{"id":"CVE-2026-68132","url":"https://www.cyber-defence.io/tools/cve/CVE-2026-68132","generatedAt":"2026-10-28T04:46:31.726Z","title":"In the Linux kernel, the following vulnerability has been resolved: super: fix emergency thaw deadlock on frozen block devices do_thaw_all_callback() calls bdev_thaw() while holding sb->s_umount exclusively.","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nsuper: fix emergency thaw deadlock on frozen block devices\n\ndo_thaw_all_callback() calls bdev_thaw() while holding sb->s_umount\nexclusively. If the block device was frozen via bdev_freeze() dropping\nthe last block layer freeze reference calls fs_bdev_thaw() which\nreacquires s_umount:\n\n  do_thaw_all_callback(sb)\n    super_lock_excl(sb)                     # holds sb->s_umount\n    bdev_thaw(sb->s_bdev)\n      mutex_lock(&bdev->bd_fsfreeze_mutex)\n      # bd_fsfreeze_count drops 1 -> 0\n      bd_holder_ops->thaw == fs_bdev_thaw\n        get_bdev_super(bdev)\n          bdev_super_lock(bdev, true)\n            super_lock(sb, true)\n              down_write(&sb->s_umount)     # same task: deadlock\n\nThe emergency thaw worker deadlocks against itself holding both\ns_umount and bd_fsfreeze_mutex. That fscks any subsequent unmount,\nfreeze, or thaw of that filesystem and block device.\n\n  [   81.878470] sysrq: Show Blocked State\n  [   81.880140] task:kworker/0:1     state:D stack:0     pid:11    tgid:11    ppid:2      task_flags:0x4208060 flags:0x00080000\n  [   81.884876] Workqueue: events do_thaw_all\n  [   81.886656] Call Trace:\n  [   81.887759]  <TASK>\n  [   81.888763]  __schedule+0x579/0x1420\n  [   81.890372]  schedule+0x3a/0x100\n  [   81.891794]  schedule_preempt_disabled+0x15/0x30\n  [   81.893848]  rwsem_down_write_slowpath+0x1ea/0x900\n  [   81.895191]  ? __pfx_do_thaw_all_callback+0x10/0x10\n  [   81.896528]  down_write+0xbd/0xc0\n  [   81.897505]  super_lock+0x91/0x180\n  [   81.898457]  ? __mutex_lock+0xa99/0x1140\n  [   81.900748]  ? __mutex_unlock_slowpath+0x1f/0x400\n  [   81.902069]  bdev_super_lock+0x5b/0x150\n  [   81.903132]  get_bdev_super+0x10/0x60\n  [   81.904042]  fs_bdev_thaw+0x23/0xf0\n  [   81.904755]  bdev_thaw+0x82/0x100\n  [   81.905484]  do_thaw_all_callback+0x2c/0x50\n  [   81.906298]  __iterate_supers+0x5d/0x130\n  [   81.907067]  do_thaw_all+0x20/0x40\n  [   81.907739]  process_one_work+0x206/0x5e0\n  [   81.908545]  worker_thread+0x1e2/0x3c0\n  [   81.909339]  ? __pfx_worker_thread+0x10/0x10\n  [   81.910171]  kthread+0xf4/0x130\n  [   81.910799]  ? __pfx_kthread+0x10/0x10\n  [   81.911528]  ret_from_fork+0x2e2/0x3b0\n  [   81.912259]  ? __pfx_kthread+0x10/0x10\n  [   81.913010]  ret_from_fork_asm+0x1a/0x30\n  [   81.913806]  </TASK>\n\nbdev_super_lock() even documents the violated requirement with\nlockdep_assert_not_held(&sb->s_umount).\n\nAcquiring bd_fsfreeze_mutex under s_umount also inverts the\nbd_fsfreeze_mutex vs. s_umount ordering established by\nbdev_{freeze,thaw}() and can thus ABBA against a concurrent block-layer\nfreeze even when the recursive path isn't hit.\n\nFix this by not holding s_umount around the bdev_thaw() loop at all. Pin\nthe superblock with an active reference instead as\nfilesystems_freeze_callback() does. The active reference keeps the\nsuperblock from being shut down and so ->s_bdev stays valid without\nholding s_umount. The block-layer-held freeze is dropped by\nfs_bdev_thaw() with FREEZE_MAY_NEST | FREEZE_HOLDER_USERSPACE exactly as\na regular unfreeze would and thaw_super_locked() handles\nfilesystem-level freezes as before.\n\nThe emergency thaw path has deadlocked like this in one form or\nanother for a long long time but the current exclusively-held\nshape dates back to commit [1] where thaw_bdev() already ended in\nthaw_super() with s_umount held by do_thaw_all_callback().","published":"2026-08-10T13:19:59.000Z","lastModified":"2026-08-23T13:16:33.000Z","status":"Received","sourceIdentifier":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","cvss":null,"cwe":[],"affected":[],"epss":{"score":0.00184,"percentile":0.07965,"date":"2026-10-27","history":[]},"kev":{"listed":false},"exploits":{"count":0,"verified":false,"firstPublished":null,"source":"Exploit-DB (https://gitlab.com/exploit-database/exploitdb)","entries":[]},"verdict":{"level":"unknown","text":"Not yet scored. NVD analysis is pending; check back once CVSS and EPSS values are published."},"changes":[],"references":[{"url":"https://git.kernel.org/stable/c/05536cad35f27b520d4b6f0e57c8cc5bfb6b0502","source":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/2a1127c1c58b4f15a93f2fd56ff7c2c3d611d5c5","source":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/4c483644d1a7709efe7d1be7dbf88cf4008a7864","source":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/63d78b546eefc38ad9898dc839bfc94811ede547","source":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/749d7aa0377aae32af8c0a4ad43371e7bf830ab5","source":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/96248aeddde794227a49af1a332a1e21b3c15d56","source":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/99719b5da9320ed344daee87d9c73d321a98f252","source":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/c202aa03388fd1889b7aa4f7d677c49e22cd9700","source":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"}],"sources":{"nvd":"https://nvd.nist.gov/vuln/detail/CVE-2026-68132","epss":"https://www.first.org/epss/","kev":"https://www.cisa.gov/known-exploited-vulnerabilities-catalog","exploitdb":"https://www.exploit-db.com/"},"licence":"CC BY 4.0 — link back to the CVE Explorer if you publish the results; upstream data remains subject to its own terms."}