{"api_version":"1","generated_at":"2026-08-13T09:07:40+00:00","cve":"CVE-2026-68173","urls":{"html":"https://cve.report/CVE-2026-68173","api":"https://cve.report/api/cve/CVE-2026-68173.json","docs":"https://cve.report/api","cve_org":"https://www.cve.org/CVERecord?id=CVE-2026-68173","nvd":"https://nvd.nist.gov/vuln/detail/CVE-2026-68173"},"summary":{"title":"ublk: wait on ublk_dev_ready() instead of ub->completion","description":"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.","state":"PUBLISHED","assigner":"Linux","published_at":"2026-08-10 13:20:04","updated_at":"2026-08-10 13:20:04"},"problem_types":[],"metrics":[],"references":[{"url":"https://git.kernel.org/stable/c/432a9b2780c0a01caf547bd1fc2fcf28aeb8d173","name":"https://git.kernel.org/stable/c/432a9b2780c0a01caf547bd1fc2fcf28aeb8d173","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/8f188dd11a1c2ad94caeaee36ef68bb8221d4a12","name":"https://git.kernel.org/stable/c/8f188dd11a1c2ad94caeaee36ef68bb8221d4a12","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/7dd26adf7e7d482af524e3a0cca4a81ef7c159d0","name":"https://git.kernel.org/stable/c/7dd26adf7e7d482af524e3a0cca4a81ef7c159d0","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://www.cve.org/CVERecord?id=CVE-2026-68173","name":"CVE Program record","refsource":"CVE.ORG","tags":["canonical"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-68173","name":"NVD vulnerability detail","refsource":"NVD","tags":["canonical","analysis"]}],"affected":[{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 728cbac5fe219d3b8a21a0688a08f2b7f8aeda2b 7dd26adf7e7d482af524e3a0cca4a81ef7c159d0 git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 728cbac5fe219d3b8a21a0688a08f2b7f8aeda2b 8f188dd11a1c2ad94caeaee36ef68bb8221d4a12 git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 728cbac5fe219d3b8a21a0688a08f2b7f8aeda2b 432a9b2780c0a01caf547bd1fc2fcf28aeb8d173 git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 42ea64e01c96e594fb4f80c54dfe4f934d008a6e git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 6.14.6 6.15 semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 6.15","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 6.15 semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 6.18.42 6.18.* semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 7.1.6 7.1.* semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 7.2-rc5 * original_commit_for_fix","platforms":[]}],"timeline":[],"solutions":[],"workarounds":[],"exploits":[],"credits":[],"nvd_cpes":[],"vendor_comments":[],"enrichments":{"kev":null,"epss":null,"legacy_qids":[]},"source_records":{"cve_program":{"containers":{"cna":{"affected":[{"defaultStatus":"unaffected","product":"Linux","programFiles":["drivers/block/ublk_drv.c"],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","vendor":"Linux","versions":[{"lessThan":"7dd26adf7e7d482af524e3a0cca4a81ef7c159d0","status":"affected","version":"728cbac5fe219d3b8a21a0688a08f2b7f8aeda2b","versionType":"git"},{"lessThan":"8f188dd11a1c2ad94caeaee36ef68bb8221d4a12","status":"affected","version":"728cbac5fe219d3b8a21a0688a08f2b7f8aeda2b","versionType":"git"},{"lessThan":"432a9b2780c0a01caf547bd1fc2fcf28aeb8d173","status":"affected","version":"728cbac5fe219d3b8a21a0688a08f2b7f8aeda2b","versionType":"git"},{"status":"affected","version":"42ea64e01c96e594fb4f80c54dfe4f934d008a6e","versionType":"git"},{"lessThan":"6.15","status":"affected","version":"6.14.6","versionType":"semver"}]},{"defaultStatus":"affected","product":"Linux","programFiles":["drivers/block/ublk_drv.c"],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","vendor":"Linux","versions":[{"status":"affected","version":"6.15"},{"lessThan":"6.15","status":"unaffected","version":"0","versionType":"semver"},{"lessThanOrEqual":"6.18.*","status":"unaffected","version":"6.18.42","versionType":"semver"},{"lessThanOrEqual":"7.1.*","status":"unaffected","version":"7.1.6","versionType":"semver"},{"lessThanOrEqual":"*","status":"unaffected","version":"7.2-rc5","versionType":"original_commit_for_fix"}]}],"cpeApplicability":[{"nodes":[{"cpeMatch":[{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"6.18.42","versionStartIncluding":"6.15","vulnerable":true},{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"7.1.6","versionStartIncluding":"6.15","vulnerable":true},{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"7.2-rc5","versionStartIncluding":"6.15","vulnerable":true},{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.14.6","vulnerable":true}],"negate":false,"operator":"OR"}]}],"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."}],"providerMetadata":{"dateUpdated":"2026-08-10T11:59:42.889Z","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","shortName":"Linux"},"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"}}},"cveMetadata":{"assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","assignerShortName":"Linux","cveId":"CVE-2026-68173","datePublished":"2026-08-10T11:59:42.889Z","dateReserved":"2026-07-30T09:28:09.372Z","dateUpdated":"2026-08-10T11:59:42.889Z","state":"PUBLISHED"},"dataType":"CVE_RECORD","dataVersion":"5.2"},"nvd":{"publishedDate":"2026-08-10 13:20:04","lastModifiedDate":"2026-08-10 13:20:04","problem_types":[],"metrics":[],"configurations":[]},"legacy_mitre":{"record":{"CveYear":"2026","CveId":"68173","Ordinal":"1","Title":"ublk: wait on ublk_dev_ready() instead of ub->completion","CVE":"CVE-2026-68173","Year":"2026"},"notes":[{"CveYear":"2026","CveId":"68173","Ordinal":"1","NoteData":"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.","Type":"Description","Title":"ublk: wait on ublk_dev_ready() instead of ub->completion"}]}}}