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CERT C:Rec.FIO02-C

Canonicalize path names originating from tainted sources

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描述

规则定义

Canonicalize path names originating from tainted sources.1

Polyspace 实现

规则检查项检查是否存在易受攻击的路径操作。

示例

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问题

易受攻击的路径操作检测相对或绝对路径遍历。如果路径遍历包含受污染的源，或者您使用该路径打开/创建文件，Bug Finder 会引发缺陷。

风险

相对路径元素（例如 ".."）可能会解析为目标文件夹之外的位置。绝对路径元素（例如 "/abs/path"）也可以解析为目标文件夹之外的位置。

攻击者可以使用这些类型的路径遍历元素遍历文件系统的其余部分，并访问其他文件或文件夹。

修复

避免使用易受攻击的路径遍历元素，例如 /../ 和 /abs/path/。尽可能使用固定的文件名和位置。

示例 - 相对路径遍历
# include <stdio.h>
# include <string.h>
# include <wchar.h>
# include <sys/types.h>
# include <sys/stat.h>
# include <fcntl.h>
# include <unistd.h>
# include <stdlib.h>
# define BASEPATH "/tmp/"
# define FILENAME_MAX 512

static void Relative_Path_Traversal(void)
{
    char * data;
    char data_buf[FILENAME_MAX] = BASEPATH;
    char sub_buf[FILENAME_MAX];

    if (fgets(sub_buf, FILENAME_MAX, stdin) == NULL) exit (1);
    data = data_buf;
    strcat(data, sub_buf);

    FILE *file = NULL;
    file = fopen(data, "wb+");  //Noncompliant
    if (file != NULL) fclose(file);
}

int path_call(void){
    Relative_Path_Traversal();
}

此示例从 "/tmp/" 打开一个文件，但使用的是相对于该文件的相对路径。当 fopen 打开文件时，外部用户可以操作此相对路径。

更正 - 使用固定文件名

一种可能的更正方法是使用固定文件名代替相对路径。此示例使用 file.txt。

# include <stdio.h>
# include <string.h>
# include <wchar.h>
# include <sys/types.h>
# include <sys/stat.h>
# include <fcntl.h>
# include <unistd.h>
# include <stdlib.h>
# define BASEPATH "/tmp/"
# define FILENAME_MAX 512

static void Relative_Path_Traversal(void)
{
    char * data;
    char data_buf[FILENAME_MAX] = BASEPATH;
    data = data_buf;

    /* FIX: Use a fixed file name */
    strcat(data, "file.txt");
    FILE *file = NULL;
    file = fopen(data, "wb+");  
    if (file != NULL) fclose(file);
}

int path_call(void){
    Relative_Path_Traversal();
}

检查信息

组：Rec.09.输入输出 (FIO)

版本历史记录

在 R2019a 中推出

另请参阅

主题

外部网站

1 This software has been created by MathWorks incorporating portions of: the “SEI CERT-C Website,” © 2017 Carnegie Mellon University, the SEI CERT-C++ Web site © 2017 Carnegie Mellon University, ”SEI CERT C Coding Standard – Rules for Developing safe, Reliable and Secure systems – 2016 Edition,” © 2016 Carnegie Mellon University, and “SEI CERT C++ Coding Standard – Rules for Developing safe, Reliable and Secure systems in C++ – 2016 Edition” © 2016 Carnegie Mellon University, with special permission from its Software Engineering Institute.

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This software and associated documentation has not been reviewed nor is it endorsed by Carnegie Mellon University or its Software Engineering Institute.