{"id":"CVE-2026-80527","title":"ceph: fix hanging __ceph_get_caps() with stale mds_wanted","summary":"In the Linux kernel, the following vulnerability has been resolved:\n\nceph: fix hanging __ceph_get_caps() with stale mds_wanted\n\nA reader can hang forever in __ceph_get_caps() when the client no\nlonger holds `FILE_RD`, but local cap state…","severity":"high","cvss":7.5,"cvssVector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","cvssSource":"cna","vendor":"Linux","product":"Linux","affected":["Linux >= 0a454bdd501ad1aa30bb72e9581efa338ad6ce5c < b5661524c5a45085a866864ca9b8ae2513dfd67a","Linux >= 0a454bdd501ad1aa30bb72e9581efa338ad6ce5c < 5e84bc6f67e19fdd192d8b215de728acbfc12572","Linux >= 0a454bdd501ad1aa30bb72e9581efa338ad6ce5c < 5fedf279a1ea369d39c8b06dd4547cdc576065d0","Linux >= 0a454bdd501ad1aa30bb72e9581efa338ad6ce5c < e05c315b4da0c16ea800ee4b2cb6c617f586d1b5","Linux >= 0a454bdd501ad1aa30bb72e9581efa338ad6ce5c < fcce1b3be6d286aa80831e730289f4c062053ae6","Linux >= 0a454bdd501ad1aa30bb72e9581efa338ad6ce5c < a3bc6b3e9ef3f5f5cb85a902a30a090c7931127c","Linux >= 0a454bdd501ad1aa30bb72e9581efa338ad6ce5c < 9e55fe24c548ad3163903eb58bb002d28d32a630","Linux >= 0a454bdd501ad1aa30bb72e9581efa338ad6ce5c < 50958bb928bad3bdba9e5d1b7ff4bbadcf6951e6","Linux 5.8"],"ssvc":{"exploitation":"none","automatable":"yes","technicalImpact":"partial","timestamp":"2026-10-16T19:16:34.310764Z"},"published":"2026-08-26","updated":"2026-10-16","sourceUpdated":"2026-10-16T19:26:24.678Z","source":"CVEORG","sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-80527","references":[{"url":"https://git.kernel.org/stable/c/b5661524c5a45085a866864ca9b8ae2513dfd67a"},{"url":"https://git.kernel.org/stable/c/5e84bc6f67e19fdd192d8b215de728acbfc12572"},{"url":"https://git.kernel.org/stable/c/5fedf279a1ea369d39c8b06dd4547cdc576065d0"},{"url":"https://git.kernel.org/stable/c/e05c315b4da0c16ea800ee4b2cb6c617f586d1b5"},{"url":"https://git.kernel.org/stable/c/fcce1b3be6d286aa80831e730289f4c062053ae6"},{"url":"https://git.kernel.org/stable/c/a3bc6b3e9ef3f5f5cb85a902a30a090c7931127c"},{"url":"https://git.kernel.org/stable/c/9e55fe24c548ad3163903eb58bb002d28d32a630"},{"url":"https://git.kernel.org/stable/c/50958bb928bad3bdba9e5d1b7ff4bbadcf6951e6"}],"tags":["cve.org"],"epss":0.00501,"epssPercentile":0.4155,"ingestedAt":"2026-10-16T19:46:24.321Z","slug":"CVE-2026-80527","body":"## Overview\n\nIn the Linux kernel, the following vulnerability has been resolved:\n\nceph: fix hanging __ceph_get_caps() with stale mds_wanted\n\nA reader can hang forever in __ceph_get_caps() when the client no\nlonger holds `FILE_RD`, but local cap state still says that the\ncapability is already wanted (via `mds_wanted`).\n\nOne way to trigger this is through MDS cap revocation.  If another\nclient performs a conflicting operation, the MDS can revoke `FILE_RD`\nfrom the reader; the next read then has to reacquire `FILE_RD`.  If\nthe cap update that should request `FILE_RD` never reaches the MDS\nafter `cap->mds_wanted` was raised, the reader is left holding only\nnon-file caps while local `mds_wanted` still includes the file read\ncaps.\n\nIn that state, try_get_cap_refs() sees `need <= mds_wanted` and\nreturns 0, so __ceph_get_caps() just waits on `i_cap_wq`.  