{"id":"CVE-2026-99016","summary":"riscv: futex: untag the user pointer before the atomic access","details":"In the Linux kernel, the following vulnerability has been resolved:\n\nriscv: futex: untag the user pointer before the atomic access\n\naccess_ok() checks untagged_addr(uaddr), but arch_futex_atomic_op_inuser()\nand futex_atomic_cmpxchg_inatomic() hand the raw uaddr to the inline asm\namoswap/amoadd/.../lr.w+sc.w through the \"+m\" (*uaddr) operand.  When the\ntagged address ABI is enabled (CONFIG_RISCV_ISA_SUPM, prctl\nPR_SET_TAGGED_ADDR_CTRL with PMLEN != 0), those two addresses differ: a\nuser pointer whose top PMLEN bits hold a tag passes access_ok() after\nuntagging, but the atomic is then performed on the still-tagged raw\naddress.\n\nSupervisor-mode data accesses are not subject to the U-mode pointer\nmasking (that is governed by menvcfg.PMM, which the kernel does not set),\nso hardware does not strip the tag for the kernel's own access.  With\nSv57 and PMLEN=16 the tag bits overlap the canonical-address bits, so a\ntagged pointer can name a canonical kernel virtual address (e.g. in the\nlinear map) whose untagged form is a valid user address.  An unprivileged\nprocess can thus make FUTEX_WAKE_OP perform an atomic read-modify-write on\nan arbitrary kernel address, with the matching FUTEX_OP_CMP_* result\nserving as a read oracle.\n\nget_user()/put_user()/raw_copy_{to,from}_user() already untag the pointer\nafter the access_ok() check; do the same in the futex helpers so the\natomic operates on the address that was actually validated.","modified":"2026-10-26T02:33:08.488956546Z","published":"2026-10-23T12:20:47.859Z","database_specific":{"cna_assigner":"Linux","osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/99xxx/CVE-2026-99016.json"},"references":[{"type":"WEB","url":"https://git.kernel.org/stable/c/2e5c80bbc062a8dda33e687ebf7be8f074ee4f7d"},{"type":"WEB","url":"https://git.kernel.org/stable/c/405290be962b32eec842776fbe3bdf81f15b1676"},{"type":"WEB","url":"https://git.kernel.org/stable/c/8e48d8d51ab37b7decfbff3e2844e027a52ad6ea"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/99xxx/CVE-2026-99016.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-99016"},{"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":"2e1743085887ba3f553c2bb472a75a3ff744b242"},{"fixed":"2e5c80bbc062a8dda33e687ebf7be8f074ee4f7d"},{"fixed":"8e48d8d51ab37b7decfbff3e2844e027a52ad6ea"},{"fixed":"405290be962b32eec842776fbe3bdf81f15b1676"}]}],"database_specific":{"source":"https://storage.googleapis.com/osv-test-cve-osv-conversion/osv-output/CVE-2026-99016.json"}},{"package":{"name":"Kernel","ecosystem":"Linux"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"6.13.0"},{"fixed":"6.18.57"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.19.0"},{"fixed":"7.2.11"}]}],"database_specific":{"source":"https://storage.googleapis.com/osv-test-cve-osv-conversion/osv-output/CVE-2026-99016.json"}}],"schema_version":"1.9.2","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H"}]}