在完美运行的程序中检测到缓冲区溢出(显然) [英] Buffer overflow detected in a program that runs flawlessly ( apparently)
问题描述
在包含as，bs和cs的字符串上，我们可以执行以下操作.我们可以将任意两个相邻的不同字符替换为第三个字符.例如，"ab"被还原为"c"，"ba"也被还原，依此类推.我编写了这段代码，以对t个字符串(t< = 100)和最大字符串长度= 100
On a string containing as, bs and cs, we can perform the following operation. We can take any two adjacent different characters and replace them by the third. For example, 'ab' gets reduced to 'c' and so does 'ba' and so on. I wrote this code to perform the following operation on t strings (t<=100) and max length of strings = 100
#include<stdio.h>
#include<string.h>
#include<stdlib.h>
int redlen(char string[100][100], int x)
{
int g, checker; checker = 1;
for(; checker; )
{
checker = 0;
for(int i = 0;string[x][i]!='\0'; i++)
{
if((string[x][i]=='a' && string[x][i+1]=='b') || (string[x][i]=='b' && string[x][i+1]=='a'))
{
string[x][i]='c';
checker = 1;
for(g = i+1; string[x][g]!='\0'; g++)
{
string[x][g]=string[x][g+1];
}
i = 0;
}
else if((string[x][i]=='b' && string[x][i+1]=='c') || (string[x][i]=='c' && string[x][i+1]=='b'))
{
string[x][i]='a';
checker = 1;
for(g = i+1; string[x][g]!='\0'; g++)
{
string[x][g]=string[x][g+1];
}
i = 0;
}
else if((string[x][i]=='a' && string[x][i+1]=='c') || (string[x][i]=='c' && string[x][i+1]=='a'))
{
string[x][i]='b';
checker = 1;
for(g = i+1; string[x][g]!='\0'; g++)
{
string[x][g]=string[x][g+1];
}
i = 0;
}
}
}
return strlen(string[x]);
}
void main()
{
int t; char r[3];
gets(r);
t = atoi(r);
char string[100][100];
int i;
for(i = 0; i<t; i++)
{
gets(string[i]);
}
int printval;
for(i = 0; i<t; i++)
{
printval = redlen(string, i);
printf("%d",printval);
printf(" \n");
}
}
在问题的示例案例以及我自己开发的案例中，它都可以很好地工作.但是当我在线提交时，它仅通过了十个案例中的一个，在其余案例中，此消息弹出了.
It worked fine on the sample case of the problem and also on the cases I developed on my own. But when I submitted it online, it passed only one of the ten cases, and in the rest, this message popped up.
*** buffer overflow detected ***: /run-DkQcMiKXhWz9LjirrRnu/solution terminated
======= Backtrace: =========
/lib/i386-linux-gnu/tls/i686/nosegneg/libc.so.6(__fortify_fail+0x45)[0xb76df045]
/lib/i386-linux-gnu/tls/i686/nosegneg/libc.so.6(+0x102e1a)[0xb76dde1a]
/lib/i386-linux-gnu/tls/i686/nosegneg/libc.so.6(__gets_chk+0x165)[0xb76ddd85]
/run-DkQcMiKXhWz9LjirrRnu/solution[0x8048436]
/lib/i386-linux-gnu/tls/i686/nosegneg/libc.so.6(__libc_start_main+0xf3)[0xb75f44d3]
/run-DkQcMiKXhWz9LjirrRnu/solution[0x80484e9]
======= Memory map: ========
08048000-08049000 r-xp 00000000 ca:02 15613970 /run-DkQcMiKXhWz9LjirrRnu/solution
08049000-0804a000 r--p 00000000 ca:02 15613970 /run-DkQcMiKXhWz9LjirrRnu/solution
0804a000-0804b000 rw-p 00001000 ca:02 15613970 /run-DkQcMiKXhWz9LjirrRnu/solution
084e2000-08503000 rw-p 00000000 00:00 0 [heap]
b75ba000-b75d6000 r-xp 00000000 ca:01 394527 /lib/i386-linux-gnu/libgcc_s.so.1
b75d6000-b75d7000 r--p 0001b000 ca:01 394527 /lib/i386-linux-gnu/libgcc_s.so.1
b75d7000-b75d8000 rw-p 0001c000 ca:01 394527 /lib/i386-linux-gnu/libgcc_s.so.1
b75d8000-b75db000 rw-p 00000000 00:00 0
b75db000-b777e000 r-xp 00000000 ca:01 394522 /lib/i386-linux- gnu/tls/i686/nosegneg/libc-2.15.so
b777e000-b777f000 ---p 001a3000 ca:01 394522 /lib/i386-linux-gnu/tls/i686/nosegneg/libc-2.15.so
b777f000-b7781000 r--p 001a3000 ca:01 394522 /lib/i386-linux-gnu/tls/i686/nosegneg/libc-2.15.so
b7781000-b7782000 rw-p 001a5000 ca:01 394522 /lib/i386-linux-gnu/tls/i686/nosegneg/libc-2.15.so
b7782000-b7789000 rw-p 00000000 00:00 0
b7789000-b778a000 r-xp 00000000 00:00 0 [vdso]
b778a000-b77aa000 r-xp 00000000 ca:01 400153 /lib/i386-linux-gnu/ld-2.15.so
b77aa000-b77ab000 r--p 0001f000 ca:01 400153 /lib/i386-linux-gnu/ld-2.15.so
b77ab000-b77ac000 rw-p 00020000 ca:01 400153 /lib/i386-linux-gnu/ld-2.15.so
bfe6e000-bfe8f000 rw-p 00000000 00:00 0 [stack]
Aborted (core dumped)
并非在所有情况下都完全相同，但几乎相同.请帮忙.
It wasn't exactly same in all the cases, but pretty much the same. Please help.
推荐答案
int t; char r[3];
gets(r);
永远不要使用gets功能.在这种情况下，如果它接收到超过3个字符(包括终止的空字符)，则会出现缓冲区溢出.
Never ever use gets function. In this case if it receives more than 3 characters (including the terminating null character) you get a buffer overflow.
gets在当前标准(C11)中已被删除，而在先前的标准(C99)中已弃用.
gets has been removed in the current Standard (C11) and was deprecated in the previous Standard (C99).
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