Question

I have a code that scans an entire directory for .wor files, and extract info from them. When I run the file on a directory with 5 .wor files, it works perfectly. But when i try to run it on a directory with 70+ .wor files, it gives me an “Memery fault(coredump” error.

So i tried to debug the code with gdb, and here is what i got:

Program received signal SIGSEGV, Segmentation fault.
0x7af9fcbc in _sbrk () from /usr/lib/libc.2
(gdb) bt
#0  0x7af9fcbc in _sbrk () from /usr/lib/libc.2
#1  0x7af9db7c in _sigfillset () from /usr/lib/libc.2
#2  0x7af9bfe8 in __thread_callback_np () from /usr/lib/libc.2
#3  0x7afa0e64 in malloc () from /usr/lib/libc.2
#4  0x7b001160 in _findbuf () from /usr/lib/libc.2
#5  0x7afff7f4 in _filbuf () from /usr/lib/libc.2
#6  0x7afff404 in __fgets_unlocked () from /usr/lib/libc.2
#7  0x7afff5fc in fgets () from /usr/lib/libc.2
#8  0x2c14 in main (argc=1, argv=0x7dff11b4) at book2.c:99

I looked at line 99 and i have the command: while( fgets(buff, 100,fs) != NULL ), I do not know c well enough to find where the error is, any help here would be really appreciated, thanks in advance!

Here is my code:

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <sys/types.h>
#include <dirent.h>
#include <unistd.h>
#include <errno.h>


int main(int argc, char **argv) {

char directory[100];
char buff[100];
char delims[] = " :=";
char *result = NULL;
char *customer;
char *device;
char *testprog;
char *software;
char *dutboardid;
char *corlbox;
char *testerid;
char *temp;
char *buffer;
int i=0;
DIR * FD;
struct dirent* in_file;
int c=0;


printf ("Enter directory:");                                   
    scanf ("%s",directory);


    FILE * ft = fopen ( "workorderlist.csv", "w" ) ;    /* Open file to write to*/
    if ( ft == NULL )
    {
           puts ( "Cannot open target file" ) ;
           exit( 1 ) ;
    }


fprintf (ft, "Work Order,Customer,Device,Test Program,Software,DUT_board_id,Corl box, Tempurature, Test Station\n");



/* Open Directory*/

if (NULL == (FD = opendir (directory))) 
    {

        puts ("Cannot open directory");

    return 1;
    }


    while ((in_file = readdir(FD))) 
    {

    if (!strcmp (in_file->d_name, "."))
        continue;
    if (!strcmp (in_file->d_name, ".."))    
        continue;



    /* Open files to read from  */

buffer = (char*) malloc (200);
sprintf(buffer, "%s/%s", directory, in_file->d_name);


size_t len = strlen(buffer);
if (len >= 4 && memcmp(buffer + len - 4, ".wor", 4) == 0)   /* checks if file ends with .wor */
{

FILE * fs = fopen(buffer, "r");       /* open file to read */

customer = "0";
device = "0";
testprog = "0";
software = "0";
dutboardid = "0";
corlbox = "0";
testerid = "0";
temp = "0";

    if (fs == NULL)
    {
        puts ("Cannot open source file");

        return 1;
    }

    /* Scanning each file for targeted words: */


while( fgets(buff, 100,fs) != NULL )      
{   



 result = strtok( buff, delims );          
    while(result != NULL){   


            if((strcmp(result,"Customer")==0)){ 
        result = strtok(NULL,delims);  
        customer = (char*)malloc((strlen(result)+1)*sizeof(char));
        strcpy(customer, result);
        for(i=0;i<strlen(customer)+1;i++){ if(customer[i] == '\n') break; }
        customer[i] = ' ';
        }

            if((strcmp(result,"name")==0)){ 
        result = strtok(NULL,delims);  
        customer = (char*)malloc((strlen(result)+1)*sizeof(char));
        strcpy(customer, result);
        for(i=0;i<strlen(customer)+1;i++){ if(customer[i] == '\n') break; }
        customer[i] = ' ';
        }


            if(strcmp(result,"device")==0){ 
        result = strtok(NULL,delims);  
        device = (char*)malloc((strlen(result)+1)*sizeof(char));
        strcpy(device, result);
        for(i=0;i<strlen(device)+1;i++){ if(device[i] == '\n') break; } 
        device[i] = ' ';
        }


