{"id":"CVE-2026-64378","revision":"ee1be0391a074b0ca8c9149985e6871b","records":[{"revision":"ee1be0391a074b0ca8c9149985e6871b","observedAt":"2026-10-23T15:48:27.903+00:00","statement":{"source":"cve-program","id":"CVE-2026-64378","aliases":[],"title":"writeback: fix race between cgroup_writeback_umount() and inode_switch_wbs()","description":"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.","state":0,"publishedAt":"2026-07-25T08:50:29.006+00:00","modifiedAt":"2026-10-19T20:38:25.561+00:00","affected":[{"ecosystem":"Vendor product","name":"Linux","ranges":[],"versions":[],"rawVersionEvidence":"{\n                    \"product\": \"Linux\",\n                    \"vendor\": \"Linux\",\n                    \"defaultStatus\": \"unaffected\",\n                    \"repo\": \"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\",\n                    \"programFiles\": [\n                        \"fs/fs-writeback.c\"\n                    ],\n                    \"versions\": [\n                        {\n                            \"version\": \"a1a0e23e49037c23ea84bc8cc146a03584d13577\",\n                            \"lessThan\": \"087d5b8b501c570f84bf655164e6698c3ce146e0\",\n                            \"status\": \"affected\",\n                            \"versionType\": \"git\"\n                        },\n                        {\n                            \"version\": \"a1a0e23e49037c23ea84bc8cc146a03584d13577\",\n                            \"lessThan\": \"3c9c9648f77e4d14e50676bc51c2174ba9c8d361\",\n                            \"status\": \"affected\",\n                            \"versionType\": \"git\"\n                        },\n                        {\n                            \"version\": \"a1a0e23e49037c23ea84bc8cc146a03584d13577\",\n                            \"lessThan\": \"5c3265f3252b2ee50707adaaa3f9bd0df3df72de\",\n                            \"status\": \"affected\",\n                            \"versionType\": \"git\"\n                        },\n                        {\n                            \"version\": \"a1a0e23e49037c23ea84bc8cc146a03584d13577\",\n                            \"lessThan\": \"c923cc3cb5cd8945ceaf08252754110643446593\",\n                            \"status\": \"affected\",\n                            \"versionType\": \"git\"\n                        },\n                        {\n                            \"version\": \"a1a0e23e49037c23ea84bc8cc146a03584d13577\",\n                            \"lessThan\": \"685fc15a410885b6d4dee64de0dce721b9428b12\",\n                            \"status\": \"affected\",\n                            \"versionType\": \"git\"\n                        },\n                        {\n                            \"version\": \"a1a0e23e49037c23ea84bc8cc146a03584d13577\",\n                            \"lessThan\": \"53eeaf4d63068dbc7708b0c7adb20151c812feca\",\n                            \"status\": \"affected\",\n                            \"versionType\": \"git\"\n                        },\n                        {\n                            \"version\": \"a1a0e23e49037c23ea84bc8cc146a03584d13577\",\n                            \"lessThan\": \"cba38ec4cbd3a7b8b942a8d52531a05be8a9ff0d\",\n                            \"status\": \"affected\",\n                            \"versionType\": \"git\"\n                        },\n                        {\n                            \"version\": \"c5cbbec54fe71c4de2d34f8c0ec8fbfdd7f17339\",\n                            \"status\": \"affected\",\n                            \"versionType\": \"git\"\n                        },\n                        {\n                            \"version\": \"4.4.5\",\n                            \"lessThan\": \"4.5\",\n                            \"status\": \"affected\",\n                            \"versionType\": \"semver\"\n                        }\n                    ]\n                }"},{"ecosystem":"Vendor product","name":"Linux","ranges":[],"versions":[],"rawVersionEvidence":"{\n                    \"product\": \"Linux\",\n                    \"vendor\": \"Linux\",\n                    \"defaultStatus\": \"affected\",\n                    \"repo\": \"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\",\n                    \"programFiles\": [\n                        \"fs/fs-writeback.c\"\n                    ],\n                    \"versions\": [\n                        {\n                            \"version\": \"4.5\",\n                            \"status\": \"affected\"\n                        },\n                        {\n                            \"version\": \"0\",\n                            \"lessThan\": \"4.5\",\n                            \"status\": \"unaffected\",\n                            \"versionType\": \"semver\"\n                        },\n                        {\n                            \"version\": \"5.10.261\",\n                            \"lessThanOrEqual\": \"5.10.*\",\n                            \"status\": \"unaffected\",\n                            \"versionType\": \"semver\"\n                        },\n                        {\n                            \"version\": \"6.1.178\",\n                            \"lessThanOrEqual\": \"6.1.*\",\n                            \"status\": \"unaffected\",\n                            \"versionType\": \"semver\"\n                        },\n                        {\n                            \"version\": \"6.6.145\",\n                            \"lessThanOrEqual\": \"6.6.*\",\n                            \"status\": \"unaffected\",\n                            \"versionType\": \"semver\"\n                        },\n                        {\n                            \"version\": \"6.12.96\",\n                            \"lessThanOrEqual\": \"6.12.*\",\n                            \"status\": \"unaffected\",\n                            \"versionType\": \"semver\"\n                        },\n                        {\n                            \"version\": \"6.18.39\",\n                            \"lessThanOrEqual\": \"6.18.*\",\n                            \"status\": \"unaffected\",\n                            \"versionType\": \"semver\"\n                        },\n                        {\n                            \"version\": \"7.1.4\",\n                            \"lessThanOrEqual\": \"7.1.*\",\n                            \"status\": \"unaffected\",\n                            \"versionType\": \"semver\"\n                        },\n                        {\n                            \"version\": \"7.2\",\n                            \"lessThanOrEqual\": \"*\",\n                            \"status\": \"unaffected\",\n                            \"versionType\": \"original_commit_for_fix\"\n                        }\n                    ]\n                }"}],"metrics":[{"system":"CVSS 3.1","vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","score":7.8,"severity":"HIGH"}],"references":["https://git.kernel.org/stable/c/087d5b8b501c570f84bf655164e6698c3ce146e0","https://git.kernel.org/stable/c/3c9c9648f77e4d14e50676bc51c2174ba9c8d361","https://git.kernel.org/stable/c/5c3265f3252b2ee50707adaaa3f9bd0df3df72de","https://git.kernel.org/stable/c/c923cc3cb5cd8945ceaf08252754110643446593","https://git.kernel.org/stable/c/685fc15a410885b6d4dee64de0dce721b9428b12","https://git.kernel.org/stable/c/53eeaf4d63068dbc7708b0c7adb20151c812feca","https://git.kernel.org/stable/c/cba38ec4cbd3a7b8b942a8d52531a05be8a9ff0d"],"sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-64378","license":"CVE Program Terms of Use","key":"cve-program:CVE-2026-64378","identifiers":["CVE-2026-64378"]},"retained":false,"historicalAffected":[]}],"coverage":[]}