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Tue, 30 May 2023 16:32:11 -0400 (EDT) From: Demi Marie Obenour To: Jens Axboe , =?utf-8?q?Roger_Pau_Monn=C3=A9?= , Alasdair Kergon , Mike Snitzer , dm-devel@redhat.com Date: Tue, 30 May 2023 16:31:13 -0400 Message-Id: <20230530203116.2008-14-demi@invisiblethingslab.com> In-Reply-To: <20230530203116.2008-1-demi@invisiblethingslab.com> References: <20230530203116.2008-1-demi@invisiblethingslab.com> MIME-Version: 1.0 X-Mimecast-Impersonation-Protect: Policy=CLT - Impersonation Protection Definition; Similar Internal Domain=false; Similar Monitored External Domain=false; Custom External Domain=false; Mimecast External Domain=false; Newly Observed Domain=false; Internal User Name=false; Custom Display Name List=false; Reply-to Address Mismatch=false; Targeted Threat Dictionary=false; Mimecast Threat Dictionary=false; Custom Threat Dictionary=false X-Scanned-By: MIMEDefang 3.1 on 10.11.54.3 X-Mailman-Approved-At: Tue, 30 May 2023 20:54:23 +0000 Subject: [dm-devel] [PATCH v2 13/16] xen-blkback: Implement diskseq checks X-BeenThere: dm-devel@redhat.com X-Mailman-Version: 2.1.29 Precedence: list List-Id: device-mapper development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Demi Marie Obenour , linux-block@vger.kernel.org, xen-devel@lists.xenproject.org, =?utf-8?q?Mare?= =?utf-8?q?k_Marczykowski-G=C3=B3recki?= , linux-kernel@vger.kernel.org Errors-To: dm-devel-bounces@redhat.com Sender: "dm-devel" X-Scanned-By: MIMEDefang 3.1 on 10.11.54.5 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: 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 --- 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; } /*