            if(strcmp(result,"test_prog")==0 || strcmp(result, "testprog")==0){ 
        result = strtok(NULL,delims);  
        testprog = (char*)malloc((strlen(result)+1)*sizeof(char));
        strcpy(testprog, result);
        for(i=0;i<strlen(testprog)+1;i++){ if(testprog[i] == '\n') break; } 
        testprog[i] = ' ';
        }


            if(strcmp(result,"Rev")==0 || strcmp(result,"use")==0){ 
        result = strtok(NULL,delims);  
        software = (char*)malloc((strlen(result)+1)*sizeof(char));
        strcpy(software, result);
        for(i=0;i<strlen(software)+1;i++){ if(software[i] == '\n') break; } 
        software[i] = ' ';
        }

        if(strcmp(result,"rev")==0){ 
        result = strtok(NULL,delims);  
        software = (char*)malloc((strlen(result)+1)*sizeof(char));
        strcpy(software, result);
        for(i=0;i<strlen(software)+1;i++){ if(software[i] == '\n') break; } 
        software[i] = ' ';
        }

            if(strcmp(result,"DUT_board_id")==0){ 
        result = strtok(NULL,delims);  
        dutboardid = (char*)malloc((strlen(result)+1)*sizeof(char));
        strcpy(dutboardid, result);
        for(i=0;i<strlen(dutboardid)+1;i++){ if(dutboardid[i] == '\n') break; } 
        dutboardid[i] = ' ';
        }                   

            if(strcmp(result,"box")==0){ 
        result = strtok(NULL,delims);  
        corlbox = (char*)malloc((strlen(result)+1)*sizeof(char));
        strcpy(corlbox, result);
        for(i=0;i<strlen(corlbox)+1;i++){ if(corlbox[i] == '\n') break; } 
        corlbox[i] = ' ';
        }

        if(strcmp(result,"Tester_id")==0){ 
        result = strtok(NULL,delims);  
        testerid = (char*)malloc((strlen(result)+1)*sizeof(char));
        strcpy(testerid, result);
        for(i=0;i<strlen(testerid)+1;i++){ if(testerid[i] == '\n') break; } 
        testerid[i] = ' ';
        }

        if(strcmp(result,"@")==0){ 
        result = strtok(NULL,delims);  
        temp = (char*)malloc((strlen(result)+1)*sizeof(char));
        strcpy(temp, result);
        for(i=0;i<strlen(temp)+1;i++){ if(temp[i] == '\n') break; } 
        temp[i] = ' ';
        }


        result = strtok(NULL,delims);
    }

}

if (strcmp(customer, "0")==0){
customer = "N/A";
}
if (strcmp(device, "0")==0){
device = "N/A";
}
if (strcmp(testprog, "0")==0){
testprog = "N/A";
}
if (strcmp(software,"0")==0){
software = "N/A";
}
if (strcmp(dutboardid, "0")==0){
dutboardid = "N/A";
}
if (strcmp(corlbox, "0")==0){
corlbox = "N/A";
}
if (strcmp(testerid, "0")==0){
testerid = "N/A";
}
if (strcmp(temp, "0")==0){
temp = "N/A";
}

fprintf (ft, "%s,%s,%s,%s,%s,%s,%s,%s,%s\n", in_file->d_name, customer, device, testprog, software, dutboardid, corlbox, temp, testerid);


printf(in_file->d_name);
printf("\n");
fclose (fs) ;
c++;

}
}
printf("Total Workorders Found: %d (Info saved to workorderlist.csv)\n", c);
    fclose ( ft ) ;
return 0;

}

Answer 1

If we take this example:

customer = (char*)malloc((strlen(result)+1)*sizeof(char));
strcpy(customer, result);
for(i=0;i<strlen(customer)+1;i++){ if(customer[i] == '\n') break; }
customer[i] = ' ';

It copies result, which takes up strlen(result)+1 bytes. You then copy in result into customer. After that, you search for a ‘\n’ in the string. What happens if there isn’t a ‘\n’ in the string? What value is i?

I’m pretty sure the problem is that at some point or another, this style of code, is writing outside the allocated memory – since I don’t know exactly what your input is, I can’t say which of the several copies of this code is going wrong, but I’d bet that is what happens. That in turn means some data in the heap-structure itself is being corrupted, so at some point when malloc is called, it uses this bad data in the code.