{"id":"CVE-2025-38434","summary":"Revert \"riscv: Define TASK_SIZE_MAX for __access_ok()\"","details":"In the Linux kernel, the following vulnerability has been resolved:\n\nRevert \"riscv: Define TASK_SIZE_MAX for __access_ok()\"\n\nThis reverts commit ad5643cf2f69 (\"riscv: Define TASK_SIZE_MAX for\n__access_ok()\").\n\nThis commit changes TASK_SIZE_MAX to be LONG_MAX to optimize access_ok(),\nbecause the previous TASK_SIZE_MAX (default to TASK_SIZE) requires some\ncomputation.\n\nThe reasoning was that all user addresses are less than LONG_MAX, and all\nkernel addresses are greater than LONG_MAX. Therefore access_ok() can\nfilter kernel addresses.\n\nAddresses between TASK_SIZE and LONG_MAX are not valid user addresses, but\naccess_ok() let them pass. That was thought to be okay, because they are\nnot valid addresses at hardware level.\n\nUnfortunately, one case is missed: get_user_pages_fast() happily accepts\naddresses between TASK_SIZE and LONG_MAX. futex(), for instance, uses\nget_user_pages_fast(). This causes the problem reported by Robert [1].\n\nTherefore, revert this commit. TASK_SIZE_MAX is changed to the default:\nTASK_SIZE.\n\nThis unfortunately reduces performance, because TASK_SIZE is more expensive\nto compute compared to LONG_MAX. But correctness first, we can think about\noptimization later, if required.","modified":"2026-04-02T12:47:58.468959Z","published":"2025-07-25T14:32:08.089Z","database_specific":{"osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2025/38xxx/CVE-2025-38434.json","cna_assigner":"Linux"},"references":[{"type":"WEB","url":"https://git.kernel.org/stable/c/890ba5be6335dbbbc99af14ea007befb5f83f174"},{"type":"WEB","url":"https://git.kernel.org/stable/c/f8b1898748dfeb4f9b67b6a6d661f354b9de3523"},{"type":"WEB","url":"https://git.kernel.org/stable/c/fe30c30bf3bb68d4a4d8c7c814769857b5c973e6"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2025/38xxx/CVE-2025-38434.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2025-38434"},{"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":"ad5643cf2f699989daa85d909403febd6712fccb"},{"fixed":"fe30c30bf3bb68d4a4d8c7c814769857b5c973e6"},{"fixed":"f8b1898748dfeb4f9b67b6a6d661f354b9de3523"},{"fixed":"890ba5be6335dbbbc99af14ea007befb5f83f174"}]}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2025-38434.json"}}],"schema_version":"1.7.5"}