CVE-2026-64378: Software Security Vulnerability Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-325c-m2q7-75hg",
  "modified" : "2026-07-27T06:30:34Z",
  "published" : "2026-07-25T12:31:33Z",
  "aliases" : [ "CVE-2026-64378" ],
  "details" : "In the Linux kernel, the following vulnerability has been resolved:\n\nwriteback: fix race between cgroup_writeback_umount() and inode_switch_wbs()\n\nWhen a container exits, the following BUG_ON() is occasionally triggered:\n\n==================================================================\n VFS: Busy inodes after unmount of sdb (ext4)\n ------------[ cut here ]------------\n kernel BUG at fs/super.c:695!\n CPU: 3 PID: 6 Comm: containerd-shim Tainted: G OE K 6.6 #1\n pstate: 63400009 (nZCv daif +PAN -UAO +TCO +DIT -SSBS BTYPE=--)\n pc : generic_shutdown_super+0xf0/0x100\n lr : generic_shutdown_super+0xf0/0x100\n Call trace:\n  generic_shutdown_super+0xf0/0x100\n  kill_block_super+0x20/0x48\n  ext4_kill_sb+0x28/0x60\n  deactivate_locked_super+0x54/0x130\n  deactivate_super+0x84/0xa0\n  cleanup_mnt+0xa4/0x140\n  __cleanup_mnt+0x18/0x28\n  task_work_run+0x78/0xe0\n  do_notify_resume+0x204/0x240\n==================================================================\n\nThe root cause is a race between cgroup_writeback_umount() and\ninode_switch_wbs()/cleanup_offline_cgwb(). There is a window between\ninode_prepare_wbs_switch() returning true and the subsequent\nwb_queue_isw() call. Following is the process that triggers the issue:\n\n      CPU A (umount)           |          CPU B (writeback)\n~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~\n                                 inode_switch_wbs/cleanup_offline_cgwb\n                                  atomic_inc(&isw_nr_in_flight)\n                                  inode_prepare_wbs_switch\n                                   -> passes SB_ACTIVE check\n                                   __iget(inode)\n generic_shutdown_super\n  sb->s_flags &= ~SB_ACTIVE\n  cgroup_writeback_umount(sb)\n   smp_mb()\n   atomic_read(&isw_nr_in_flight)\n   rcu_barrier()\n    -> no pending RCU callbacks\n   flush_workqueue(isw_wq)\n    -> nothing queued, returns\n  evict_inodes(sb)\n   -> Inode skipped as isw still holds a ref.\n  sop->put_super(sb)\n   /* destroys percpu counters */\n  -> VFS: Busy inodes after unmount!\n                                  wb_queue_isw()\n                                   queue_work(isw_wq, ...)\n                                  /* later in work function */\n                                  inode_switch_wbs_work_fn\n                                   process_inode_switch_wbs\n                                    iput() -> evict\n                                     percpu_counter_dec() // UAF!\n\nFix this by extending the RCU read-side critical section in\ninode_switch_wbs() and cleanup_offline_cgwb() to cover from\ninode_prepare_wbs_switch() through wb_queue_isw().  Since there is\nno sleep in this window, rcu_read_lock() can be used.  Then add a\nsynchronize_rcu() in cgroup_writeback_umount() before the existing\nrcu_barrier(), so that all in-flight switchers that have passed the\nSB_ACTIVE check have completed queue_work() before flush_workqueue()\nis called.\n\nThe existing rcu_barrier() is intentionally retained so this fix can\nbe backported unchanged to stable kernels (5.10.y, 6.6.y, ...) that\nstill queue switches via queue_rcu_work(). It is a no-op on current\nmainline (since commit e1b849cfa6b6 (\"writeback: Avoid contention on\nwb->list_lock when switching inodes\")) and is removed in a follow-up\npatch.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H"
  } ],
  "affected" : [ ],
  "references" : [ {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-64378"
  }, {
    "type" : "WEB",
    "url" : "https://git.kernel.org/stable/c/087d5b8b501c570f84bf655164e6698c3ce146e0"
  }, {
    "type" : "WEB",
    "url" : "https://git.kernel.org/stable/c/3c9c9648f77e4d14e50676bc51c2174ba9c8d361"
  }, {
    "type" : "WEB",
    "url" : "https://git.kernel.org/stable/c/53eeaf4d63068dbc7708b0c7adb20151c812feca"
  }, {
    "type" : "WEB",
    "url" : "https://git.kernel.org/stable/c/5c3265f3252b2ee50707adaaa3f9bd0df3df72de"
  }, {
    "type" : "WEB",
    "url" : "https://git.kernel.org/stable/c/685fc15a410885b6d4dee64de0dce721b9428b12"
  }, {
    "type" : "WEB",
    "url" : "https://git.kernel.org/stable/c/c923cc3cb5cd8945ceaf08252754110643446593"
  }, {
    "type" : "WEB",
    "url" : "https://git.kernel.org/stable/c/cba38ec4cbd3a7b8b942a8d52531a05be8a9ff0d"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-362" ],
    "severity" : "HIGH",
    "github_reviewed" : false,
    "github_reviewed_at" : null,
    "nvd_published_at" : "2026-07-25T10:17:20Z"
  }
}