{"id":"AZL-83282","summary":"CVE-2026-31446 affecting package kernel for versions less than 6.6.134.1-2","details":"In the Linux kernel, the following vulnerability has been resolved:\n\next4: fix use-after-free in update_super_work when racing with umount\n\nCommit b98535d09179 (\"ext4: fix bug_on in start_this_handle during umount\nfilesystem\") moved ext4_unregister_sysfs() before flushing s_sb_upd_work\nto prevent new error work from being queued via /proc/fs/ext4/xx/mb_groups\nreads during unmount. However, this introduced a use-after-free because\nupdate_super_work calls ext4_notify_error_sysfs() -\u003e sysfs_notify() which\naccesses the kobject's kernfs_node after it has been freed by kobject_del()\nin ext4_unregister_sysfs():\n\n  update_super_work                ext4_put_super\n  -----------------                --------------\n                                   ext4_unregister_sysfs(sb)\n                                     kobject_del(&sbi-\u003es_kobj)\n                                       __kobject_del()\n                                         sysfs_remove_dir()\n                                           kobj-\u003esd = NULL\n                                         sysfs_put(sd)\n                                           kernfs_put()  // RCU free\n  ext4_notify_error_sysfs(sbi)\n    sysfs_notify(&sbi-\u003es_kobj)\n      kn = kobj-\u003esd              // stale pointer\n      kernfs_get(kn)             // UAF on freed kernfs_node\n                                   ext4_journal_destroy()\n                                     flush_work(&sbi-\u003es_sb_upd_work)\n\nInstead of reordering the teardown sequence, fix this by making\next4_notify_error_sysfs() detect that sysfs has already been torn down\nby checking s_kobj.state_in_sysfs, and skipping the sysfs_notify() call\nin that case. A dedicated mutex (s_error_notify_mutex) serializes\next4_notify_error_sysfs() against kobject_del() in ext4_unregister_sysfs()\nto prevent TOCTOU races where the kobject could be deleted between the\nstate_in_sysfs check and the sysfs_notify() call.","modified":"2026-08-28T17:47:43.646308215Z","published":"2026-04-22T14:16:38Z","upstream":["CVE-2026-31446"],"references":[{"type":"WEB","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-31446"}],"affected":[{"package":{"name":"kernel","ecosystem":"Azure Linux:3","purl":"pkg:rpm/azure-linux/kernel"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"6.6.134.1-2"}]}],"database_specific":{"source":"https://github.com/microsoft/AzureLinuxVulnerabilityData/blob/main/osv/AZL-83282.json"}}],"schema_version":"1.9.0"}