ida_alloc_range(..., min, max, ...) returns values from min to max,
inclusive.

So, '1 << (MINORBITS - RNBD_PART_BITS)' is a valid value for ret, which is
then saved in 'dev->clt_device_id'.

This value is used in rnbd_client_setup_device() and passed to
rnbd_clt_setup_gen_disk().
There we have:
    dev->gd->first_minor	= idx << RNBD_PART_BITS

So a possible value for 'gd->first_minor' is '1 << MINORBITS'

This is an issue because:
    rnbd_clt_setup_gen_disk()
    --> add_disk(dev->gd)
      --> device_add_disk(NULL, disk, NULL)

And there we have:
   ddev->devt = MKDEV(disk->major, disk->first_minor);

So, should 'gd->first_minor' be '1 << MINORBITS', MKDEV() would overflow.

Fixes: f7a7a5c228d4 ("block/rnbd: client: main functionality")
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
---
#define MKDEV(ma,mi)	(((ma) << MINORBITS) | (mi))

This patch is completely speculative.

I think that:
	if (disk->first_minor + disk->minors > MINORMASK + 1)
		return -EINVAL;
in device_add_disk() handles this corner case.
Anyway, if I'm correct, handling the error earlier can't hurt (at least I
guess so :)).

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
---
 drivers/block/rnbd/rnbd-clt.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/block/rnbd/rnbd-clt.c b/drivers/block/rnbd/rnbd-clt.c
index b66e8840b94b..db900c3786a3 100644
--- a/drivers/block/rnbd/rnbd-clt.c
+++ b/drivers/block/rnbd/rnbd-clt.c
@@ -1454,7 +1454,7 @@ static struct rnbd_clt_dev *init_dev(struct rnbd_clt_session *sess,
 		goto out_alloc;
 	}
 
-	ret = ida_alloc_max(&index_ida, 1 << (MINORBITS - RNBD_PART_BITS),
+	ret = ida_alloc_max(&index_ida, (1 << (MINORBITS - RNBD_PART_BITS)) - 1,
 			    GFP_KERNEL);
 	if (ret < 0) {
 		pr_err("Failed to initialize device '%s' from session %s, allocating idr failed, err: %d\n",
-- 
2.32.0

On Sun, Mar 27, 2022 at 1:06 PM Christophe JAILLET
<christophe.jaillet@wanadoo.fr> wrote:
>
> ida_alloc_range(..., min, max, ...) returns values from min to max,
> inclusive.
>
> So, '1 << (MINORBITS - RNBD_PART_BITS)' is a valid value for ret, which is
> then saved in 'dev->clt_device_id'.
>
> This value is used in rnbd_client_setup_device() and passed to
> rnbd_clt_setup_gen_disk().
> There we have:
>     dev->gd->first_minor        = idx << RNBD_PART_BITS
>
> So a possible value for 'gd->first_minor' is '1 << MINORBITS'
>
> This is an issue because:
>     rnbd_clt_setup_gen_disk()
>     --> add_disk(dev->gd)
>       --> device_add_disk(NULL, disk, NULL)
>
> And there we have:
>    ddev->devt = MKDEV(disk->major, disk->first_minor);
>
> So, should 'gd->first_minor' be '1 << MINORBITS', MKDEV() would overflow.
>
> Fixes: f7a7a5c228d4 ("block/rnbd: client: main functionality")
> Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
> ---
> #define MKDEV(ma,mi)    (((ma) << MINORBITS) | (mi))
>
> This patch is completely speculative.
>
> I think that:
>         if (disk->first_minor + disk->minors > MINORMASK + 1)
>                 return -EINVAL;
> in device_add_disk() handles this corner case.
> Anyway, if I'm correct, handling the error earlier can't hurt (at least I
> guess so :)).
>
> Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
looks good to me, thx!
Acked-by: Jack Wang <jinpu.wang@ionos.com>
> ---
>  drivers/block/rnbd/rnbd-clt.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/block/rnbd/rnbd-clt.c b/drivers/block/rnbd/rnbd-clt.c
> index b66e8840b94b..db900c3786a3 100644
> --- a/drivers/block/rnbd/rnbd-clt.c
> +++ b/drivers/block/rnbd/rnbd-clt.c
> @@ -1454,7 +1454,7 @@ static struct rnbd_clt_dev *init_dev(struct rnbd_clt_session *sess,
>                 goto out_alloc;
>         }
>
> -       ret = ida_alloc_max(&index_ida, 1 << (MINORBITS - RNBD_PART_BITS),
> +       ret = ida_alloc_max(&index_ida, (1 << (MINORBITS - RNBD_PART_BITS)) - 1,
>                             GFP_KERNEL);
>         if (ret < 0) {
>                 pr_err("Failed to initialize device '%s' from session %s, allocating idr failed, err: %d\n",
> --
> 2.32.0
>