From: "Roger Pau Monné" <roger.pau@citrix.com>
To: Dongli Zhang <dongli.zhang@oracle.com>
Cc: <linux-kernel@vger.kernel.org>, <xen-devel@lists.xenproject.org>,
<linux-block@vger.kernel.org>, <konrad.wilk@oracle.com>,
<axboe@kernel.dk>
Subject: Re: [PATCH 1/1] xen/blkback: rework connect_ring() to avoid inconsistent xenstore 'ring-page-order' set by malicious blkfront
Date: Mon, 10 Dec 2018 16:14:47 +0100 [thread overview]
Message-ID: <20181210151447.jezcmwn6lzyq5xzd@mac> (raw)
In-Reply-To: <1544156284-7756-1-git-send-email-dongli.zhang@oracle.com>
On Fri, Dec 07, 2018 at 12:18:04PM +0800, Dongli Zhang wrote:
> The xenstore 'ring-page-order' is used globally for each blkback queue and
> therefore should be read from xenstore only once. However, it is obtained
> in read_per_ring_refs() which might be called multiple times during the
> initialization of each blkback queue.
>
> If the blkfront is malicious and the 'ring-page-order' is set in different
> value by blkfront every time before blkback reads it, this may end up at
> the "WARN_ON(i != (XEN_BLKIF_REQS_PER_PAGE * blkif->nr_ring_pages));" in
> xen_blkif_disconnect() when frontend is destroyed.
>
> This patch reworks connect_ring() to read xenstore 'ring-page-order' only
> once.
>
> Signed-off-by: Dongli Zhang <dongli.zhang@oracle.com>
> ---
> drivers/block/xen-blkback/xenbus.c | 49 ++++++++++++++++++++++++--------------
> 1 file changed, 31 insertions(+), 18 deletions(-)
>
> diff --git a/drivers/block/xen-blkback/xenbus.c b/drivers/block/xen-blkback/xenbus.c
> index a4bc74e..4a8ce20 100644
> --- a/drivers/block/xen-blkback/xenbus.c
> +++ b/drivers/block/xen-blkback/xenbus.c
> @@ -919,14 +919,15 @@ static void connect(struct backend_info *be)
> /*
> * Each ring may have multi pages, depends on "ring-page-order".
> */
> -static int read_per_ring_refs(struct xen_blkif_ring *ring, const char *dir)
> +static int read_per_ring_refs(struct xen_blkif_ring *ring, const char *dir,
> + bool use_ring_page_order)
Why not change the order of read_per_ring_refs so that it tries to
fetch the grant references from "ring-refXX" first and then fallback
to reading the legacy grant reference if nr_ring_pages == 1?
This will avoid having to pass an extra parameter to it.
> {
> unsigned int ring_ref[XENBUS_MAX_RING_GRANTS];
> struct pending_req *req, *n;
> int err, i, j;
> struct xen_blkif *blkif = ring->blkif;
> struct xenbus_device *dev = blkif->be->dev;
> - unsigned int ring_page_order, nr_grefs, evtchn;
> + unsigned int nr_grefs, evtchn;
>
> err = xenbus_scanf(XBT_NIL, dir, "event-channel", "%u",
> &evtchn);
> @@ -936,28 +937,18 @@ static int read_per_ring_refs(struct xen_blkif_ring *ring, const char *dir)
> return err;
> }
>
> - err = xenbus_scanf(XBT_NIL, dev->otherend, "ring-page-order", "%u",
> - &ring_page_order);
> - if (err != 1) {
> + nr_grefs = blkif->nr_ring_pages;
> +
> + if (!use_ring_page_order) {
> err = xenbus_scanf(XBT_NIL, dir, "ring-ref", "%u", &ring_ref[0]);
> if (err != 1) {
> err = -EINVAL;
> xenbus_dev_fatal(dev, err, "reading %s/ring-ref", dir);
> return err;
> }
> - nr_grefs = 1;
> } else {
> unsigned int i;
>
> - if (ring_page_order > xen_blkif_max_ring_order) {
> - err = -EINVAL;
> - xenbus_dev_fatal(dev, err, "%s/request %d ring page order exceed max:%d",
> - dir, ring_page_order,
> - xen_blkif_max_ring_order);
> - return err;
> - }
> -
> - nr_grefs = 1 << ring_page_order;
> for (i = 0; i < nr_grefs; i++) {
> char ring_ref_name[RINGREF_NAME_LEN];
>
> @@ -972,7 +963,6 @@ static int read_per_ring_refs(struct xen_blkif_ring *ring, const char *dir)
> }
> }
> }
> - blkif->nr_ring_pages = nr_grefs;
>
> for (i = 0; i < nr_grefs * XEN_BLKIF_REQS_PER_PAGE; i++) {
> req = kzalloc(sizeof(*req), GFP_KERNEL);
> @@ -1030,6 +1020,8 @@ static int connect_ring(struct backend_info *be)
> size_t xspathsize;
> const size_t xenstore_path_ext_size = 11; /* sufficient for "/queue-NNN" */
> unsigned int requested_num_queues = 0;
> + bool use_ring_page_order = false;
> + unsigned int ring_page_order;
>
> pr_debug("%s %s\n", __func__, dev->otherend);
>
> @@ -1075,8 +1067,28 @@ static int connect_ring(struct backend_info *be)
> be->blkif->nr_rings, be->blkif->blk_protocol, protocol,
> pers_grants ? "persistent grants" : "");
>
> + err = xenbus_scanf(XBT_NIL, dev->otherend, "ring-page-order", "%u",
> + &ring_page_order);
You can use xenbus_read_unsigned IMO, which will simplify the logic
below a little bit.
Thanks, Roger.
prev parent reply other threads:[~2018-12-10 15:15 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-12-07 4:18 [PATCH 1/1] xen/blkback: rework connect_ring() to avoid inconsistent xenstore 'ring-page-order' set by malicious blkfront Dongli Zhang
2018-12-07 9:39 ` [Xen-devel] " Paul Durrant
2018-12-07 15:10 ` Dongli Zhang
2018-12-07 15:15 ` Paul Durrant
2018-12-07 15:50 ` Dongli Zhang
2018-12-10 15:14 ` Roger Pau Monné [this message]
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20181210151447.jezcmwn6lzyq5xzd@mac \
--to=roger.pau@citrix.com \
--cc=axboe@kernel.dk \
--cc=dongli.zhang@oracle.com \
--cc=konrad.wilk@oracle.com \
--cc=linux-block@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=xen-devel@lists.xenproject.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).