{"id":"CVE-2026-68132","summary":"super: fix emergency thaw deadlock on frozen block devices","details":"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-\u003es_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-\u003es_umount\n    bdev_thaw(sb-\u003es_bdev)\n      mutex_lock(&bdev-\u003ebd_fsfreeze_mutex)\n      # bd_fsfreeze_count drops 1 -\u003e 0\n      bd_holder_ops-\u003ethaw == fs_bdev_thaw\n        get_bdev_super(bdev)\n          bdev_super_lock(bdev, true)\n            super_lock(sb, true)\n              down_write(&sb-\u003es_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]  \u003cTASK\u003e\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]  \u003c/TASK\u003e\n\nbdev_super_lock() even documents the violated requirement with\nlockdep_assert_not_held(&sb-\u003es_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 -\u003es_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().","modified":"2026-08-25T03:30:11.460297767Z","published":"2026-08-10T11:58:55.196Z","database_specific":{"cna_assigner":"Linux","osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/68xxx/CVE-2026-68132.json"},"references":[{"type":"WEB","url":"https://git.kernel.org/stable/c/05536cad35f27b520d4b6f0e57c8cc5bfb6b0502"},{"type":"WEB","url":"https://git.kernel.org/stable/c/2a1127c1c58b4f15a93f2fd56ff7c2c3d611d5c5"},{"type":"WEB","url":"https://git.kernel.org/stable/c/4c483644d1a7709efe7d1be7dbf88cf4008a7864"},{"type":"WEB","url":"https://git.kernel.org/stable/c/63d78b546eefc38ad9898dc839bfc94811ede547"},{"type":"WEB","url":"https://git.kernel.org/stable/c/749d7aa0377aae32af8c0a4ad43371e7bf830ab5"},{"type":"WEB","url":"https://git.kernel.org/stable/c/96248aeddde794227a49af1a332a1e21b3c15d56"},{"type":"WEB","url":"https://git.kernel.org/stable/c/99719b5da9320ed344daee87d9c73d321a98f252"},{"type":"WEB","url":"https://git.kernel.org/stable/c/c202aa03388fd1889b7aa4f7d677c49e22cd9700"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/68xxx/CVE-2026-68132.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-68132"},{"type":"PACKAGE","url":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","events":[{"introduced":"08fdc8a0138afaf324296a342f32ad26ec465e43"},{"fixed":"96248aeddde794227a49af1a332a1e21b3c15d56"},{"fixed":"c202aa03388fd1889b7aa4f7d677c49e22cd9700"},{"fixed":"2a1127c1c58b4f15a93f2fd56ff7c2c3d611d5c5"},{"fixed":"05536cad35f27b520d4b6f0e57c8cc5bfb6b0502"},{"fixed":"99719b5da9320ed344daee87d9c73d321a98f252"},{"fixed":"63d78b546eefc38ad9898dc839bfc94811ede547"},{"fixed":"4c483644d1a7709efe7d1be7dbf88cf4008a7864"},{"fixed":"749d7aa0377aae32af8c0a4ad43371e7bf830ab5"}]}],"database_specific":{"source":"https://storage.googleapis.com/osv-test-cve-osv-conversion/osv-output/CVE-2026-68132.json"}},{"package":{"name":"Kernel","ecosystem":"Linux"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"4.17.0"},{"fixed":"5.10.266"}]},{"type":"ECOSYSTEM","events":[{"introduced":"5.11.0"},{"fixed":"5.15.217"}]},{"type":"ECOSYSTEM","events":[{"introduced":"5.16.0"},{"fixed":"6.1.184"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.2.0"},{"fixed":"6.6.153"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.7.0"},{"fixed":"6.12.105"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.13.0"},{"fixed":"6.18.42"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.19.0"},{"fixed":"7.1.6"}]}],"database_specific":{"source":"https://storage.googleapis.com/osv-test-cve-osv-conversion/osv-output/CVE-2026-68132.json"}}],"schema_version":"1.9.0"}