{"api_version":"1","generated_at":"2026-05-13T02:24:20+00:00","cve":"CVE-2024-56672","urls":{"html":"https://cve.report/CVE-2024-56672","api":"https://cve.report/api/cve/CVE-2024-56672.json","docs":"https://cve.report/api","cve_org":"https://www.cve.org/CVERecord?id=CVE-2024-56672","nvd":"https://nvd.nist.gov/vuln/detail/CVE-2024-56672"},"summary":{"title":"blk-cgroup: Fix UAF in blkcg_unpin_online()","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nblk-cgroup: Fix UAF in blkcg_unpin_online()\n\nblkcg_unpin_online() walks up the blkcg hierarchy putting the online pin. To\nwalk up, it uses blkcg_parent(blkcg) but it was calling that after\nblkcg_destroy_blkgs(blkcg) which could free the blkcg, leading to the\nfollowing UAF:\n\n  ==================================================================\n  BUG: KASAN: slab-use-after-free in blkcg_unpin_online+0x15a/0x270\n  Read of size 8 at addr ffff8881057678c0 by task kworker/9:1/117\n\n  CPU: 9 UID: 0 PID: 117 Comm: kworker/9:1 Not tainted 6.13.0-rc1-work-00182-gb8f52214c61a-dirty #48\n  Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS unknown 02/02/2022\n  Workqueue: cgwb_release cgwb_release_workfn\n  Call Trace:\n   <TASK>\n   dump_stack_lvl+0x27/0x80\n   print_report+0x151/0x710\n   kasan_report+0xc0/0x100\n   blkcg_unpin_online+0x15a/0x270\n   cgwb_release_workfn+0x194/0x480\n   process_scheduled_works+0x71b/0xe20\n   worker_thread+0x82a/0xbd0\n   kthread+0x242/0x2c0\n   ret_from_fork+0x33/0x70\n   ret_from_fork_asm+0x1a/0x30\n   </TASK>\n  ...\n  Freed by task 1944:\n   kasan_save_track+0x2b/0x70\n   kasan_save_free_info+0x3c/0x50\n   __kasan_slab_free+0x33/0x50\n   kfree+0x10c/0x330\n   css_free_rwork_fn+0xe6/0xb30\n   process_scheduled_works+0x71b/0xe20\n   worker_thread+0x82a/0xbd0\n   kthread+0x242/0x2c0\n   ret_from_fork+0x33/0x70\n   ret_from_fork_asm+0x1a/0x30\n\nNote that the UAF is not easy to trigger as the free path is indirected\nbehind a couple RCU grace periods and a work item execution. I could only\ntrigger it with artifical msleep() injected in blkcg_unpin_online().\n\nFix it by reading the parent pointer before destroying the blkcg's blkg's.","state":"PUBLISHED","assigner":"Linux","published_at":"2024-12-27 15:15:27","updated_at":"2026-05-12 13:16:22"},"problem_types":["CWE-416","CWE-416 CWE-416 Use After Free"],"metrics":[{"version":"3.1","source":"nvd@nist.gov","type":"Primary","score":"7","severity":"HIGH","vector":"CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H","data":{"version":"3.1","vectorString":"CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H","baseScore":7,"baseSeverity":"HIGH","attackVector":"LOCAL","attackComplexity":"HIGH","privilegesRequired":"LOW","userInteraction":"NONE","scope":"UNCHANGED","confidentialityImpact":"HIGH","integrityImpact":"HIGH","availabilityImpact":"HIGH"}},{"version":"3.1","source":"ADP","type":"DECLARED","score":"7.8","severity":"HIGH","vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","data":{"attackComplexity":"LOW","attackVector":"LOCAL","availabilityImpact":"HIGH","baseScore":7.8,"baseSeverity":"HIGH","confidentialityImpact":"HIGH","integrityImpact":"HIGH","privilegesRequired":"LOW","scope":"UNCHANGED","userInteraction":"NONE","vectorString":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","version":"3.1"}},{"version":"3.1","source":"134c704f-9b21-4f2e-91b3-4a467353bcc0","type":"Secondary","score":"7.8","severity":"HIGH","vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","data":{"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","attackVector":"LOCAL","attackComplexity":"LOW","privilegesRequired":"LOW","userInteraction":"NONE","scope":"UNCHANGED","confidentialityImpact":"HIGH","integrityImpact":"HIGH","availabilityImpact":"HIGH"}}],"references":[{"url":"https://git.kernel.org/stable/c/8a07350fe070017a887