{"id":"CVE-2025-39977","summary":"futex: Prevent use-after-free during requeue-PI","details":"In the Linux kernel, the following vulnerability has been resolved:\n\nfutex: Prevent use-after-free during requeue-PI\n\nsyzbot managed to trigger the following race:\n\n   T1                               T2\n\n futex_wait_requeue_pi()\n   futex_do_wait()\n     schedule()\n                               futex_requeue()\n                                 futex_proxy_trylock_atomic()\n                                   futex_requeue_pi_prepare()\n                                   requeue_pi_wake_futex()\n                                     futex_requeue_pi_complete()\n                                      /* preempt */\n\n         * timeout/ signal wakes T1 *\n\n   futex_requeue_pi_wakeup_sync() // Q_REQUEUE_PI_LOCKED\n   futex_hash_put()\n  // back to userland, on stack futex_q is garbage\n\n                                      /* back */\n                                     wake_up_state(q-\u003etask, TASK_NORMAL);\n\nIn this scenario futex_wait_requeue_pi() is able to leave without using\nfutex_q::lock_ptr for synchronization.\n\nThis can be prevented by reading futex_q::task before updating the\nfutex_q::requeue_state. A reference on the task_struct is not needed\nbecause requeue_pi_wake_futex() is invoked with a spinlock_t held which\nimplies a RCU read section.\n\nEven if T1 terminates immediately after, the task_struct will remain valid\nduring T2's wake_up_state().  A READ_ONCE on futex_q::task before\nfutex_requeue_pi_complete() is enough because it ensures that the variable\nis read before the state is updated.\n\nRead futex_q::task before updating the requeue state, use it for the\nfollowing wakeup.","modified":"2026-04-16T04:31:08.231359062Z","published":"2025-10-15T07:55:58.283Z","related":["SUSE-SU-2026:0263-1","SUSE-SU-2026:0278-1","SUSE-SU-2026:0281-1","SUSE-SU-2026:0293-1","SUSE-SU-2026:0315-1","SUSE-SU-2026:0317-1","SUSE-SU-2026:0411-1","SUSE-SU-2026:0617-1","SUSE-SU-2026:20207-1","SUSE-SU-2026:20220-1","SUSE-SU-2026:20228-1","SUSE-SU-2026:20477-1","SUSE-SU-2026:20498-1","SUSE-SU-2026:20845-1","SUSE-SU-2026:20876-1","openSUSE-SU-2026:20145-1"],"database_specific":{"osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2025/39xxx/CVE-2025-39977.json","cna_assigner":"Linux"},"references":[{"type":"WEB","url":"https://git.kernel.org/stable/c/348736955ed6ca6e99ca24b93b1d3fbfe352c181"},{"type":"WEB","url":"https://git.kernel.org/stable/c/a170b9c0dde83312b8b58ccc91509c7c15711641"},{"type":"WEB","url":"https://git.kernel.org/stable/c/b549113738e8c751b613118032a724b772aa83f2"},{"type":"WEB","url":"https://git.kernel.org/stable/c/cb5d19a61274b51b49601214a87af573b43d60fa"},{"type":"WEB","url":"https://git.kernel.org/stable/c/d824b2dbdcfe3c390278dd9652ea526168ef6850"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2025/39xxx/CVE-2025-39977.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2025-39977"},{"type":"PACKAGE","url":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","events":[{"introduced":"07d91ef510fb16a2e0ca7453222105835b7ba3b8"},{"fixed":"cb5d19a61274b51b49601214a87af573b43d60fa"},{"fixed":"348736955ed6ca6e99ca24b93b1d3fbfe352c181"},{"fixed":"a170b9c0dde83312b8b58ccc91509c7c15711641"},{"fixed":"d824b2dbdcfe3c390278dd9652ea526168ef6850"},{"fixed":"b549113738e8c751b613118032a724b772aa83f2"}]}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2025-39977.json"}},{"package":{"name":"Kernel","ecosystem":"Linux"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"5.15.0"},{"fixed":"6.1.155"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.2.0"},{"fixed":"6.6.109"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.7.0"},{"fixed":"6.12.50"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.13.0"},{"fixed":"6.16.10"}]}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2025-39977.json"}}],"schema_version":"1.7.5"}