{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-68173","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","state":"PUBLISHED","assignerShortName":"Linux","dateReserved":"2026-07-30T09:28:09.372Z","datePublished":"2026-08-10T11:59:42.889Z","dateUpdated":"2026-08-17T05:00:14.047Z"},"containers":{"cna":{"providerMetadata":{"orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","shortName":"Linux","dateUpdated":"2026-08-17T05:00:14.047Z"},"descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\nublk: wait on ublk_dev_ready() instead of ub->completion\n\nub->completion is only re-armed by a successful START_USER_RECOVERY. If\nthe ublk server sends END_USER_RECOVERY without one - e.g. its START\nfailed with -EBUSY and the error was ignored - the wait is satisfied by\nthe stale completion of the previous recovery cycle, and the device is\nmarked LIVE and the requeue list kicked while the FETCH stream is still\nrunning and ubq->canceling is still set. The kick redispatches a\npreviously requeued request, __ublk_queue_rq_common() sees ->canceling\nand parks it again via __ublk_abort_rq(), and after the last FETCH\nclears ->canceling nothing ever kicks the requeue list again: the\nrequest is stranded there while holding its tag. If it is the flush\nmachinery's flush_rq, every subsequent fsync piles up in uninterruptible\nsleep and teardown hangs on tag draining. This matches a report of a\nlost PREFLUSH with ext4 on top of ublk after daemon crash recovery.\n\nub->completion is an edge-triggered latch used as a proxy for the level\ncondition \"every queue has fetched all I/O commands\", which can regress\n(F_BATCH's UNPREP, daemon death) and whose re-arm can be skipped. Drop\nit and wait on the real condition instead: the new helper\nublk_wait_dev_ready_and_lock() waits on ublk_dev_ready() via\nwait_var_event_interruptible(), woken from ublk_mark_io_ready(), then\nre-checks it under ub->mutex, waiting again on regression, and returns\nwith the mutex held and readiness guaranteed.\n\nReadiness becomes true in the same ub->mutex critical section that\nclears the last queue's ->canceling, so END_USER_RECOVERY marks the\ndevice LIVE and kicks the requeue list strictly after ->canceling\nclears. The wait stays interruptible, so a server whose daemon died can\nstill be signalled out. For ublk_ctrl_start_dev() this replaces the\nfail-fast -EINVAL on an F_BATCH ready->UNPREP regression with waiting\nuntil the device is ready again."}],"metrics":[{"cvssV3_1":{"version":"3.1","vectorString":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:H","baseScore":7.1,"baseSeverity":"HIGH"},"scenarios":[{"lang":"en","value":"AV:L - The bug is reached only via io_uring commands (UBLK_CMD_END_USER_RECOVERY/UBLK_CMD_START_DEV) on /dev/ublk-control or ublk char devices; there is no network, Bluetooth, or physical-bus entry path to the vulnerable wait/completion logic.\nAC:L - An actor controlling the ublk server can reliably trigger stale-completion early wakeup by calling END_USER_RECOVERY after START_USER_RECOVERY failed (e.g., -EBUSY) without re-arming completion; the attacker controls both sides of the recovery sequence and needs no uncontrollable timing.\nPR:L - Recovery requires UBLK_F_USER_RECOVERY devices managed through ublk-control, which needs CAP_SYS_ADMIN for privileged devices; per kernel CNA guidance, CAP_SYS_ADMIN obtainable in a user namespace (unshare -Urn) counts as Low, not High.\nUI:N - Exploitation is driven by the ublk daemon issuing recovery/start control commands during crash recovery or restart; no end-user action such as opening files, mounting media, or clicking prompts is required.\nS:U - Impact is confined to the kernel block/ublk stack and filesystems backed by the affected ublk device; it does not cross VM, container, or IOMMU boundaries into a separate security authority.\nC:N - This is a state-machine/completion synchronization flaw, not memory corruption; it strands block requests and breaks flush barriers but does not read or disclose kernel or user memory.\nI:H - Premature END_USER_RECOVERY can strand the block layer flush_rq and lose PREFLUSH ordering (reported with ext4), breaking durability guarantees and allowing arbitrary user data loss or corruption after crash or power loss.\nA:H - Stranded flush_rq holds its MQ tag indefinitely, causing every subsequent fsync to sleep uninterruptibly (D state) and device teardown to hang on tag draining, producing a persistent kernel-level denial of service on the backing block device."}]}],"affected":[{"product":"Linux","vendor":"Linux","defaultStatus":"unaffected","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["drivers/block/ublk_drv.c"],"versions":[{"version":"728cbac5fe219d3b8a21a0688a08f2b7f8aeda2b","lessThan":"7dd26adf7e7d482af524e3a0cca4a81ef7c159d0","status":"affected","versionType":"git"},{"version":"728cbac5fe219d3b8a21a0688a08f2b7f8aeda2b","lessThan":"8f188dd11a1c2ad94caeaee36ef68bb8221d4a12","status":"affected","versionType":"git"},{"version":"728cbac5fe219d3b8a21a0688a08f2b7f8aeda2b","lessThan":"432a9b2780c0a01caf547bd1fc2fcf28aeb8d173","status":"affected","versionType":"git"},{"version":"42ea64e01c96e594fb4f80c54dfe4f934d008a6e","status":"affected","versionType":"git"},{"version":"6.14.6","lessThan":"6.15","status":"affected","versionType":"semver"}]},{"product":"Linux","vendor":"Linux","defaultStatus":"affected","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["drivers/block/ublk_drv.c"],"versions":[{"version":"6.15","status":"affected"},{"version":"0","lessThan":"6.15","status":"unaffected","versionType":"semver"},{"version":"6.18.42","lessThanOrEqual":"6.18.*","status":"unaffected","versionType":"semver"},{"version":"7.1.6","lessThanOrEqual":"7.1.*","status":"unaffected","versionType":"semver"},{"version":"7.2","lessThanOrEqual":"*","status":"unaffected","versionType":"original_commit_for_fix"}]}],"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.15","versionEndExcluding":"6.18.42"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.15","versionEndExcluding":"7.1.6"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.15","versionEndExcluding":"7.2"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.14.6"}]}]}],"references":[{"url":"https://git.kernel.org/stable/c/7dd26adf7e7d482af524e3a0cca4a81ef7c159d0"},{"url":"https://git.kernel.org/stable/c/8f188dd11a1c2ad94caeaee36ef68bb8221d4a12"},{"url":"https://git.kernel.org/stable/c/432a9b2780c0a01caf547bd1fc2fcf28aeb8d173"}],"title":"ublk: wait on ublk_dev_ready() instead of ub->completion","x_generator":{"engine":"bippy-1.2.0"}}}}