contrib/pam_passwdqc/concat.c

   1 /*
   2  * concat() - allocate memory and safely concatenate strings in portable C
   3  * (and C++ if you like).
   4  *
   5  * This code deals gracefully with potential integer overflows (perhaps when
   6  * input strings are maliciously long), as well as with input strings changing
   7  * from under it (perhaps because of misbehavior of another thread).  It does
   8  * not depend on non-portable functions such as snprintf() and asprintf().
   9  *
  10  * Written by Solar Designer <solar at openwall.com> and placed in the
  11  * public domain.
  12  */
  13
  14 #include <string.h>
  15 #include <stdarg.h>
  16 #include <stdlib.h>
  17 #include <limits.h>
  18 #include "concat.h"
  19
  20 char *concat(const char *s1, ...)
  21 {
  22         va_list args;
  23         const char *s;
  24         char *p, *result;
  25         size_t l, m, n;
  26
  27         m = n = strlen(s1);
  28         va_start(args, s1);
  29         while ((s = va_arg(args, char *))) {
  30                 l = strlen(s);
  31                 if ((m += l) < l)
  32                         break;
  33         }
  34         va_end(args);
  35         if (s || m >= INT_MAX)
  36                 return NULL;
  37
  38         result = (char *)malloc(m + 1);
  39         if (!result)
  40                 return NULL;
  41
  42         memcpy(p = result, s1, n);
  43         p += n;
  44         va_start(args, s1);
  45         while ((s = va_arg(args, char *))) {
  46                 l = strlen(s);
  47                 if ((n += l) < l || n > m)
  48                         break;
  49                 memcpy(p, s, l);
  50                 p += l;
  51         }
  52         va_end(args);
  53         if (s || m != n || p != result + n) {
  54                 free(result);
  55                 return NULL;
  56         }
  57
  58         *p = 0;
  59         return result;
  60 }
  61
  62 #ifdef TEST
  63 #include <stdio.h>
  64
  65 int main(int argc, char **argv)
  66 {
  67         puts(concat(argv[0], argv[1], argv[2], argv[3], NULL));
  68         return 0;
  69 }
  70 #endif