operate with file and crash

I wrote a test file to grab all the TCP rule which has source port as "any" and destination port as "any", save them into a temp file.

the rule file example are as follow (the 4th parameter is source and the the 6th is destination port):

Code:

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alert tcp any any -> any any ( content:"Volume Serial Number"; sid:1292;)
alert tcp any 80 -> any any ( content:"Command completed"; sid:494;)
alert tcp any 80 -> any any ( content:"Bad command or filename"; sid:495;)
alert tcp any any -> any any ( content:"1 file|28|s|29| copied"; sid:497;)
alert tcp any 80 -> any any ( content:"Invalid URL"; sid:1200;)
alert tcp any 80 -> any any ( content:"Index of /cgi-bin/"; sid:1666;)
alert tcp any any -> any any ( content:"HTTP/1.1 403"; sid:1201;)
alert ip any any -> any any ( content:"uid=0|28|root|29|"; sid:498;)

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My code is:

Code:

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

#define MAXLINECHAR 2048

void DivideRule ();

FILE *ruleset, *ruletemp;

int main (void){

        ruleset = fopen ("ruleset.rules", "r");
        ruletemp = fopen ("ruletemp.rules", "w+");
   
        DivideRule ();

       
        fclose (ruletemp);       
        fclose (ruleset);
   
        return 0;
}


void DivideRule (){

        char F1[10], F2[10], F3[200], F4[10], F5[10], F6[10], F7[10];
       
        char *prerule, *temprule;
        char bufc;
       
           
        while ((fgetc (ruleset)) != EOF){ //get a character and see whether it is the end of the file
               
                fseek (ruleset, -1, 1); //go back to the start of the line
                prerule = (char *)malloc (MAXLINECHAR*sizeof(char)); //allocate a bunch of memory so as to store the rule
                fgets (prerule, MAXLINECHAR, ruleset); //grab a rule
                fseek (ruleset, -strlen(prerule), 1); //set the internal FILE pointer back to start of the line
               
                fscanf(ruleset, "%s %s %s %s %s %s %s", F1, F2, F3, F4, F5, F6, F7); //scan from the start to grab each parameter
                   
                if (F2[0] == 't' && F2[1] == 'c' && F2[2] == 'p'){ // if the protocol in the rule is TCP, go ahead
                    if (atoi (F4) == 0  && atoi (F7) == 0){  //port is 0 (source port is any/range and destination port is any/range), which means this rule should be insert into the Generic Set
                       
                                fprintf(ruletemp, "%s %s %s %s %s %s %s", F1, F2, F3, F4, F5, F6, F7);
                        temprule = (char *)malloc (MAXLINECHAR*sizeof(char)); //create a temp buffer to store the rest of characters in the line
                        fgets (temprule, MAXLINECHAR, ruleset);
                                fprintf (ruletemp, "%s", temprule);
                            free (temprule);
                        }
                }
                else{
                        temprule = (char *)malloc (MAXLINECHAR*sizeof(char));
                        fgets (temprule, MAXLINECHAR, ruleset);
                            free (temprule);
                }
       
                free (prerule);
    }
       
}

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When I compile the file, there is no error. However, when I run it in cygwin, it crashed. The error information are as follow:

"$ ./a.exe
10 [main] a 620_cygtls::handle_exceptions: Error while dumping state (probably corrupted stack)
Segmentation fault (core dumped)"

Please help me what's wrong with the code. Thanks a lot!

Why not add some error checking every time the file is read, for example whenever an fgets() or fscanf() operation is performed?

Code:

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                //scan from the start to grab each parameter
                if (fscanf(ruleset, "%s %s %s %s %s %s %s", F1, F2, F3, F4, F5, F6, F7) != 7)
                {
                        printf("Error reading from file.\n");
                }

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I got it. Add an "else" after "if (atoi (F4) == 0 && atoi (F7) == 0)" and works fine.

Thanks a lot!

Or even

Code:

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char buff[MAXLINECHAR];
while ( fgets( buff, sizeof buff, ruleset ) != NULL ) {
  if ( sscanf(ruleset, "%s %s %s %s %s %s %s", F1, F2, F3, F4, F5, F6, F7) == 7 ) {
    // do ya thang!
  } else {
    // bad format
  }
}

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A malloc/free call per line is a waste of effort, as is your apparent attempt to measure the length of each line only to do a max length line anyway with
prerule = (char *)malloc (MAXLINECHAR*sizeof(char));

Oh, and also see the FAQ on casting malloc in C.