{ "affected": [ { "ranges": [ { "events": [ { "introduced": "0e94682b73bfa6c44c98af7a26771c9c08c055d5" }, { "fixed": "03dc070fa0fc3cb4068693f468ccd5f8a7e58282" }, { "fixed": "d4352c0709bfd38c752fccbde7fd72a82ac78f23" }, { "fixed": "a5b98009f16d8a5fb4a8ff9a193f5735515c38fa" } ], "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "type": "GIT" } ] }, { "package": { "ecosystem": "Linux", "name": "Kernel" }, "ranges": [ { "events": [ { "introduced": "5.2.0" }, { "fixed": "6.18.33" } ], "type": "ECOSYSTEM" }, { "events": [ { "introduced": "6.19.0" }, { "fixed": "7.0.10" } ], "type": "ECOSYSTEM" } ] } ], "database_specific": { "cna_assigner": "Linux", "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/52xxx/CVE-2026-52991.json" }, "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nsched/psi: fix race between file release and pressure write\n\nA potential race condition exists between pressure write and cgroup file\nrelease regarding the priv member of struct kernfs_open_file, which\ntriggers the uaf reported in [1].\n\nConsider the following scenario involving execution on two separate CPUs:\n\n CPU0\t\t\t\t\tCPU1\n ====\t\t\t\t\t====\n\t\t\t\t\tvfs_rmdir()\n\t\t\t\t\tkernfs_iop_rmdir()\n\t\t\t\t\tcgroup_rmdir()\n\t\t\t\t\tcgroup_kn_lock_live()\n\t\t\t\t\tcgroup_destroy_locked()\n\t\t\t\t\tcgroup_addrm_files()\n\t\t\t\t\tcgroup_rm_file()\n\t\t\t\t\tkernfs_remove_by_name()\n\t\t\t\t\tkernfs_remove_by_name_ns()\n vfs_write()\t\t\t\t__kernfs_remove()\n new_sync_write()\t\t\tkernfs_drain()\n kernfs_fop_write_iter()\t\tkernfs_drain_open_files()\n cgroup_file_write()\t\t\tkernfs_release_file()\n pressure_write()\t\t\tcgroup_file_release()\n ctx = of-\u003epriv;\n\t\t\t\t\tkfree(ctx);\n \t\t\t\t\tof-\u003epriv = NULL;\n\t\t\t\t\tcgroup_kn_unlock()\n cgroup_kn_lock_live()\n cgroup_get(cgrp)\n cgroup_kn_unlock()\n if (ctx-\u003epsi.trigger) // here, trigger uaf for ctx, that is of-\u003epriv\n\nThe cgroup_rmdir() is protected by the cgroup_mutex, it also safeguards\nthe memory deallocation of of-\u003epriv performed within cgroup_file_release().\nHowever, the operations involving of-\u003epriv executed within pressure_write()\nare not entirely covered by the protection of cgroup_mutex. Consequently,\nif the code in pressure_write(), specifically the section handling the\nctx variable executes after cgroup_file_release() has completed, a uaf\nvulnerability involving of-\u003epriv is triggered.\n\nTherefore, the issue can be resolved by extending the scope of the\ncgroup_mutex lock within pressure_write() to encompass all code paths\ninvolving of-\u003epriv, thereby properly synchronizing the race condition\noccurring between cgroup_file_release() and pressure_write().\n\nAnd, if an live kn lock can be successfully acquired while executing\nthe pressure write operation, it indicates that the cgroup deletion\nprocess has not yet reached its final stage; consequently, the priv\npointer within open_file cannot be NULL. Therefore, the operation to\nretrieve the ctx value must be moved to a point *after* the live kn\nlock has been successfully acquired.\n\nIn another situation, specifically after entering cgroup_kn_lock_live()\nbut before acquiring cgroup_mutex, there exists a different class of\nrace condition:\n\nCPU0: write memory.pressure CPU1: write cgroup.pressure=0\n===========================\t\t =============================\n\nkernfs_fop_write_iter()\n kernfs_get_active_of(of)\n pressure_write()\n cgroup_kn_lock_live(memory.pressure)\n cgroup_tryget(cgrp)\n kernfs_break_active_protection(kn)\n ... blocks on cgroup_mutex\n\n \t cgroup_pressure_write()\n \t cgroup_kn_lock_live(cgroup.pressure)\n \t cgroup_file_show(memory.pressure, false)\n \t kernfs_show(false)\n \t kernfs_drain_open_files()\n \t cgroup_file_release(of)\n \t kfree(ctx)\n \t of-\u003epriv = NULL\n \t cgroup_kn_unlock()\n\n ... acquires cgroup_mutex\n ctx = of-\u003epriv; // may now be NULL\n if (ctx-\u003epsi.trigger) // NULL dereference\n\nConsequently, there is a possibility that of-\u003epriv is NULL, the pressure\nwrite needs to check for this.\n\nNow that the scope of the cgroup_mutex has been expanded, the original\nexplicit cgroup_get/put operations are no longer necessary, this is\nbecause acquiring/releasing the live kn lock inherently executes a\ncgroup get/put operation.\n\n[1]\nBUG: KASAN: slab-use-after-free in pressure_write+0xa4/0x210 kernel/cgroup/cgroup.c:4011\nCall Trace:\n pressure_write+0xa4/0x210 kernel/cgroup/cgroup.c:4011\n cgroup_file_write+0x36f/0x790 kernel/cgroup/cgroup.c:43\n---truncated---", "id": "CVE-2026-52991", "modified": "2026-07-08T05:39:04.382972239Z", "published": "2026-06-24T16:29:04.810Z", "references": [ { "type": "WEB", "url": "https://git.kernel.org/stable/c/03dc070fa0fc3cb4068693f468ccd5f8a7e58282" }, { "type": "WEB", "url": "https://git.kernel.org/stable/c/a5b98009f16d8a5fb4a8ff9a193f5735515c38fa" }, { "type": "WEB", "url": "https://git.kernel.org/stable/c/d4352c0709bfd38c752fccbde7fd72a82ac78f23" }, { "type": "WEB", "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-52991.json" }, { "type": "ADVISORY", "url": "https://access.redhat.com/security/cve/CVE-2026-52991" }, { "type": "ADVISORY", "url": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/52xxx/CVE-2026-52991.json" }, { "type": "ADVISORY", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-52991" }, { "type": "REPORT", "url": "https://bugzilla.redhat.com/show_bug.cgi?id=2492403" }, { "type": "PACKAGE", "url": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git" } ], "schema_version": "1.7.5", "severity": [ { "score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H", "type": "CVSS_V3" } ], "summary": "sched/psi: fix race between file release and pressure write" }