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          "lang": "en",
          "value": "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\u0027s 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(\u0026sbi-\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(\u0026sbi-\u003es_kobj)\n      kn = kobj-\u003esd              // stale pointer\n      kernfs_get(kn)             // UAF on freed kernfs_node\n                                   ext4_journal_destroy()\n                                     flush_work(\u0026sbi-\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."
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            "baseSeverity": "HIGH",
            "vectorString": "CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H",
            "version": "3.1"
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              "value": "AV:L - The vulnerable ext4 paths are reached through local filesystem operations such as mounting/unmounting an ext4 image, reading ext4 procfs state, or writing ext4 sysfs controls; there is no direct network packet path.\nAC:L - The race is between queued ext4 superblock error work and teardown, and a crafted/ext4-error scenario can repeatedly drive the work while unmount/cleanup proceeds; under the required rule, this attacker-influenced race is Low complexity.\nPR:N - Directly initiating mount/umount or sysfs error injection requires CAP_SYS_ADMIN in the initial namespace, but a highest-severity reasonable scenario is an attacker-supplied crafted ext4 filesystem image mounted/unmounted by a victim or privileged automounter, requiring no attacker privilege.\nUI:R - Exploitation in the no-attacker-privilege scenario requires a victim or privileged system component to mount and later unmount/process the malicious ext4 filesystem image.\nS:U - The corruption occurs inside the kernel filesystem/sysfs/kernfs lifetime management for the same host kernel security authority; it is not a VM escape or cross-authority boundary break.\nC:H - The bug is a use-after-free of a kernfs_node reached through sysfs_notify after kobject deletion, and kernel UAFs are treated as capable of enabling high-impact information disclosure.\nI:H - The stale kernfs_node is refcounted and used after free, giving a memory-corruption primitive that is defensibly treated as potentially exploitable for kernel control-flow or data modification.\nA:H - At minimum the UAF can crash or oops the kernel during ext4 unmount/error-work processing, causing high availability impact."
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