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bh=sHxeYo7zgfjFc cvxCuuph95svfpElxK2vn8+J41Up4A=; b=XIQCpZ3lX4/2fvGEl+smR04IQxUTp YuK64iAV32C+MVzzlelSu8NtBFy3/erKTDaWxxRgFI9OYqQVuQ/DJz9Tv+hoFKOm 4FxRc/bDupPlBYUU4UYdCHegdxMEunUBGzNtYiKm9AtHfexmQpZVGpBIxAahaA1T fvGb/rfnrO7ezrUMGViTPOF1DjPNXbqTAxFzq3hW9JBb0TLR8dNXWzO1JOmt26Eb tvOejPXmncG8791tijP4bM4Kd9ujFo1RIPbMn81uxM3JiB5xsMiPNiHHrpZi1QYx Yea9SHaJ1U7hOEBIAMxH2y4mx1MZa2AwwK0EUaeLP30w2vkPrVQp9AZWw== X-ME-Sender: X-ME-Received: X-ME-Proxy-Cause: gggruggvucftvghtrhhoucdtuddrgedvhedruddvfedgheelucetufdoteggodetrfdotf fvucfrrhhofhhilhgvmecuhfgrshhtofgrihhlpdfqfgfvpdfurfetoffkrfgpnffqhgen uceurghilhhouhhtmecufedttdenucesvcftvggtihhpihgvnhhtshculddquddttddmne cujfgurhephffvvefufffkofgjfhgggfestdekredtredttdenucfhrhhomhepffgvmhhi ucforghrihgvucfqsggvnhhouhhruceouggvmhhisehinhhvihhsihgslhgvthhhihhngh hslhgrsgdrtghomheqnecuggftrfgrthhtvghrnhepjeffjefggfeugeduvedvjeekgfeh gffhhfffjeetkeelueefffetfffhtdduheetnecuvehluhhsthgvrhfuihiivgeptdenuc frrghrrghmpehmrghilhhfrhhomhepuggvmhhisehinhhvihhsihgslhgvthhhihhnghhs lhgrsgdrtghomh X-ME-Proxy: Feedback-ID: iac594737:Fastmail From: Demi Marie Obenour To: =?utf-8?q?Roger_Pau_Monn=C3=A9?= , Juergen Gross , Jens Axboe Cc: Demi Marie Obenour , =?utf-8?q?Marek_Marczykowski?= =?utf-8?q?-G=C3=B3recki?= , xen-devel@lists.xenproject.org, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, Demi Marie Obenour Subject: [RFC PATCH 3/7] Implement diskseq checks in blkback Date: Wed, 25 Jan 2023 22:33:55 -0500 Message-Id: <20230126033358.1880-4-demi@invisiblethingslab.com> X-Mailer: git-send-email 2.39.1 In-Reply-To: <20230126033358.1880-1-demi@invisiblethingslab.com> References: <20230126033358.1880-1-demi@invisiblethingslab.com> MIME-Version: 1.0 From: Demi Marie Obenour 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. Older kernels will ignore this, so it is safe for userspace to set it unconditionally. This also makes physical-device parsing stricter. I do not believe this will break any extant userspace tools. Signed-off-by: Demi Marie Obenour --- drivers/block/xen-blkback/xenbus.c | 137 +++++++++++++++++++++-------- 1 file changed, 100 insertions(+), 37 deletions(-) diff --git a/drivers/block/xen-blkback/xenbus.c b/drivers/block/xen-blkback/xenbus.c index 4807af1d58059394d7a992335dabaf2bc3901721..2c43bfc7ab5ba6954f11d4b949a5668660dbd290 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 +508,25 @@ 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("xen_vbd_create: device %08x has no gendisk\n", + vbd->pdevice); + xen_vbd_free(vbd); + return -EFAULT; + } + + if (unlikely(disk->diskseq != diskseq)) { + pr_warn("xen_vbd_create: device %08x has incorrect sequence " + "number 0x%llx (expected 0x%llx)\n", + 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)) @@ -690,6 +710,55 @@ static int xen_blkbk_probe(struct xenbus_device *dev, return err; } +static bool read_physical_device(struct xenbus_device *dev, + unsigned long long *diskseq, + unsigned *major, unsigned *minor) +{ + char *physical_device, *problem; + int i, physical_device_length; + char junk; + + physical_device = xenbus_read(XBT_NIL, dev->nodename, "physical-device", + &physical_device_length); + + if (IS_ERR(physical_device)) { + int err = PTR_ERR(physical_device); + /* + * Since this watch will fire once immediately after it is + * registered, we expect "does not exist" errors. Ignore + * them and wait for the hotplug scripts. + */ + if (unlikely(!XENBUS_EXIST_ERR(err))) + xenbus_dev_fatal(dev, err, "reading physical-device"); + return false; + } + + for (i = 0; i < physical_device_length; ++i) + if (unlikely(physical_device[i] <= 0x20 || physical_device[i] >= 0x7F)) { + problem = "bad byte in physical-device"; + goto fail; + } + + if (sscanf(physical_device, "%16llx@%8x:%8x%c", + diskseq, major, minor, &junk) == 3) { + if (*diskseq == 0) { + problem = "diskseq 0 is invalid"; + goto fail; + } + } else if (sscanf(physical_device, "%8x:%8x%c", major, minor, &junk) == 2) { + *diskseq = 0; + } else { + problem = "invalid physical-device"; + goto fail; + } + kfree(physical_device); + return true; +fail: + kfree(physical_device); + xenbus_dev_fatal(dev, -EINVAL, problem); + return false; +} + /* * Callback received when the hotplug scripts have placed the physical-device * node. Read it and the mode node, and create a vbd. If the frontend is @@ -707,28 +776,17 @@ static void backend_changed(struct xenbus_watch *watch, int cdrom = 0; unsigned long handle; char *device_type; + unsigned long long diskseq; pr_debug("%s %p %d\n", __func__, dev, dev->otherend_id); - - err = xenbus_scanf(XBT_NIL, dev->nodename, "physical-device", "%x:%x", - &major, &minor); - if (XENBUS_EXIST_ERR(err)) { - /* - * Since this watch will fire once immediately after it is - * registered, we expect this. Ignore it, and wait for the - * hotplug scripts. - */ + if (!read_physical_device(dev, &diskseq, &major, &minor)) return; - } - if (err != 2) { - xenbus_dev_fatal(dev, err, "reading physical-device"); - 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); + 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 +814,34 @@ 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(be->mode); + be->mode = NULL; + be->major = 0; + be->minor = 0; + be->diskseq = 0; } /*