{ "dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": { "cveId": "CVE-2025-38434", "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "state": "PUBLISHED", "assignerShortName": "Linux", "dateReserved": "2025-04-16T04:51:24.015Z", "datePublished": "2025-07-25T14:32:08.089Z", "dateUpdated": "2026-08-05T12:01:51.423Z" }, "containers": { "cna": { "providerMetadata": { "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "shortName": "Linux", "dateUpdated": "2026-08-05T12:01:51.423Z" }, "descriptions": [ { "lang": "en", "value": "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." } ], "metrics": [ { "cvssV3_1": { "version": "3.1", "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H", "baseScore": 7.8, "baseSeverity": "HIGH" }, "scenarios": [ { "lang": "en", "value": "AV:L - The bug is reached only through local syscalls (futex(), read()/write() with user iovecs, io_uring fixed-buffer registration) in which the attacker supplies a crafted userspace virtual address; there is no network path to the vulnerable get_user_pages_fast() check.\nAC:L - Exploitation is fully deterministic — the attacker simply passes an address in [TASK_SIZE, LONG_MAX] to a gup_fast user; there is no race and no attacker-uncontrolled condition on an affected RISC-V 64-bit kernel.\nPR:L - Any unprivileged local user can invoke the affected syscalls (futex, read/write, io_uring); no capabilities or elevated privileges are required.\nUI:N - The attacker triggers the flaw entirely through their own syscalls with no action required from any other user.\nS:U - The vulnerability and its impact are both contained within the OS kernel's security authority; this is a standard in-kernel memory-safety boundary bug, not a VM/sandbox escape.\nC:H - The flaw lets an unprivileged user pin present kernel PTEs (the generic pte_access_permitted() does not check _PAGE_USER) and read arbitrary kernel memory out via write()-style transfers, a full kernel-memory disclosure primitive.\nI:H - Using FOLL_WRITE paths (e.g. read() into the crafted buffer) the same walk pins writable kernel pages, allowing attacker-controlled data to be written into kernel memory — an arbitrary kernel write enabling privilege escalation.\nA:H - Walking into the kernel half of the page tables and corrupting or dereferencing kernel structures can trivially oops/panic the kernel." } ] } ], "affected": [ { "product": "Linux", "vendor": "Linux", "defaultStatus": "unaffected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": [ "arch/riscv/include/asm/pgtable.h" ], "versions": [ { "version": "ad5643cf2f699989daa85d909403febd6712fccb", "lessThan": "fe30c30bf3bb68d4a4d8c7c814769857b5c973e6", "status": "affected", "versionType": "git" }, { "version": "ad5643cf2f699989daa85d909403febd6712fccb", "lessThan": "f8b1898748dfeb4f9b67b6a6d661f354b9de3523", "status": "affected", "versionType": "git" }, { "version": "ad5643cf2f699989daa85d909403febd6712fccb", "lessThan": "890ba5be6335dbbbc99af14ea007befb5f83f174", "status": "affected", "versionType": "git" } ] }, { "product": "Linux", "vendor": "Linux", "defaultStatus": "affected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": [ "arch/riscv/include/asm/pgtable.h" ], "versions": [ { "version": "6.10", "status": "affected" }, { "version": "0", "lessThan": "6.10", "status": "unaffected", "versionType": "semver" }, { "version": "6.12.36", "lessThanOrEqual": "6.12.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.15.5", "lessThanOrEqual": "6.15.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.16", "lessThanOrEqual": "*", "status": "unaffected", "versionType": "original_commit_for_fix" } ] } ], "cpeApplicability": [ { "nodes": [ { "operator": "OR", "negate": false, "cpeMatch": [ { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.10", "versionEndExcluding": "6.12.36" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.10", "versionEndExcluding": "6.15.5" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.10", "versionEndExcluding": "6.16" } ] } ] } ], "references": [ { "url": "https://git.kernel.org/stable/c/fe30c30bf3bb68d4a4d8c7c814769857b5c973e6" }, { "url": "https://git.kernel.org/stable/c/f8b1898748dfeb4f9b67b6a6d661f354b9de3523" }, { "url": "https://git.kernel.org/stable/c/890ba5be6335dbbbc99af14ea007befb5f83f174" } ], "title": "Revert \"riscv: Define TASK_SIZE_MAX for __access_ok()\"", "x_generator": { "engine": "bippy-1.2.0" } } } }