truncationbug.c

#include <stdlib.h>
#include <stdio.h>
#include <limits.h>
#include <fcntl.h>
#include <errno.h>

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

    //##################
    //##  Parse Arguments (primitive)
    //####################
    ulong write_iterations = 0;
    ulong iterations = ULONG_MAX;

    if ( argc < 4) {
        printf("%s tempFile realFile sampleFile\n", argv[0]);
        exit(7);
    }
    char * tempFile = argv[1];
    char * realFile = argv[2];
    char * sampleFile = argv[3];

    if ( argc > 4) {
      char *pEnd;
      write_iterations = strtoul(argv[4],&pEnd,10);
      if ( argc > 5) {
          iterations = strtoul(argv[5], &pEnd, 10);
      }
    }

    //########################
    //##  Read Sample File
    //#########################
    char * buffer = 0;
    long length;
    FILE * f = fopen (sampleFile, "rb");

    if (!f) {
        printf("Unable to open sample file (%s)", sampleFile);
        exit(9);
    }
        
    // Get the size of the sample file
    fseek (f, 0, SEEK_END);
    length = ftell (f);
    fseek (f, 0, SEEK_SET);
    
    buffer = malloc (length);
    
    if(!buffer) {
        printf("Unable to allocate buffer for sample file\n");
        exit(8);
    }

    fread (buffer, 1, length, f);
    fclose (f);

    // If the realFile of the tempFile exist, remove them
    // We want a clean test environment
    remove(tempFile);
    remove(realFile);

    // We're about to hit the real stuff
    // Loop over this a bunch of times to increase the chances we trigger the issue
    ulong i = 0;
    for ( i = 0 ; i < iterations ; i++) { 

        // See if we should write out how many iterations we've performed
        if ( write_iterations != 0 )
          if ( i % write_iterations == 0) {
            printf("\rIteration %10lu", i);
            fflush(stdout);
          }

        /////////////////////////////////////////////////////
        ///  The Main Event
        //////////////////////////////////////////////////////

        // Open file  O_RDWR|O_CREAT|O_EXCL|O_TRUNC 0600
       int fp = open(tempFile, O_RDWR|O_CREAT|O_EXCL|O_TRUNC, S_IRUSR | S_IWUSR);
        
        // Write 
        write( fp,  buffer, length  );

        // Close
        close(fp);
        
        // Link Actual file to temp file
        int l = link(tempFile, realFile);
        if( l != 0) {
            printf("Huston, we have a problem linking the files (%s) -> (%s)", tempFile, realFile);
            exit(6);
        }

        // Unlink Temp File
        int r = remove(tempFile);
        if(r != 0) {
            printf("Huston, we have a problem (removing tempFile)\n");
            exit(5);
        }

        // Stat file and ensure it is the expected size
        struct stat st;
        if(stat(realFile, &st) != 0) {
            printf("File Error Message = %s\n", strerror(errno));
            exit(3);
        } else if (st.st_size != length) {
            exit(4);
        }
        // Cleanup
        remove(realFile);
    }
}