{"id":"CVE-2026-93100","title":"In the Linux kernel, the following vulnerability has been resolved:\n\nfs/resctrl: Prevent use-after-free in rdtgroup_kn_put()\n\nA struct rdtgroup is reference counted via rdtgroup::waitcount","summary":"In the Linux kernel, the following vulnerability has been resolved:\n\nfs/resctrl: Prevent use-after-free in rdtgroup_kn_put()\n\nA struct rdtgroup is reference counted via rdtgroup::waitcount. Callers that\nneed the structure to remain valid…","severity":"none","vendor":"Linux","product":"Linux","affected":["Linux >= b8511ccc75c033f6d54188ea4df7bf1e85778740 < ae69f936e8ffed553d899ba4c02f8a7461a89e54","Linux >= b8511ccc75c033f6d54188ea4df7bf1e85778740 < 4c593c62c1499665baebbb41b70e2c9b7e947b86","Linux >= b8511ccc75c033f6d54188ea4df7bf1e85778740 < f5bcf539484d2d604c2f2330e09487ea090b21c7","Linux d20edc0bca5577bab38acb5b190619c922ddebf8","Linux 1b006f8cbde9f3dabdfafe2ff7aa9f831ed5b625","Linux 40300f986e47dbc8f1d02e5080385f5cf9f85f70","Linux b5a4949897ebada8132d54c93208989482503103","Linux >= 4.14.170 < 4.15","Linux >= 4.19.102 < 4.20","Linux >= 5.4.18 < 5.5","Linux >= 5.5.2 < 5.6","Linux 5.6"],"published":"2026-09-17","updated":"2026-09-17","sourceUpdated":"2026-09-17T17:18:04.223","source":"NVD","sourceUrl":"https://nvd.nist.gov/vuln/detail/CVE-2026-93100","references":[{"url":"https://git.kernel.org/stable/c/4c593c62c1499665baebbb41b70e2c9b7e947b86","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/ae69f936e8ffed553d899ba4c02f8a7461a89e54","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/f5bcf539484d2d604c2f2330e09487ea090b21c7","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"}],"tags":["nvd","cve.org"],"ingestedAt":"2026-09-17T16:21:47.757Z","epss":0.00166,"epssPercentile":0.06255,"slug":"CVE-2026-93100","body":"## Overview\n\nIn the Linux kernel, the following vulnerability has been resolved:\n\nfs/resctrl: Prevent use-after-free in rdtgroup_kn_put()\n\nA struct rdtgroup is reference counted via rdtgroup::waitcount. Callers that\nneed the structure to remain valid across a sleep (while waiting on acquiring\nrdtgroup_mutex) take a reference with rdtgroup_kn_get() and release it with\nrdtgroup_kn_put().\n\nThe release path is intended to serve as the fallback freer: if the count\ndrops to zero and the group has already been marked RDT_DELETED,\nrdtgroup_kn_put() frees the structure.\n\nThe bulk teardown paths free_all_child_rdtgrp() and rmdir_all_sub() resulting\nfrom a resctrl directory remove or resctrl fs unmount act as the primary\nfreer: they hold rdtgroup_mutex and free each rdtgroup whose waitcount is\nzero, otherwise they set RDT_DELETED and leave the freeing to the last waiter.\n\nThese two freers race. rdtgroup_kn_put() commits waitcount == 0 with\natomic_dec_and_test() outside rdtgroup_mutex, then reads rdtgroup::flags.\nBetween those two operations a concurrent caller of free_all_child_rdtgrp()\nor rmdir_all_sub() (which holds the mutex) can observe waitcount == 0 via\natomic_read(), call rdtgroup_remove(), and kfree() the structure.\n\nThe subsequent read of rdtgroup::flags in rdtgroup_kn_put() is then\na use-after-free, and the structure may even be freed twice if the freed\nmemory happens to satisfy the RDT_DELETED flag check.\n\nReplace the bare atomic_dec_and_test() with atomic_dec_and_mutex_lock() so\nthat the decrement-to-zero takes rdtgroup_mutex before the count becomes\nglobally visible. The inspection of rdtgroup::flags then runs under the same\nmutex held by the bulk freers, making the two paths mutually exclusive.\n\nThe common case where the count does not reach zero remains lock-free. Defer\nkernfs_unbreak_active_protection() until after the mutex is dropped since\nkernfs active protections functionally wrap rdtgroup_mutex. Remove resource\ngroup, which in turn drops its kernfs reference, after kernfs protection is\nrestored.\n\n  [ bp: Split the commit messsages into smaller, easier-parseable paragraphs. ]\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.","depth":"sunlit","depthScore":3,"depthScoreParts":{"impact":2.8,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[]}