433f4d6909433955be5f1","name":"https://git.kernel.org/stable/c/8a07350fe070017a887433f4d6909433955be5f1","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/29d1e06560f0f6179062ac638b4064deb637d1ad","name":"https://git.kernel.org/stable/c/29d1e06560f0f6179062ac638b4064deb637d1ad","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":["Patch"],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://lists.debian.org/debian-lts-announce/2025/03/msg00002.html","name":"https://lists.debian.org/debian-lts-announce/2025/03/msg00002.html","refsource":"af854a3a-2127-422b-91ae-364da2661108","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/83f5a87ee8caa76a917f59912a74d6811f773c67","name":"https://git.kernel.org/stable/c/83f5a87ee8caa76a917f59912a74d6811f773c67","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/64afc6fe24c9896c0153e5a199bcea241ecb0d5c","name":"https://git.kernel.org/stable/c/64afc6fe24c9896c0153e5a199bcea241ecb0d5c","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":["Patch"],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://cert-portal.siemens.com/productcert/html/ssa-265688.html","name":"https://cert-portal.siemens.com/productcert/html/ssa-265688.html","refsource":"0b142b55-0307-4c5a-b3c9-f314f3fb7c5e","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/5baa28569c924d9a90d036c2aaab79f791fedaf8","name":"https://git.kernel.org/stable/c/5baa28569c924d9a90d036c2aaab79f791fedaf8","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":["Patch"],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/86e6ca55b83c575ab0f2e105cf08f98e58d3d7af","name":"https://git.kernel.org/stable/c/86e6ca55b83c575ab0f2e105cf08f98e58d3d7af","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":["Patch"],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://lists.debian.org/debian-lts-announce/2025/03/msg00001.html","name":"https://lists.debian.org/debian-lts-announce/2025/03/msg00001.html","refsource":"af854a3a-2127-422b-91ae-364da2661108","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://www.cve.org/CVERecord?id=CVE-2024-56672","name":"CVE Program record","refsource":"CVE.ORG","tags":["canonical"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2024-56672","name":"NVD vulnerability detail","refsource":"NVD","tags":["canonical","analysis"]}],"affected":[{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 4308a434e5e08c78676aa66bc626ef78cbef0883 83f5a87ee8caa76a917f59912a74d6811f773c67 git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 4308a434e5e08c78676aa66bc626ef78cbef0883 8a07350fe070017a887433f4d6909433955be5f1 git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 4308a434e5e08c78676aa66bc626ef78cbef0883 64afc6fe24c9896c0153e5a199bcea241ecb0d5c git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 4308a434e5e08c78676aa66bc626ef78cbef0883 5baa28569c924d9a90d036c2aaab79f791fedaf8 git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 4308a434e5e08c78676aa66bc626ef78cbef0883 29d1e06560f0f6179062ac638b4064deb637d1ad git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 4308a434e5e08c78676aa66bc626ef78cbef0883 86e6ca55b83c575ab0f2e105cf08f98e58d3d7af git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 5.7","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 5.7 semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 5.10.234 5.10.* semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 5.15.177 5.15.* semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 6.1.121 6.1.* semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 6.6.67 6.6.* semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 6.12.6 6.12.* semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 6.13 * original_commit_for_fix","platforms":[]},{"source":"ADP","vendor":"Siemens","product":"SIMATIC S7-1500 TM MFP - GNU/Linux subsystem","version":"affected * custom","platforms":[]}],"timeline":[],"solutions":[],"workarounds":[],"exploits":[],"credits":[],"nvd_cpes":[{"cve_year":"2024","cve_id":"56672","vulnerable":"1","versionEndIncluding":"","cpe1":"cpe","cpe2":"2.3","cpe3":"o","cpe4":"linux","cpe5":"linux_kernel","cpe6":"*","cpe7":"*","cpe8":"*","cpe9":"*","cpe10":"*","cpe11":"*","cpe12":"*","cpe13":"*"}],"vendor_comments":[],"enrichments":{"kev":null,"epss":null,"legacy_qids":[]},"source_records":{"cve_program":{"containers":{"adp":[{"metrics":[{"cvssV3_1":{"attackComplexity":"LOW","attackVector":"LOCAL","availabilityImpact":"HIGH","baseScore":7.8,"baseSeverity":"HIGH","confidentialityImpact":"HIGH","integrityImpact":"HIGH","privilegesRequired":"LOW","scope":"UNCHANGED","userInteraction":"NONE","vectorString":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","version":"3.1"}},{"other":{"content":{"id":"CVE-2024-56672","options":[{"Exploitation":"none"},{"Automatable":"no"},{"Technical Impact":"total"}],"role":"CISA Coordinator","timestamp":"2025-02-10T17:12:31.915249Z","version":"2.0.3"},"type":"ssvc"}}],"problemTypes":[{"descriptions":[{"cweId":"CWE-416","description":"CWE-416 Use After Free","lang":"en","type":"CWE"}]}],"providerMetadata":{"dateUpdated":"2025-02-10T17:21:07.331Z","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","shortName":"CISA-ADP"},"title":"CISA ADP Vulnrichment"},{"providerMetadata":{"dateUpdated":"2025-11-03T20:52:20.150Z","orgId":"af854a3a-2127-422b-91ae-364da2661108","shortName":"CVE"},"references":[{"url":"https://lists.debian.org/debian-lts-announce/2025/03/msg00001.html"},{"url":"https://lists.debian.org/debian-lts-announce/2025/03/msg00002.html"}],"title":"CVE Program Container"},{"affected":[{"defaultStatus":"unknown","product":"SIMATIC S7-1500 TM MFP - GNU/Linux subsystem","vendor":"Siemens","versions":[{"lessThan":"*","status":"affected","version":"0","versionType":"custom"}]}],"providerMetadata":{"dateUpdated":"2026-05-12T12:01:24.932Z","orgId":"0b142b55-0307-4c5a-b3c9-f314f3fb7c5e","shortName":"siemens-SADP"},"references":[{"url":"https://cert-portal.siemens.com/productcert/html/ssa-265688.html"}],"x_adpType":"supplier"}],"cna":{"affected":[{"defaultStatus":"unaffected","product":"Linux","programFiles":["block/blk-cgroup.c"],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","vendor":"Linux","versions":[{"lessThan":"83f5a87ee8caa76a917f59912a74d6811f773c67","status":"affected","version":"4308a434e5e08c78676aa66bc626ef78cbef0883","versionType":"git"},{"lessThan":"8a07350fe070017a887433f4d6909433955be5f1","status":"affected","version":"4308a434e5e08c78676aa66bc626ef78cbef0883","versionType":"git"},{"lessThan":"64afc6fe24c9896c0153e5a199bcea241ecb0d5c","status":"affected","version":"4308a434e5e08c78676aa66bc626ef78cbef0883","versionType":"git"},{"lessThan":"5baa28569c924d9a90d036c2aaab79f791fedaf8","status":"affected","version":"4308a434e5e08c78676aa66bc626ef78cbef0883","versionType":"git"},{"lessThan":"29d1e06560f0f6179062ac638b4064deb637d1ad","status":"affected","version":"4308a434e5e08c78676aa66bc626ef78cbef0883","versionType":"git"},{"lessThan":"86e6ca55b83c575ab0f2e105cf08f98e58d3d7af","status":"affected","version":"4308a434e5e08c78676aa66bc626ef78cbef0883","versionType":"git"}]},{"defaultStatus":"affected","product":"Linux","programFiles":["block/blk-cgroup.c"],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","vendor":"Linux","versions":[{"status":"affected","version":"5.7"},{"lessThan":"5.7","status":"unaffected","version":"0","versionType":"semver"},{"lessThanOrEqual":"5.10.*","status":"unaffected","version":"5.10.234","versionType":"semver"},{"lessThanOrEqual":"5.15.*","status":"unaffected","version":"5.15.177","versionType":"semver"},{"lessThanOrEqual":"6.1.*","status":"unaffected","version":"6.1.121","versionType":"semver"},{"lessThanOrEqual":"6.6.