CVE-2026-52991: Software Security Vulnerability Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-3v2r-c9x3-5fgr",
  "modified" : "2026-08-20T15:33:25Z",
  "published" : "2026-06-24T18:32:42Z",
  "aliases" : [ "CVE-2026-52991" ],
  "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->priv;\n\t\t\t\t\tkfree(ctx);\n \t\t\t\t\tof->priv = 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->psi.trigger)  // here, trigger uaf for ctx, that is of->priv\n\nThe cgroup_rmdir() is protected by the cgroup_mutex, it also safeguards\nthe memory deallocation of of->priv performed within cgroup_file_release().\nHowever, the operations involving of->priv 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->priv 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->priv, 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->priv = NULL\n                                     \t  cgroup_kn_unlock()\n\n   ... acquires cgroup_mutex\n   ctx = of->priv;        // may now be NULL\n   if (ctx->psi.trigger)  // NULL dereference\n\nConsequently, there is a possibility that of->priv 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---",
  "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-2026-52991"
  }, {
    "type" : "WEB",
    "url" : "https://access.redhat.com/errata/RHSA-2026:57251"
  }, {
    "type" : "WEB",
    "url" : "https://access.redhat.com/errata/RHSA-2026:57252"
  }, {
    "type" : "WEB",
    "url" : "https://access.redhat.com/errata/RHSA-2026:57253"
  }, {
    "type" : "WEB",
    "url" : "https://access.redhat.com/errata/RHSA-2026:57254"
  }, {
    "type" : "WEB",
    "url" : "https://access.redhat.com/security/cve/CVE-2026-52991"
  }, {
    "type" : "WEB",
    "url" : "https://bugzilla.redhat.com/show_bug.cgi?id=2492403"
  }, {
    "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"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-362", "CWE-367" ],
    "severity" : "HIGH",
    "github_reviewed" : false,
    "github_reviewed_at" : null,
    "nvd_published_at" : "2026-06-24T17:17:09Z"
  }
}