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

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Message-ID: <ZICpodHAGv8qRw5A@itl-email>
Date:   Wed, 7 Jun 2023 12:00:29 -0400
From:   Demi Marie Obenour <demi@...isiblethingslab.com>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     Roger Pau Monné <roger.pau@...rix.com>,
        Jens Axboe <axboe@...nel.dk>,
        Marek Marczykowski-Górecki 
        <marmarek@...isiblethingslab.com>, xen-devel@...ts.xenproject.org,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] xen-blkback: Implement diskseq checks

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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