*","status":"unaffected","version":"6.6.67","versionType":"semver"},{"lessThanOrEqual":"6.12.*","status":"unaffected","version":"6.12.6","versionType":"semver"},{"lessThanOrEqual":"*","status":"unaffected","version":"6.13","versionType":"original_commit_for_fix"}]}],"cpeApplicability":[{"nodes":[{"cpeMatch":[{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"5.10.234","versionStartIncluding":"5.7","vulnerable":true},{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"5.15.177","versionStartIncluding":"5.7","vulnerable":true},{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"6.1.121","versionStartIncluding":"5.7","vulnerable":true},{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"6.6.67","versionStartIncluding":"5.7","vulnerable":true},{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"6.12.6","versionStartIncluding":"5.7","vulnerable":true},{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"6.13","versionStartIncluding":"5.7","vulnerable":true}],"negate":false,"operator":"OR"}]}],"descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\nblk-cgroup: Fix UAF in blkcg_unpin_online()\n\nblkcg_unpin_online() walks up the blkcg hierarchy putting the online pin. To\nwalk up, it uses blkcg_parent(blkcg) but it was calling that after\nblkcg_destroy_blkgs(blkcg) which could free the blkcg, leading to the\nfollowing UAF:\n\n  ==================================================================\n  BUG: KASAN: slab-use-after-free in blkcg_unpin_online+0x15a/0x270\n  Read of size 8 at addr ffff8881057678c0 by task kworker/9:1/117\n\n  CPU: 9 UID: 0 PID: 117 Comm: kworker/9:1 Not tainted 6.13.0-rc1-work-00182-gb8f52214c61a-dirty #48\n  Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS unknown 02/02/2022\n  Workqueue: cgwb_release cgwb_release_workfn\n  Call Trace:\n   <TASK>\n   dump_stack_lvl+0x27/0x80\n   print_report+0x151/0x710\n   kasan_report+0xc0/0x100\n   blkcg_unpin_online+0x15a/0x270\n   cgwb_release_workfn+0x194/0x480\n   process_scheduled_works+0x71b/0xe20\n   worker_thread+0x82a/0xbd0\n   kthread+0x242/0x2c0\n   ret_from_fork+0x33/0x70\n   ret_from_fork_asm+0x1a/0x30\n   </TASK>\n  ...\n  Freed by task 1944:\n   kasan_save_track+0x2b/0x70\n   kasan_save_free_info+0x3c/0x50\n   __kasan_slab_free+0x33/0x50\n   kfree+0x10c/0x330\n   css_free_rwork_fn+0xe6/0xb30\n   process_scheduled_works+0x71b/0xe20\n   worker_thread+0x82a/0xbd0\n   kthread+0x242/0x2c0\n   ret_from_fork+0x33/0x70\n   ret_from_fork_asm+0x1a/0x30\n\nNote that the UAF is not easy to trigger as the free path is indirected\nbehind a couple RCU grace periods and a work item execution. I could only\ntrigger it with artifical msleep() injected in blkcg_unpin_online().\n\nFix it by reading the parent pointer before destroying the blkcg's blkg's."}],"providerMetadata":{"dateUpdated":"2026-05-11T20:57:01.673Z","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","shortName":"Linux"},"references":[{"url":"https://git.kernel.org/stable/c/83f5a87ee8caa76a917f59912a74d6811f773c67"},{"url":"https://git.kernel.org/stable/c/8a07350fe070017a887433f4d6909433955be5f1"},{"url":"https://git.kernel.org/stable/c/64afc6fe24c9896c0153e5a199bcea241ecb0d5c"},{"url":"https://git.kernel.org/stable/c/5baa28569c924d9a90d036c2aaab79f791fedaf8"},{"url":"https://git.kernel.org/stable/c/29d1e06560f0f6179062ac638b4064deb637d1ad"},{"url":"https://git.kernel.org/stable/c/86e6ca55b83c575ab0f2e105cf08f98e58d3d7af"}],"title":"blk-cgroup: Fix UAF in blkcg_unpin_online()","x_generator":{"engine":"bippy-1.2.0"}}},"cveMetadata":{"assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","assignerShortName":"Linux","cveId":"CVE-2024-56672","datePublished":"2024-12-27T15:06:33.358Z","dateReserved":"2024-12-27T15:00:39.845Z","dateUpdated":"2026-05-12T12:01:24.932Z","state":"PUBLISHED"},"dataType":"CVE_RECORD","dataVersion":"5.2"},"nvd":{"publishedDate":"2024-12-27 