From: Demi Marie Obenour <demi@invisiblethingslab.com>
To: "Jens Axboe" <axboe@kernel.dk>,
"Roger Pau Monné" <roger.pau@citrix.com>,
"Alasdair Kergon" <agk@redhat.com>,
"Mike Snitzer" <snitzer@kernel.org>,
dm-devel@redhat.com
Cc: "Demi Marie Obenour" <demi@invisiblethingslab.com>,
"Marek Marczykowski-Górecki" <marmarek@invisiblethingslab.com>,
linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
xen-devel@lists.xenproject.org
Subject: [PATCH v2 13/16] xen-blkback: Implement diskseq checks
Date: Tue, 30 May 2023 16:31:13 -0400 [thread overview]
Message-ID: <20230530203116.2008-14-demi@invisiblethingslab.com> (raw)
In-Reply-To: <20230530203116.2008-1-demi@invisiblethingslab.com>
This allows specifying a disk sequence number in XenStore. If it does
not match the disk sequence number of the underlying device, the device
will not be exported and a warning will be logged. Userspace can use
this to eliminate race conditions due to major/minor number reuse.
Old kernels do not support the new syntax, but a later patch will allow
userspace to discover that the new syntax is supported.
Signed-off-by: Demi Marie Obenour <demi@invisiblethingslab.com>
---
drivers/block/xen-blkback/xenbus.c | 112 +++++++++++++++++++++++------
1 file changed, 89 insertions(+), 23 deletions(-)
diff --git a/drivers/block/xen-blkback/xenbus.c b/drivers/block/xen-blkback/xenbus.c
index 4807af1d58059394d7a992335dabaf2bc3901721..9c3eb148fbd802c74e626c3d7bcd69dcb09bd921 100644
--- a/drivers/block/xen-blkback/xenbus.c
+++ b/drivers/block/xen-blkback/xenbus.c
@@ -24,6 +24,7 @@ struct backend_info {
struct xenbus_watch backend_watch;
unsigned major;
unsigned minor;
+ unsigned long long diskseq;
char *mode;
};
@@ -479,7 +480,7 @@ static void xen_vbd_free(struct xen_vbd *vbd)
static int xen_vbd_create(struct xen_blkif *blkif, blkif_vdev_t handle,
unsigned major, unsigned minor, int readonly,
- int cdrom)
+ bool cdrom, u64 diskseq)
{
struct xen_vbd *vbd;
struct block_device *bdev;
@@ -507,6 +508,26 @@ static int xen_vbd_create(struct xen_blkif *blkif, blkif_vdev_t handle,
xen_vbd_free(vbd);
return -ENOENT;
}
+
+ 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;
+ }
+
+ if (unlikely(disk->diskseq != diskseq)) {
+ pr_warn("%s: device %08x has incorrect sequence "
+ "number 0x%llx (expected 0x%llx)\n",
+ __func__, vbd->pdevice, disk->diskseq, diskseq);
+ xen_vbd_free(vbd);
+ return -ENODEV;
+ }
+ }
+
vbd->size = vbd_sz(vbd);
if (cdrom || disk_to_cdi(vbd->bdev->bd_disk))
@@ -707,6 +728,9 @@ static void backend_changed(struct xenbus_watch *watch,
int cdrom = 0;
unsigned long handle;
char *device_type;
+ char *diskseq_str = NULL;
+ int diskseq_len;
+ unsigned long long diskseq;
pr_debug("%s %p %d\n", __func__, dev, dev->otherend_id);
@@ -725,10 +749,46 @@ static void backend_changed(struct xenbus_watch *watch,
return;
}
- if (be->major | be->minor) {
- if (be->major != major || be->minor != minor)
- pr_warn("changing physical device (from %x:%x to %x:%x) not supported.\n",
- be->major, be->minor, major, minor);
+ diskseq_str = xenbus_read(XBT_NIL, dev->nodename, "diskseq", &diskseq_len);
+ 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
+ * 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) {
+ 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;
+ }
+
+ if (be->major | be->minor | be->diskseq) {
+ if (be->major != major || be->minor != minor || be->diskseq != diskseq)
+ pr_warn("changing physical device (from %x:%x:%llx to %x:%x:%llx)"
+ " not supported.\n",
+ be->major, be->minor, be->diskseq, major, minor, diskseq);
return;
}
@@ -756,29 +816,35 @@ static void backend_changed(struct xenbus_watch *watch,
be->major = major;
be->minor = minor;
+ be->diskseq = diskseq;
err = xen_vbd_create(be->blkif, handle, major, minor,
- !strchr(be->mode, 'w'), cdrom);
-
- if (err)
