{ "dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": { "cveId": "CVE-2026-64378", "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "state": "PUBLISHED", "assignerShortName": "Linux", "dateReserved": "2026-07-19T15:36:31.784Z", "datePublished": "2026-07-25T08:50:29.006Z", "dateUpdated": "2026-08-17T04:54:29.511Z" }, "containers": { "cna": { "providerMetadata": { "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "shortName": "Linux", "dateUpdated": "2026-08-17T04:54:29.511Z" }, "descriptions": [ { "lang": "en", "value": "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." } ], "metrics": [ { "cvssV3_1": { "version": "3.1", "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H", "baseScore": 7.8, "baseSeverity": "HIGH" }, "scenarios": [ { "lang": "en", "value": "AV:L - The vulnerability is reached through local filesystem writes, cgroup teardown, and mount-namespace or filesystem unmount paths; no network protocol directly reaches the race.\nAC:L - An attacker can churn cgroup writeback switches while repeatedly triggering container or mount teardown, controlling both racing activities and amplifying the timing window.\nPR:L - A basic local or container user can dirty writable files and initiate its own cgroup or namespace teardown; lifecycle infrastructure can perform the privileged final unmount automatically.\nUI:N - The attacker can generate the writeback state and trigger teardown without requiring another user to perform an action.\nS:U - The resulting corruption affects the same host kernel security authority and does not inherently cross a VM or hardware isolation boundary.\nC:H - The delayed worker can access superblock-private state after it and its per-CPU counters have been freed, creating an exploitable use-after-free capable of exposing arbitrary kernel memory.\nI:H - The freed superblock and per-CPU counter pointers are subsequently dereferenced and modified, potentially providing attacker-influenced kernel writes and control-flow hijacking.\nA:H - The race demonstrably triggers the busy-inode BUG_ON, and configurations continuing past that check encounter a use-after-free capable of causing an oops or kernel panic." } ] } ], "affected": [ { "product": "Linux", "vendor": "Linux", "defaultStatus": "unaffected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": [ "fs/fs-writeback.c" ], "versions": [ { "version": "a1a0e23e49037c23ea84bc8cc146a03584d13577", "lessThan": "087d5b8b501c570f84bf655164e6698c3ce146e0", "status": "affected", "versionType": "git" }, { "version": "a1a0e23e49037c23ea84bc8cc146a03584d13577", "lessThan": "3c9c9648f77e4d14e50676bc51c2174ba9c8d361", "status": "affected", "versionType": "git" }, { "version": "a1a0e23e49037c23ea84bc8cc146a03584d13577", "lessThan": "5c3265f3252b2ee50707adaaa3f9bd0df3df72de", "status": "affected", "versionType": "git" }, { "version": "a1a0e23e49037c23ea84bc8cc146a03584d13577", "lessThan": "c923cc3cb5cd8945ceaf08252754110643446593", "status": "affected", "versionType": "git" }, { "version": "a1a0e23e49037c23ea84bc8cc146a03584d13577", "lessThan": "685fc15a410885b6d4dee64de0dce721b9428b12", "status": "affected", "versionType": "git" }, { "version": "a1a0e23e49037c23ea84bc8cc146a03584d13577", "lessThan": "53eeaf4d63068dbc7708b0c7adb20151c812feca", "status": "affected", "versionType": "git" }, { "version": "a1a0e23e49037c23ea84bc8cc146a03584d13577", "lessThan": "cba38ec4cbd3a7b8b942a8d52531a05be8a9ff0d", "status": "affected", "versionType": "git" }, { "version": "c5cbbec54fe71c4de2d34f8c0ec8fbfdd7f17339", "status": "affected", "versionType": "git" }, { "version": "4.4.5", "lessThan": "4.5", "status": "affected", "versionType": "semver" } ] }, { "product": "Linux", "vendor": "Linux", "defaultStatus": "affected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": [ "fs/fs-writeback.c" ], "versions": [ { "version": "4.5", "status": "affected" }, { "version": "0", "lessThan": "4.5", "status": "unaffected", "versionType": "semver" }, { "version": "5.10.261", "lessThanOrEqual": "5.10.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.1.178", "lessThanOrEqual": "6.1.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.6.145", "lessThanOrEqual": "6.6.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.12.96", "lessThanOrEqual": "6.12.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.18.39", "lessThanOrEqual": "6.18.*", "status": "unaffected", "versionType": "semver" }, { "version": "7.1.4", "lessThanOrEqual": "7.1.*", "status": "unaffected", "versionType": "semver" }, { "version": "7.2", "lessThanOrEqual": "*", "status": "unaffected", "versionType": "original_commit_for_fix" } ] } ], "cpeApplicability": [ { "nodes": [ { "operator": "OR", "negate": false, "cpeMatch": [ { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "4.5", "versionEndExcluding": "5.10.261" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "4.5", "versionEndExcluding": "6.1.178" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "4.5", "versionEndExcluding": "6.6.145" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "4.5", "versionEndExcluding": "6.12.96" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "4.5", "versionEndExcluding": "6.18.39" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "4.5", "versionEndExcluding": "7.1.4" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "4.5", "versionEndExcluding": "7.2" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "4.4.5" } ] } ] } ], "references": [ { "url": "https://git.kernel.org/stable/c/087d5b8b501c570f84bf655164e6698c3ce146e0" }, { "url": "https://git.kernel.org/stable/c/3c9c9648f77e4d14e50676bc51c2174ba9c8d361" }, { "url": "https://git.kernel.org/stable/c/5c3265f3252b2ee50707adaaa3f9bd0df3df72de" }, { "url": "https://git.kernel.org/stable/c/c923cc3cb5cd8945ceaf08252754110643446593" }, { "url": "https://git.kernel.org/stable/c/685fc15a410885b6d4dee64de0dce721b9428b12" }, { "url": "https://git.kernel.org/stable/c/53eeaf4d63068dbc7708b0c7adb20151c812feca" }, { "url": "https://git.kernel.org/stable/c/cba38ec4cbd3a7b8b942a8d52531a05be8a9ff0d" } ], "title": "writeback: fix race between cgroup_writeback_umount() and inode_switch_wbs()", "x_generator": { "engine": "bippy-1.2.0" } } } }