CVE-2025-40271 深度分析：Linux proc 文件系统红黑树 UAF 漏洞

CVE-2025-40271 深度分析：Linux proc 文件系统红黑树 UAF 漏洞

📅 2025年 🏷️ Linux Kernel / CWE-416 📊 高危 🔗 CVE-2025-40271

摘要：本文对 CVE-2025-40271 展开深度技术分析。这是 Linux 内核 proc 文件系统中一处 use-after-free（UAF）漏洞，根因位于 fs/proc/generic.c 的 remove_proc_entry() 函数：开发者在调用 rb_erase() 将 proc_dir_entry 节点从红黑树中摘除后，没有调用 RB_CLEAR_NODE() 清空节点残留的父子指针。该缺陷使 proc_readdir_de() 在并发遍历 /proc 目录时，可能经由被释放节点的残留指针继续追踪红黑树，最终造成 UAF。官方修复补丁为 commit 895b4c0c79b092d732544011c3cecaf7322c36a1，它引入 pde_erase() 辅助函数，在摘除节点后立即清除节点链接。该漏洞可被本地攻击者利用，实现权限提升、内核崩溃，甚至容器逃逸。

📌 漏洞概述

⚠️ 核心判断：这是一个典型的“状态清理缺失”引发的 UAF

🕵️ 检测指纹规则

🛡️ Semgrep 审计规则: CVE-2025-40271.yaml

rules:
  - id: CVE-2025-40271-proc-uaf-c
    languages: [c]
    severity: ERROR
    message: "Potential use-after-free in proc_readdir_de() due to missing RB_CLEAR_NODE() after rb_erase() in remove_proc_entry(). This can lead to local privilege escalation."
    patterns:
      - pattern: rb_erase(...)
      - pattern-not: RB_CLEAR_NODE(...)
    fix: "pde_erase() helper that calls RB_CLEAR_NODE() after rb_erase();
or add RB_CLEAR_NODE() after each rb_erase() call"
    metadata:
      cwe: "CWE-416"
      owasp: "A8: Software and Data Integrity Failures"
      technology: linux-kernel
      references:
        - "https://nvd.nist.gov/vuln/detail/CVE-2025-40271"
        - "https://git.kernel.org/linus/895b4c0c79b092d732544011c3cecaf7322c36a1"
  - id: CVE-2025-40271-proc-concurrent-c
    languages: [c]
    severity: ERROR
    message: "Concurrent access to proc_dir_entry via getdents64() while removing proc entries can cause use-after-free. Race condition in proc_readdir_de() allows UAF."
    patterns:
      - pattern: getdents64(...)
      - pattern: remove_proc_entry(...)
    fix: "Use proper locking or pde_erase() helper;
ensure RB_CLEAR_NODE() is called after rb_erase()"
    metadata:
      cwe: "CWE-362"
      owasp: "A8: Software and Data Integrity Failures"
      technology: linux-kernel
      references:
        - "https://nvd.nist.gov/vuln/detail/CVE-2025-40271"

🛡️ CodeQL 审计规则: CVE-2025-40271.ql

/**
 * @kind problem
 * @id c/kernel-use-after-free/cve-2025-40271
 * @name Use-after-free in proc_readdir_de() due to missing RB_CLEAR_NODE
 * @description Concurrent proc_readdir_de() traversal via getdents64() can find a freed proc_dir_entry through pde_subdir_next() due to missing RB_CLEAR_NODE() after rb_erase() in remove_proc_entry(),
leading to use-after-free on struct proc_dir_entry.
 * @problem.severity error
 * @tags security
 *       external/cwe/cwe-416
 */
import cpp
import semmle.code.cpp.dataflow.DataFlow
import semmle.code.cpp.dataflow.TaintTracking

/**
 * A configuration for detecting use-after-free in proc_readdir_de().
 */
class ProcReaddirUseAfterFreeConfig extends TaintTracking::Configuration {
ProcReaddirUseAfterFreeConfig() {this = "ProcReaddirUseAfterFreeConfig" }override predicate isSource(DataFlow::Node source) {exists(FunctionCall fc |fc.getTarget().hasName("remove_proc_entry") and
      source.asExpr() = fc.getArgument(0)
    )
  }override predicate isSink(DataFlow::Node sink) {exists(FunctionCall fc |
(
        fc.getTarget().hasName("rb_next") or
        fc.getTarget().hasName("pde_subdir_next") or
        fc.getTarget().hasName("RB_EMPTY_NODE")
      ) and
      sink.asExpr() = fc.getArgument(0)
    )
  }override predicate isAdditionalTaintStep(DataFlow::Node node1,DataFlow::Node node2) {// RB_CLEAR_NODE is missing - the freed entry retains stale rb-links
    none()
  }}
from DataFlow::Node source,DataFlow::Node sink,DataFlow::Node free,ProcReaddirUseAfterFreeConfig config
where
  config.hasFlow(source,sink) and
  // The freed proc_dir_entry is passed to rb_next/pde_subdir_next/RB_EMPTY_NODE
  exists(FunctionCall rbNext |rbNext.getTarget().hasName("rb_next") and
    source = rbNext.getArgument(0)
  )
select sink,
"Use-after-free in proc_readdir_de(): freed proc_dir_entry accessed via $@",free,"remove_proc_entry"

🤖 本文由漏洞情报系统自动聚合生成 · 2026-08-01 12:06 · 数据源: NVD/GitHub-Advisory/OSV/CISA-KEV/Exploit-DB/PoC-in-GitHub + 检测规则库