fs/resctrl: Prevent use-after-free in rdtgroup_kn_put()

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Summary

CVECVE-2026-93100
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-09-17 17:18:04 UTC
Updated2026-09-17 17:18:04 UTC
DescriptionIn the Linux kernel, the following vulnerability has been resolved: fs/resctrl: Prevent use-after-free in rdtgroup_kn_put() A struct rdtgroup is reference counted via rdtgroup::waitcount. Callers that need the structure to remain valid across a sleep (while waiting on acquiring rdtgroup_mutex) take a reference with rdtgroup_kn_get() and release it with rdtgroup_kn_put(). The release path is intended to serve as the fallback freer: if the count drops to zero and the group has already been marked RDT_DELETED, rdtgroup_kn_put() frees the structure. The bulk teardown paths free_all_child_rdtgrp() and rmdir_all_sub() resulting from a resctrl directory remove or resctrl fs unmount act as the primary freer: they hold rdtgroup_mutex and free each rdtgroup whose waitcount is zero, otherwise they set RDT_DELETED and leave the freeing to the last waiter. These two freers race. rdtgroup_kn_put() commits waitcount == 0 with atomic_dec_and_test() outside rdtgroup_mutex, then reads rdtgroup::flags. Between those two operations a concurrent caller of free_all_child_rdtgrp() or rmdir_all_sub() (which holds the mutex) can observe waitcount == 0 via atomic_read(), call rdtgroup_remove(), and kfree() the structure. The subsequent read of rdtgroup::flags in rdtgroup_kn_put() is then a use-after-free, and the structure may even be freed twice if the freed memory happens to satisfy the RDT_DELETED flag check. Replace the bare atomic_dec_and_test() with atomic_dec_and_mutex_lock() so that the decrement-to-zero takes rdtgroup_mutex before the count becomes globally visible. The inspection of rdtgroup::flags then runs under the same mutex held by the bulk freers, making the two paths mutually exclusive. The common case where the count does not reach zero remains lock-free. Defer kernfs_unbreak_active_protection() until after the mutex is dropped since kernfs active protections functionally wrap rdtgroup_mutex. Remove resource group, which in turn drops its kernfs reference, after kernfs protection is restored. [ bp: Split the commit messsages into smaller, easier-parseable paragraphs. ]

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected b8511ccc75c033f6d54188ea4df7bf1e85778740 ae69f936e8ffed553d899ba4c02f8a7461a89e54 git Not specified
CNA Linux Linux affected b8511ccc75c033f6d54188ea4df7bf1e85778740 4c593c62c1499665baebbb41b70e2c9b7e947b86 git Not specified
CNA Linux Linux affected b8511ccc75c033f6d54188ea4df7bf1e85778740 f5bcf539484d2d604c2f2330e09487ea090b21c7 git Not specified
CNA Linux Linux affected d20edc0bca5577bab38acb5b190619c922ddebf8 git Not specified
CNA Linux Linux affected 1b006f8cbde9f3dabdfafe2ff7aa9f831ed5b625 git Not specified
CNA Linux Linux affected 40300f986e47dbc8f1d02e5080385f5cf9f85f70 git Not specified
CNA Linux Linux affected b5a4949897ebada8132d54c93208989482503103 git Not specified
CNA Linux Linux affected 4.14.170 4.15 semver Not specified
CNA Linux Linux affected 4.19.102 4.20 semver Not specified
CNA Linux Linux affected 5.4.18 5.5 semver Not specified
CNA Linux Linux affected 5.5.2 5.6 semver Not specified
CNA Linux Linux affected 5.6 Not specified
CNA Linux Linux unaffected 5.6 semver Not specified
CNA Linux Linux unaffected 6.18.52 6.18.* semver Not specified
CNA Linux Linux unaffected 7.2.6 7.2.* semver Not specified
CNA Linux Linux unaffected 7.3-rc1 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/4c593c62c1499665baebbb41b70e2c9b7e947b86 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/f5bcf539484d2d604c2f2330e09487ea090b21c7 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/ae69f936e8ffed553d899ba4c02f8a7461a89e54 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
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