riscv: futex: untag the user pointer before the atomic access
Summary
| CVE | CVE-2026-99016 |
|---|---|
| State | PUBLISHED |
| Assigner | Linux |
| Source Priority | CVE Program / NVD first with legacy fallback |
| Published | 2026-10-23 13:17:24 UTC |
| Updated | 2026-10-24 14:16:52 UTC |
| Description | In the Linux kernel, the following vulnerability has been resolved: riscv: futex: untag the user pointer before the atomic access access_ok() checks untagged_addr(uaddr), but arch_futex_atomic_op_inuser() and futex_atomic_cmpxchg_inatomic() hand the raw uaddr to the inline asm amoswap/amoadd/.../lr.w+sc.w through the "+m" (*uaddr) operand. When the tagged address ABI is enabled (CONFIG_RISCV_ISA_SUPM, prctl PR_SET_TAGGED_ADDR_CTRL with PMLEN != 0), those two addresses differ: a user pointer whose top PMLEN bits hold a tag passes access_ok() after untagging, but the atomic is then performed on the still-tagged raw address. Supervisor-mode data accesses are not subject to the U-mode pointer masking (that is governed by menvcfg.PMM, which the kernel does not set), so hardware does not strip the tag for the kernel's own access. With Sv57 and PMLEN=16 the tag bits overlap the canonical-address bits, so a tagged pointer can name a canonical kernel virtual address (e.g. in the linear map) whose untagged form is a valid user address. An unprivileged process can thus make FUTEX_WAKE_OP perform an atomic read-modify-write on an arbitrary kernel address, with the matching FUTEX_OP_CMP_* result serving as a read oracle. get_user()/put_user()/raw_copy_{to,from}_user() already untag the pointer after the access_ok() check; do the same in the futex helpers so the atomic operates on the address that was actually validated. |
Risk And Classification
Primary CVSS: v3.1 7.8 HIGH from 416baaa9-dc9f-4396-8d5f-8c081fb06d67
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
| Version | Source | Type | Score | Severity | Vector |
|---|---|---|---|---|---|
| 3.1 | 416baaa9-dc9f-4396-8d5f-8c081fb06d67 | Secondary | 7.8 | HIGH | CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H |
| 3.1 | CNA | DECLARED | 7.8 | HIGH | CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H |
CVSS v3.1 Breakdown
Attack Vector
LocalAttack Complexity
LowPrivileges Required
LowUser Interaction
NoneScope
UnchangedConfidentiality
HighIntegrity
HighAvailability
HighCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Vendor Declared Affected Products
| Source | Vendor | Product | Version | Platforms |
|---|---|---|---|---|
| CNA | Linux | Linux | affected 2e1743085887ba3f553c2bb472a75a3ff744b242 2e5c80bbc062a8dda33e687ebf7be8f074ee4f7d git | Not specified |
| CNA | Linux | Linux | affected 2e1743085887ba3f553c2bb472a75a3ff744b242 8e48d8d51ab37b7decfbff3e2844e027a52ad6ea git | Not specified |
| CNA | Linux | Linux | affected 2e1743085887ba3f553c2bb472a75a3ff744b242 405290be962b32eec842776fbe3bdf81f15b1676 git | Not specified |
| CNA | Linux | Linux | affected 6.13 | Not specified |
| CNA | Linux | Linux | unaffected 6.13 semver | Not specified |
| CNA | Linux | Linux | unaffected 6.18.57 6.18.* semver | Not specified |
| CNA | Linux | Linux | unaffected 7.2.11 7.2.* semver | Not specified |
| CNA | Linux | Linux | unaffected 7.3 * original_commit_for_fix | Not specified |
References
| Reference | Source | Link | Tags |
|---|---|---|---|
| git.kernel.org/stable/c/405290be962b32eec842776fbe3bdf81f15b1676 | 416baaa9-dc9f-4396-8d5f-8c081fb06d67 | git.kernel.org | |
| git.kernel.org/stable/c/8e48d8d51ab37b7decfbff3e2844e027a52ad6ea | 416baaa9-dc9f-4396-8d5f-8c081fb06d67 | git.kernel.org | |
| git.kernel.org/stable/c/2e5c80bbc062a8dda33e687ebf7be8f074ee4f7d | 416baaa9-dc9f-4396-8d5f-8c081fb06d67 | git.kernel.org | |
| CVE Program record | CVE.ORG | www.cve.org | canonical |
| NVD vulnerability detail | NVD | nvd.nist.gov | canonical, analysis |
No vendor comments have been submitted for this CVE.
There are currently no legacy QID mappings associated with this CVE.