读取文件并转换其字符的 C 程序会产生双重释放或损坏错误

Question

当执行我的程序时，我有这个错误：

*** Error in `./xorcipher': double free or corruption (!prev): 0x00000000024a1010 ***
======= Backtrace: =========
/lib/x86_64-linux-gnu/libc.so.6(+0x777e5)[0x7fe869b317e5]
/lib/x86_64-linux-gnu/libc.so.6(+0x8037a)[0x7fe869b3a37a]
/lib/x86_64-linux-gnu/libc.so.6(cfree+0x4c)[0x7fe869b3e53c]
/lib/x86_64-linux-gnu/libc.so.6(fclose+0x103)[0x7fe869b27363]
./xorcipher[0x4009de]
./xorcipher[0x400d68]
/lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0xf0)[0x7fe869ada830]
./xorcipher[0x4007b9]
======= Memory map: ========
00400000-00402000 r-xp 00000000 fd:01 1056628                            /home/user1/Dropbox/SCOLARITY/L2Informatique/S3/Projet/Projet xorcipher/Code/programme final/test/xorcipher
00601000-00602000 r--p 00001000 fd:01 1056628                            /home/user1/Dropbox/SCOLARITY/L2Informatique/S3/Projet/Projet xorcipher/Code/programme final/test/xorcipher
00602000-00603000 rw-p 00002000 fd:01 1056628                            /home/user1/Dropbox/SCOLARITY/L2Informatique/S3/Projet/Projet xorcipher/Code/programme final/test/xorcipher
024a1000-024c2000 rw-p 00000000 00:00 0                                  [heap]
7fe864000000-7fe864021000 rw-p 00000000 00:00 0 
7fe864021000-7fe868000000 ---p 00000000 00:00 0 
7fe8698a4000-7fe8698ba000 r-xp 00000000 fd:01 136064                     /lib/x86_64-linux-gnu/libgcc_s.so.1
7fe8698ba000-7fe869ab9000 ---p 00016000 fd:01 136064                     /lib/x86_64-linux-gnu/libgcc_s.so.1
7fe869ab9000-7fe869aba000 rw-p 00015000 fd:01 136064                     /lib/x86_64-linux-gnu/libgcc_s.so.1
7fe869aba000-7fe869c7a000 r-xp 00000000 fd:01 137277                     /lib/x86_64-linux-gnu/libc-2.23.so
7fe869c7a000-7fe869e7a000 ---p 001c0000 fd:01 137277                     /lib/x86_64-linux-gnu/libc-2.23.so
7fe869e7a000-7fe869e7e000 r--p 001c0000 fd:01 137277                     /lib/x86_64-linux-gnu/libc-2.23.so
7fe869e7e000-7fe869e80000 rw-p 001c4000 fd:01 137277                     /lib/x86_64-linux-gnu/libc-2.23.so
7fe869e80000-7fe869e84000 rw-p 00000000 00:00 0 
7fe869e84000-7fe869eaa000 r-xp 00000000 fd:01 137058                     /lib/x86_64-linux-gnu/ld-2.23.so
7fe86a089000-7fe86a08c000 rw-p 00000000 00:00 0 
7fe86a0a6000-7fe86a0a9000 rw-p 00000000 00:00 0 
7fe86a0a9000-7fe86a0aa000 r--p 00025000 fd:01 137058                     /lib/x86_64-linux-gnu/ld-2.23.so
7fe86a0aa000-7fe86a0ab000 rw-p 00026000 fd:01 137058                     /lib/x86_64-linux-gnu/ld-2.23.so
7fe86a0ab000-7fe86a0ac000 rw-p 00000000 00:00 0 
7ffea9648000-7ffea9669000 rw-p 00000000 00:00 0                          [stack]
7ffea96b5000-7ffea96b7000 r--p 00000000 00:00 0                          [vvar]
7ffea96b7000-7ffea96b9000 r-xp 00000000 00:00 0                          [vdso]
ffffffffff600000-ffffffffff601000 r-xp 00000000 00:00 0                  [vsyscall]
Aborted

问题似乎出在 xor 函数中，但我想不出是什么问题。根据 this，我的问题似乎是由取消引用的指针引起的。但根据 valgrind，这是一个开放的不可取消错误（我不知道它是什么，也无法在 google 上找到任何相关信息）。另一方面，我没有编译错误。

我的代码有什么问题？

程序如下：

#include <stdio.h>
#include <string.h>
#include <stdlib.h>

void xor(char* name_file_in,char* name_file_out,char* name_key)
{
    FILE *file_in;//file to encrypt
    FILE *file_out;//encrypted file
    unsigned char read_char;//character of the file
    int count_char=0;//count number of characters in file
    file_in=fopen(name_file_in,"r");
    file_out=fopen(name_file_out,"w");

    while ( fscanf(file_in,"%c",&read_char) != EOF)//each character of in file is read
    {
        read_char=read_char^name_key[count_char%strlen(name_key)];//read_char is encrypted according to key's length's modulo
        fputc(read_char,file_out);//writing character to out file
        count_char++;
    }
    fclose(file_in);
    fclose(file_in);
}

int main(int argc,char* argv[])
{   
    xor(argv[1],argv[2],argv[3]);
    return(0);
}

Answer 1

您正在关闭文件两次：

fclose(file_in);
fclose(file_in);

这是未定义的行为。

注意：我用 valgrind 只花了 5 秒就看到了...编译调试时使用 -g！

Answer 2

您必须以二进制方式读写文件，即使它是文本文件。这是因为 XOR 运算符可能导致零字节，这会破坏文本模式下的读取例程。

file_in = fopen(name_file_in, "rb");
file_out = fopen(name_file_out, "wb");

此外，您必须检查以确保输入有效

if (!name_file_in) return;
if (!name_file_out) return;
if (!name_key) return;

如果文件句柄无效则不要继续

void xor(char* name_file_in, char* name_file_out, char* name_key)
{
    if (!name_file_in) return;
    if (!name_file_out) return;
    if (!name_key) return;

    FILE *file_in;
    FILE *file_out;
    unsigned char read_char;
    int count_char = 0;

    file_in = fopen(name_file_in, "rb");
    file_out = fopen(name_file_out, "wb");

    if(file_in && file_out)
    {
        while(fscanf(file_in, "%c", &read_char) > 0)
        {
            read_char ^= name_key[count_char%strlen(name_key)];
            fputc(read_char, file_out);//writing character to out file
            count_char++;
        }
    }

    if (file_in)
        fclose(file_in);

    if (file_out)
        fclose(file_out);
}

您可以将循环更改为 for(int i = 0; i < argc - 1; i++){...}，因为您在每次迭代中访问 argv[i+1]。

读取文件并转换其字符的 C 程序会产生双重释放或损坏错误

Program in C who reads a file and transform his characters produces a double free or corruption error

c

debugging

valgrind

corruption

double-free