CODEWITHSUNDEEP
cstringpointersbuffer-overflowstrcmp
shd293
shd293

Reputation: 97

Segmentation Fault in the Following Program for string comparisons

I am getting segmentation fault for the following code. The logic of the program that it should accept the correct password ("abcd") and it should deny access if entered any other password, but I am still getting a segmentation fault after I enter wrong password (eg: "acdc" or "ancgff").I get proper response for passwords like "abc" or "xyz" where I get "access denied" message.

Please help me , unable to understand why I am getting this error?

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

int check(char *password)
{
    char pin_buffer[4];

    int authority = 0;

    strcpy(pin_buffer,password);

    if(strcmp(pin_buffer,"abcd")==0)

        authority=1;
    return authority;

}

int main(int argc, char *argv[])
{   
    if(argc < 1)
    {           
        printf(argv[0]);
        exit(0);
    }

    if(check(argv[1]))
    {
       printf("access granted");
    } 
    else
    {
        printf("access denied};
}

Upvotes: 0

Views: 63

Answers (1)

Sourav Ghosh
Sourav Ghosh

Reputation: 134346

You define

char pin_buf[4];

with a pre-decided size of 4 and then, without any check, you use

 strcpy(pin_buf,pin);

the moment pin has more than 3 elements (and a terminating null), you'll be overrunning the boundary of allocated memory while attempoting to copy which causes undefined behavior.

That is why, you observe

"...I am still getting a segmentation fault after I enter wrong password (eg: "acdc" or "ancgff").I get proper response for passwords like "abc" or "xyz""

That said, you don't need the pin_buf at all. The operations you intend to perform can be done with pin itself.

Upvotes: 3

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