15:15:27","lastModifiedDate":"2026-05-12 13:16:22","problem_types":["CWE-416","CWE-416 CWE-416 Use After Free"],"metrics":{"cvssMetricV31":[{"source":"nvd@nist.gov","type":"Primary","cvssData":{"version":"3.1","vectorString":"CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H","baseScore":7,"baseSeverity":"HIGH","attackVector":"LOCAL","attackComplexity":"HIGH","privilegesRequired":"LOW","userInteraction":"NONE","scope":"UNCHANGED","confidentialityImpact":"HIGH","integrityImpact":"HIGH","availabilityImpact":"HIGH"},"exploitabilityScore":1,"impactScore":5.9},{"source":"134c704f-9b21-4f2e-91b3-4a467353bcc0","type":"Secondary","cvssData":{"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","attackVector":"LOCAL","attackComplexity":"LOW","privilegesRequired":"LOW","userInteraction":"NONE","scope":"UNCHANGED","confidentialityImpact":"HIGH","integrityImpact":"HIGH","availabilityImpact":"HIGH"},"exploitabilityScore":1.8,"impactScore":5.9}]},"configurations":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.7","versionEndExcluding":"6.1.121","matchCriteriaId":"DA13D8C8-4561-4F7A-8047-DAD1CB2DABD7"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.2","versionEndExcluding":"6.6.67","matchCriteriaId":"BF4F2CD1-2CA6-4D6B-9B0C-57C3C4D6544A"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.7","versionEndExcluding":"6.12.6","matchCriteriaId":"0CB1A9BB-F95E-43DD-A2FD-147912FD91E5"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:6.13:rc1:*:*:*:*:*:*","matchCriteriaId":"62567B3C-6CEE-46D0-BC2E-B3717FBF7D13"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:6.13:rc2:*:*:*:*:*:*","matchCriteriaId":"5A073481-106D-4B15-B4C7-FB0213B8E1D4"}]}]}]},"legacy_mitre":{"record":{"CveYear":"2024","CveId":"56672","Ordinal":"1","Title":"blk-cgroup: Fix UAF in blkcg_unpin_online()","CVE":"CVE-2024-56672","Year":"2024"},"notes":[{"CveYear":"2024","CveId":"56672","Ordinal":"1","NoteData":"In the Linux kernel, the following vulnerability has been resolved:\n\nblk-cgroup: Fix UAF in blkcg_unpin_online()\n\nblkcg_unpin_online() walks up the blkcg hierarchy putting the online pin. To\nwalk up, it uses blkcg_parent(blkcg) but it was calling that after\nblkcg_destroy_blkgs(blkcg) which could free the blkcg, leading to the\nfollowing UAF:\n\n  ==================================================================\n  BUG: KASAN: slab-use-after-free in blkcg_unpin_online+0x15a/0x270\n  Read of size 8 at addr ffff8881057678c0 by task kworker/9:1/117\n\n  CPU: 9 UID: 0 PID: 117 Comm: kworker/9:1 Not tainted 6.13.0-rc1-work-00182-gb8f52214c61a-dirty #48\n  Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS unknown 02/02/2022\n  Workqueue: cgwb_release cgwb_release_workfn\n  Call Trace:\n   <TASK>\n   dump_stack_lvl+0x27/0x80\n   print_report+0x151/0x710\n   kasan_report+0xc0/0x100\n   blkcg_unpin_online+0x15a/0x270\n   cgwb_release_workfn+0x194/0x480\n   process_scheduled_works+0x71b/0xe20\n   worker_thread+0x82a/0xbd0\n   kthread+0x242/0x2c0\n   ret_from_fork+0x33/0x70\n   ret_from_fork_asm+0x1a/0x30\n   </TASK>\n  ...\n  Freed by task 1944:\n   kasan_save_track+0x2b/0x70\n   kasan_save_free_info+0x3c/0x50\n   __kasan_slab_free+0x33/0x50\n   kfree+0x10c/0x330\n   css_free_rwork_fn+0xe6/0xb30\n   process_scheduled_works+0x71b/0xe20\n   worker_thread+0x82a/0xbd0\n   kthread+0x242/0x2c0\n   ret_from_fork+0x33/0x70\n   ret_from_fork_asm+0x1a/0x30\n\nNote that the UAF is not easy to trigger as the free path is indirected\nbehind a couple RCU grace periods and a work item execution. I could only\ntrigger it with artifical msleep() injected in blkcg_unpin_online().\n\nFix it by reading the parent pointer before destroying the blkcg's blkg's.","Type":"Description","Title":"blk-cgroup: Fix UAF in blkcg_unpin_online()"}]}}}