host/core.c w/drivers/nvme/host/core.c
> index a4d8c90ee7cc..6da4a9ced945 100644
> --- i/drivers/nvme/host/core.c
> +++ w/drivers/nvme/host/core.c
> @@ -3541,7 +3541,6 @@ static int nvme_alloc_ns(struct nvme_ctrl *ctrl, unsigned nsid)
>         disk->queue = ns->queue;
>         disk->flags = flags;
>         memcpy(disk->disk_name, disk_name, DISK_NAME_LEN);
> -       ns->disk = disk;
> 
>         __nvme_revalidate_disk(disk, id);
> 
> @@ -3553,6 +3552,8 @@ static int nvme_alloc_ns(struct nvme_ctrl *ctrl, unsigned nsid)
>                 }
>         }
> 
> +       ns->disk = disk;
> +

Hello Javier!


The only case where we jump to the out_put_disk label, is if the
nvme_nvm_register() call failed.

In that case, we want to undo the alloc_disk_node() operation, i.e.,
decrease the refcount.

If we don't set "ns->disk = disk;" before the call to nvme_nvm_register(),
then, if register fails, and we jump to the put_disk(ns->disk) label,
ns->disk will be NULL, so the recount will not be decreased, so I assume
that this memory would then be a memory leak.


I think that the problem is that the block functions are a bit messy.
Most drivers seem to do blk_cleanup_queue() first and then do put_disk(),
but some drivers do it in the opposite way, so I think that we might have
some more use-after-free bugs in some of these drivers that do it in the
opposite way.


Kind regards,
Niklas

>         down_write(&ctrl->namespaces_rwsem);
>         list_add_tail(&ns->list, &ctrl->namespaces);
>         up_write(&ctrl->namespaces_rwsem);
> 
> 
> Javier