Notes langage C

Voir :

Voir aussi :

#include <stdio.h>
#include <string.h>
#include <malloc.h>
 
main(int argc, char **argv)
{
    int i, size;
 
 
#define SEPARATEUR " "
 
    char *cmdline;
 
    for (i=1; i < argc; i++)
       size +=  strlen(SEPARATEUR) + strlen(argv[i]);
 
    cmdline = malloc(size);
 
    if (cmdline ) {
        memset(cmdline, 0, size);
        for (i=1; i < argc; i++) {
            strcat(cmdline, argv[i]);
            strcat(cmdline, SEPARATEUR);
        }
    }
 
    printf("-- %s --", cmdline);
 
    system(cmdline);
 
}

Surcharger un symbole

Voir : https://stackoverflow.com/questions/2146059/limiting-syscall-access-for-a-linux-application

Is the application linked statically?

If not, you may override some symbols, for example, let's redefine socket:

int socket(int domain, int type, int protocol) {

      write(1,"Error\n",6);
      return -1;

}

Then build a shared library:

gcc -fPIC -shared test.c -o libtest.so

Let's run:

nc -l -p 6000

Ok.

And now:

$ LD_PRELOAD=./libtest.so nc -l -p 6000 Error Can't get socket

What happens when you run with variable LD_PRELOAD=./libtest.so? It overrides with symbols defined in libtest.so over those defined in the C library.

Sécurité

$ man gets

...
(DEPRECATED)
Never use this function.

BUGS
       Never  use  gets().   Because  it is impossible to tell without knowing the data in advance how many characters gets() will read, and because gets() will continue to store characters past the end of the
       buffer, it is extremely dangerous to use.  It has been used to break computer security.  Use fgets() instead.

       For more information, see CWE-242 (aka "Use of Inherently Dangerous Function") at http://cwe.mitre.org/data/definitions/242.html
...