Re: [PATCH 1/2] xen-blkback: Implement diskseq checks

[Demi Marie Obenour <demi@xxxxxxxxxxxxxxxxxxxxxx>]

On Wed, Jun 07, 2023 at 12:44:22AM -0700, Christoph Hellwig wrote:
> On Thu, Jun 01, 2023 at 05:48:22PM -0400, Demi Marie Obenour wrote:
> > +   if (diskseq) {
> > +           struct gendisk *disk = bdev->bd_disk;
> > +
> > +           if (unlikely(disk == NULL)) {
> > +                   pr_err("%s: device %08x has no gendisk\n",
> > +                          __func__, vbd->pdevice);
> > +                   xen_vbd_free(vbd);
> > +                   return -EFAULT;
> > +           }
> 
> bdev->bd_disk is never NULL.

Fixed in v3.

> > +   diskseq_str = xenbus_read(XBT_NIL, dev->nodename, "diskseq", 
> > &diskseq_len);
> 
> Please avoid the overly long line.

Fixed in v3.

> > +   if (IS_ERR(diskseq_str)) {
> > +           int err = PTR_ERR(diskseq_str);
> > +           diskseq_str = NULL;
> > +
> > +           /*
> > +            * If this does not exist, it means legacy userspace that does 
> > not
> 
> .. even more so in comments.

Fixed in v3.

> > +            * support diskseq.
> > +            */
> > +           if (unlikely(!XENBUS_EXIST_ERR(err))) {
> > +                   xenbus_dev_fatal(dev, err, "reading diskseq");
> > +                   return;
> > +           }
> > +           diskseq = 0;
> > +   } else if (diskseq_len <= 0) {
> > +           xenbus_dev_fatal(dev, -EFAULT, "diskseq must not be empty");
> > +           goto fail;
> > +   } else if (diskseq_len > 16) {
> 
> No need for a else after a return.

Fixed in v3.

> > +           xenbus_dev_fatal(dev, -ERANGE, "diskseq too long: got %d but 
> > limit is 16",
> > +                            diskseq_len);
> > +           goto fail;
> > +   } else if (diskseq_str[0] == '0') {
> > +           xenbus_dev_fatal(dev, -ERANGE, "diskseq must not start with 
> > '0'");
> > +           goto fail;
> > +   } else {
> > +           char *diskseq_end;
> > +           diskseq = simple_strtoull(diskseq_str, &diskseq_end, 16);
> > +           if (diskseq_end != diskseq_str + diskseq_len) {
> > +                   xenbus_dev_fatal(dev, -EINVAL, "invalid diskseq");
> > +                   goto fail;
> > +           }
> > +           kfree(diskseq_str);
> > +           diskseq_str = NULL;
> > +   }
> 
> And I suspect the code will be a lot easier to follow if you move
> the diskseq validation into a separate helper.

Fixed in v3.
-- 
Sincerely,
Demi Marie Obenour (she/her/hers)
Invisible Things Lab

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