If the cap\nupdate that was supposed to request `FILE_RD never reaches the MDS\nafter `cap->mds_wanted was` raised, no further request is sent and the\nwaiter can sleep indefinitely until unrelated cap traffic happens to\nwake it up.\n\nThe ordering issue is that `cap->mds_wanted` is updated in\n__prep_cap() before the `CEPH_MSG_CLIENT_CAPS message` is actually\nqueued for send.  That makes one field serve two different meanings at\nonce: what this client wants, and what the client believes the MDS\nalready knows it wants.\n\nA proper fix would be to split those states and track whether a cap\nupdate is actually in flight or has been observed by the MDS.\nHowever, simply moving the `cap->mds_wanted assignment` later would\nnot be sufficient: queueing the message in the messenger does not\nguarantee that the MDS processed that specific wanted set, and\nreconnect or message loss can still invalidate that assumption.\nFixing that properly would require a larger rework of the cap state\nmachine.\n\nTo allow simpler backports to stable kernels, this patch implements a\nsimpler workaround:\n\n- stop waiting forever in __ceph_get_caps(); after a bounded wait,\n  fall back to the renew path\n\n- make ceph_renew_caps() issue a synchronous `OPEN` request whenever\n  the inode still does not actually hold the wanted caps, instead of\n  only calling ceph_check_caps()\n\nThe extra issued-vs-wanted check in ceph_renew_caps() is necessary\nbecause the previous test only checked whether the inode still had any\nreal caps at all.  That is not enough after revocation: the client can\nstill hold something like `pLs` and yet be missing `FILE_RD`\ncompletely.  In that case, falling back to ceph_check_caps() is not\nsufficient, because it still trusts `cap->mds_wanted` and may resend\nnothing.  By requiring `(issued & wanted) == wanted` before taking the\nasynchronous path, the code only uses ceph_check_caps() when the\n`wanted caps` are already actually issued.  Otherwise, it sends the\nsynchronous `OPEN` renew.\n\nThis preserves the existing asynchronous fast path when the wanted\ncaps are already issued, avoids changing cap-state semantics, and\nfixes the hang by guaranteeing that a stalled waiter eventually\nretries through a path that does not rely on the stale `mds_wanted`\nstate.\n\n[ idryomov: move CEPH_GET_CAPS_WAIT_TIMEOUT from libceph.h to\n  mds_client.h, formatting ]\n\n## Affected\n\n- `Linux >= 0a454bdd501ad1aa30bb72e9581efa338ad6ce5c < b5661524c5a45085a866864ca9b8ae2513dfd67a`\n- `Linux >= 0a454bdd501ad1aa30bb72e9581efa338ad6ce5c < 5e84bc6f67e19fdd192d8b215de728acbfc12572`\n- `Linux >= 0a454bdd501ad1aa30bb72e9581efa338ad6ce5c < 5fedf279a1ea369d39c8b06dd4547cdc576065d0`\n- `Linux >= 0a454bdd501ad1aa30bb72e9581efa338ad6ce5c < e05c315b4da0c16ea800ee4b2cb6c617f586d1b5`\n- `Linux >= 0a454bdd501ad1aa30bb72e9581efa338ad6ce5c < fcce1b3be6d286aa80831e730289f4c062053ae6`\n- `Linux >= 0a454bdd501ad1aa30bb72e9581efa338ad6ce5c < a3bc6b3e9ef3f5f5cb85a902a30a090c7931127c`\n- `Linux >= 0a454bdd501ad1aa30bb72e9581efa338ad6ce5c < 9e55fe24c548ad3163903eb58bb002d28d32a630`\n- `Linux >= 0a454bdd501ad1aa30bb72e9581efa338ad6ce5c < 50958bb928bad3bdba9e5d1b7ff4bbadcf6951e6`\n- `Linux 5.8`\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.","depth":"twilight","depthScore":41,"depthScoreParts":{"impact":41.3,"likelihood":0.1,"exploitation":0,"ransomware":0},"changes":[]}