- xenbus_dev_fatal(dev, err, "creating vbd structure");
- else {
- err = xenvbd_sysfs_addif(dev);
- if (err) {
- xen_vbd_free(&be->blkif->vbd);
- xenbus_dev_fatal(dev, err, "creating sysfs entries");
- }
- }
+ !strchr(be->mode, 'w'), cdrom, diskseq);
if (err) {
- kfree(be->mode);
- be->mode = NULL;
- be->major = 0;
- be->minor = 0;
- } else {
- /* We're potentially connected now */
- xen_update_blkif_status(be->blkif);
+ xenbus_dev_fatal(dev, err, "creating vbd structure");
+ goto fail;
}
+
+ err = xenvbd_sysfs_addif(dev);
+ if (err) {
+ xenbus_dev_fatal(dev, err, "creating sysfs entries");
+ goto free_vbd;
+ }
+
+ /* We're potentially connected now */
+ xen_update_blkif_status(be->blkif);
+ return;
+
+free_vbd:
+ xen_vbd_free(&be->blkif->vbd);
+fail:
+ kfree(diskseq_str);
+ kfree(be->mode);
+ be->mode = NULL;
+ be->major = 0;
+ be->minor = 0;
+ be->diskseq = 0;
}
/*
--
Sincerely,
Demi Marie Obenour (she/her/hers)
Invisible Things Lab
next prev parent reply other threads:[~2023-05-30 20:33 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-05-30 20:31 [PATCH v2 00/16] Diskseq support in loop, device-mapper, and blkback Demi Marie Obenour
2023-05-30 20:31 ` [PATCH v2 01/16] device-mapper: Check that target specs are sufficiently aligned Demi Marie Obenour
2023-05-30 20:31 ` [PATCH v2 02/16] device-mapper: Avoid pointer arithmetic overflow Demi Marie Obenour
2023-05-30 20:31 ` [PATCH v2 03/16] device-mapper: do not allow targets to overlap 'struct dm_ioctl' Demi Marie Obenour
2023-05-30 20:31 ` [PATCH v2 04/16] device-mapper: Better error message for too-short target spec Demi Marie Obenour
2023-05-30 20:31 ` [PATCH v2 05/16] device-mapper: Target parameters must not overlap next " Demi Marie Obenour
2023-05-30 20:31 ` [PATCH v2 06/16] device-mapper: Avoid double-fetch of version Demi Marie Obenour
2023-05-30 20:31 ` [PATCH v2 07/16] device-mapper: Allow userspace to opt-in to strict parameter checks Demi Marie Obenour
2023-05-30 20:31 ` [PATCH v2 08/16] device-mapper: Allow userspace to provide expected diskseq Demi Marie Obenour
2023-05-30 20:31 ` [PATCH v2 09/16] device-mapper: Allow userspace to suppress uevent generation Demi Marie Obenour
2023-05-30 20:31 ` [PATCH v2 10/16] device-mapper: Refuse to create device named "control" Demi Marie Obenour
2023-05-30 20:31 ` [PATCH v2 11/16] device-mapper: "." and ".." are not valid symlink names Demi Marie Obenour
2023-05-30 20:31 ` [PATCH v2 12/16] device-mapper: inform caller about already-existing device Demi Marie Obenour
2023-05-30 20:31 ` Demi Marie Obenour [this message]
2023-06-06 8:25 ` [PATCH v2 13/16] xen-blkback: Implement diskseq checks Roger Pau Monné
2023-06-06 17:01 ` Demi Marie Obenour
2023-06-07 8:20 ` Roger Pau Monné
2023-06-07 16:14 ` Demi Marie Obenour
2023-06-08 8:29 ` Roger Pau Monné
2023-06-08 15:33 ` Demi Marie Obenour
2023-06-09 15:13 ` Roger Pau Monné
2023-06-09 16:55 ` Demi Marie Obenour
2023-06-12 8:09 ` Roger Pau Monné
2023-06-21 1:14 ` Demi Marie Obenour
2023-06-21 10:07 ` Roger Pau Monné
2023-05-30 20:31 ` [PATCH v2 14/16] block, loop: Increment diskseq when releasing a loop device Demi Marie Obenour
2023-05-30 20:31 ` [PATCH v2 15/16] xen-blkback: Minor cleanups Demi Marie Obenour
2023-06-06 8:36 ` Roger Pau Monné
2023-05-30 20:31 ` [PATCH v2 16/16] xen-blkback: Inform userspace that device has been opened Demi Marie Obenour
2023-06-06 9:15 ` Roger Pau Monné
2023-06-06 17:31 ` Demi Marie Obenour
2023-06-07 8:44 ` Roger Pau Monné
2023-06-07 16:29 ` Demi Marie Obenour
2023-06-08 9:11 ` Roger Pau Monné
2023-06-08 15:23 ` Demi Marie Obenour
2023-06-08 10:08 ` Roger Pau Monné
2023-06-08 15:24 ` Demi Marie Obenour
2023-05-31 13:06 ` [dm-devel] [PATCH v2 00/16] Diskseq support in loop, device-mapper, and blkback Christoph Hellwig
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