{"id":"CVE-2026-89689","summary":"nfsd: don't free session slots that are still in use","details":"In the Linux kernel, the following vulnerability has been resolved:\n\nnfsd: don't free session slots that are still in use\n\nnfsd4_sequence() can free the very slot it is currently processing.\nWhen the session shrinker has reduced se_target_maxslots below\nse_fchannel.maxreqs, the shrink path checks three conditions before\ncalling free_session_slots():\n\n  1. se_target_maxslots \u003c maxreqs  (shrink was advertised)\n  2. slot-\u003esl_generation == se_slot_gen  (slot is up-to-date)\n  3. seq-\u003emaxslots \u003c= se_target_maxslots  (client acknowledges)\n\nHowever, seq-\u003eslotid is never checked against se_target_maxslots.\nA client using a slot in the range [se_target_maxslots, maxreqs) can\nsatisfy all three conditions: its slot has the current generation\n(set by a prior SEQUENCE), and it sends sa_highest_slotid \u003c=\nse_target_maxslots to acknowledge the reduction.\n\nfree_session_slots() then kfrees every slot at index \u003e=\nse_target_maxslots, including the caller's own slot. The function\ncontinues to write sl_seqid, sl_flags, sl_generation, and stores the\ndangling pointer in cstate-\u003eslot. Later, nfsd4_store_cache_entry()\ncopies up to maxresp_cached bytes of the compound reply into the freed\nsl_data[] array, corrupting whatever slab object now occupies that\naddress.\n\nAdditionally, a concurrent thread processing SEQUENCE on a different\nhigh-numbered slot can have its slot freed out from under it.\nNFSD4_SLOT_INUSE is set under nn-\u003eclient_lock before the lock is\nreleased, so any concurrent thread past SEQUENCE will have its slot\nmarked. However, free_session_slots() does not check NFSD4_SLOT_INUSE\nbefore freeing.\n\nFix both problems by:\n 1. Checking that the current request's slotid is below the shrink\n    boundary.\n 2. Scanning slots in the to-be-freed range for NFSD4_SLOT_INUSE and\n    deferring the shrink if any are active.","modified":"2026-09-14T03:46:25.379809836Z","published":"2026-09-11T19:46:09.976Z","database_specific":{"cna_assigner":"Linux","osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/89xxx/CVE-2026-89689.json"},"references":[{"type":"WEB","url":"https://git.kernel.org/stable/c/72d40b103bb03f0124d3a3c8f71a30cbafaf6afa"},{"type":"WEB","url":"https://git.kernel.org/stable/c/b449b134e7762ddf98653a4b1d3e76d2d212ea64"},{"type":"WEB","url":"https://git.kernel.org/stable/c/f5d22e372f4ac3eb287037a488c29691d52a6330"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/89xxx/CVE-2026-89689.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-89689"},{"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":"fc8738c68d0bbf5033dd98b4f63d277ecbd49fd7"},{"fixed":"72d40b103bb03f0124d3a3c8f71a30cbafaf6afa"},{"fixed":"b449b134e7762ddf98653a4b1d3e76d2d212ea64"},{"fixed":"f5d22e372f4ac3eb287037a488c29691d52a6330"}]}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-89689.json"}},{"package":{"name":"Kernel","ecosystem":"Linux"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"6.14.0"},{"fixed":"6.18.50"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.19.0"},{"fixed":"7.2.4"}]}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-89689.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H"}]}