{"id":"CVE-2026-93100","state":"PUBLISHED","title":"fs/resctrl: Prevent use-after-free in rdtgroup_kn_put()","description":"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 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. ]","publishedAt":"2026-09-17T16:11:13.077Z","updatedAt":"2026-10-30T12:35:58.210Z","severity":null,"assigner":"Linux","products":["Linux Linux"],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"b8511ccc75c033f6d54188ea4df7bf1e85778740","status":"affected","lessThan":"906b3044dbf7c38cc411f7cf457c811363161e3b","versionType":"git"},{"version":"b8511ccc75c033f6d54188ea4df7bf1e85778740","status":"affected","lessThan":"971b40e3ca1279ca4917889e0195d33b66d071a4","versionType":"git"},{"version":"b8511ccc75c033f6d54188ea4df7bf1e85778740","status":"affected","lessThan":"828ff461c136b95d13b8d712c0a7a06a640e313a","versionType":"git"},{"version":"b8511ccc75c033f6d54188ea4df7bf1e85778740","status":"affected","lessThan":"ae69f936e8ffed553d899ba4c02f8a7461a89e54","versionType":"git"},{"version":"b8511ccc75c033f6d54188ea4df7bf1e85778740","status":"affected","lessThan":"4c593c62c1499665baebbb41b70e2c9b7e947b86","versionType":"git"},{"version":"b8511ccc75c033f6d54188ea4df7bf1e85778740","status":"affected","lessThan":"f5bcf539484d2d604c2f2330e09487ea090b21c7","versionType":"git"},{"version":"d20edc0bca5577bab38acb5b190619c922ddebf8","status":"affected","versionType":"git"},{"version":"1b006f8cbde9f3dabdfafe2ff7aa9f831ed5b625","status":"affected","versionType":"git"},{"version":"40300f986e47dbc8f1d02e5080385f5cf9f85f70","status":"affected","versionType":"git"},{"version":"b5a4949897ebada8132d54c93208989482503103","status":"affected","versionType":"git"},{"version":"4.14.170","status":"affected","lessThan":"4.15","versionType":"semver"},{"version":"4.19.102","status":"affected","lessThan":"4.20","versionType":"semver"},{"version":"5.4.18","status":"affected","lessThan":"5.5","versionType":"semver"},{"version":"5.5.2","status":"affected","lessThan":"5.6","versionType":"semver"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/resctrl/rdtgroup.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"5.6","status":"affected"},{"version":"0","status":"unaffected","lessThan":"5.6","versionType":"semver"},{"version":"6.1.191","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.160","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.114","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.52","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.2.6","status":"unaffected","lessThanOrEqual":"7.2.*","versionType":"semver"},{"version":"7.3","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/resctrl/rdtgroup.c"]}],"references":["https://git.kernel.org/stable/c/906b3044dbf7c38cc411f7cf457c811363161e3b","https://git.kernel.org/stable/c/971b40e3ca1279ca4917889e0195d33b66d071a4","https://git.kernel.org/stable/c/828ff461c136b95d13b8d712c0a7a06a640e313a","https://git.kernel.org/stable/c/ae69f936e8ffed553d899ba4c02f8a7461a89e54","https://git.kernel.org/stable/c/4c593c62c1499665baebbb41b70e2c9b7e947b86","https://git.kernel.org/stable/c/f5bcf539484d2d604c2f2330e09487ea090b21c7"],"weaknesses":[],"ingestedAt":"2026-10-30T12:54:04.478Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/93xxx/CVE-2026-93100.json","commit":"1f312381e38164a43607eebab851b151dd16861e","baselineCommit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-93100","state":"PUBLISHED","datePublished":"2026-09-17T16:11:13.077Z","dateUpdated":"2026-10-30T12:35:58.210Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2026-09-17T16:02:15.085Z"},"containers":{"cna":{"title":"fs/resctrl: Prevent use-after-free in rdtgroup_kn_put()","descriptions":[{"lang":"en","value":"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 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. ]"}],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"b8511ccc75c033f6d54188ea4df7bf1e85778740","status":"affected","lessThan":"906b3044dbf7c38cc411f7cf457c811363161e3b","versionType":"git"},{"version":"b8511ccc75c033f6d54188ea4df7bf1e85778740","status":"affected","lessThan":"971b40e3ca1279ca4917889e0195d33b66d071a4","versionType":"git"},{"version":"b8511ccc75c033f6d54188ea4df7bf1e85778740","status":"affected","lessThan":"828ff461c136b95d13b8d712c0a7a06a640e313a","versionType":"git"},{"version":"b8511ccc75c033f6d54188ea4df7bf1e85778740","status":"affected","lessThan":"ae69f936e8ffed553d899ba4c02f8a7461a89e54","versionType":"git"},{"version":"b8511ccc75c033f6d54188ea4df7bf1e85778740","status":"affected","lessThan":"4c593c62c1499665baebbb41b70e2c9b7e947b86","versionType":"git"},{"version":"b8511ccc75c033f6d54188ea4df7bf1e85778740","status":"affected","lessThan":"f5bcf539484d2d604c2f2330e09487ea090b21c7","versionType":"git"},{"version":"d20edc0bca5577bab38acb5b190619c922ddebf8","status":"affected","versionType":"git"},{"version":"1b006f8cbde9f3dabdfafe2ff7aa9f831ed5b625","status":"affected","versionType":"git"},{"version":"40300f986e47dbc8f1d02e5080385f5cf9f85f70","status":"affected","versionType":"git"},{"version":"b5a4949897ebada8132d54c93208989482503103","status":"affected","versionType":"git"},{"version":"4.14.170","status":"affected","lessThan":"4.15","versionType":"semver"},{"version":"4.19.102","status":"affected","lessThan":"4.20","versionType":"semver"},{"version":"5.4.18","status":"affected","lessThan":"5.5","versionType":"semver"},{"version":"5.5.2","status":"affected","lessThan":"5.6","versionType":"semver"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/resctrl/rdtgroup.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"5.6","status":"affected"},{"version":"0","status":"unaffected","lessThan":"5.6","versionType":"semver"},{"version":"6.1.191","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.160","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.114","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.52","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.2.6","status":"unaffected","lessThanOrEqual":"7.2.*","versionType":"semver"},{"version":"7.3","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/resctrl/rdtgroup.c"]}],"references":[{"url":"https://git.kernel.org/stable/c/906b3044dbf7c38cc411f7cf457c811363161e3b"},{"url":"https://git.kernel.org/stable/c/971b40e3ca1279ca4917889e0195d33b66d071a4"},{"url":"https://git.kernel.org/stable/c/828ff461c136b95d13b8d712c0a7a06a640e313a"},{"url":"https://git.kernel.org/stable/c/ae69f936e8ffed553d899ba4c02f8a7461a89e54"},{"url":"https://git.kernel.org/stable/c/4c593c62c1499665baebbb41b70e2c9b7e947b86"},{"url":"https://git.kernel.org/stable/c/f5bcf539484d2d604c2f2330e09487ea090b21c7"}],"providerMetadata":{"shortName":"Linux","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateUpdated":"2026-10-30T12:35:58.210Z"},"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.6","versionEndExcluding":"6.1.191"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.6","versionEndExcluding":"6.6.160"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.6","versionEndExcluding":"6.12.114"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.6","versionEndExcluding":"6.18.52"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.6","versionEndExcluding":"7.2.6"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.6","versionEndExcluding":"7.3"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.14.170"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.19.102"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.4.18"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.5.2"}]}]}],"x_generator":{"engine":"bippy-1.2.0"}}}}}