check_snprintf_overflow.c

   1 /*
   2  * Copyright (C) 2010 Dan Carpenter.
   3  *
   4  * This program is free software; you can redistribute it and/or
   5  * modify it under the terms of the GNU General Public License
   6  * as published by the Free Software Foundation; either version 2
   7  * of the License, or (at your option) any later version.
   8  *
   9  * This program is distributed in the hope that it will be useful,
  10  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12  * GNU General Public License for more details.
  13  *
  14  * You should have received a copy of the GNU General Public License
  15  * along with this program; if not, see http://www.gnu.org/copyleft/gpl.txt
  16  */
  17
  18 #include "smatch.h"
  19
  20 static void match_snprintf(const char *fn, struct expression *expr, void *unused)
  21 {
  22         struct expression *dest;
  23         struct expression *dest_size_expr;
  24         struct expression *format_string;
  25         struct expression *data;
  26         char *data_name = NULL;
  27         int dest_size;
  28         sval_t limit_size;
  29         char *format;
  30         int data_size;
  31
  32         dest = get_argument_from_call_expr(expr->args, 0);
  33         dest_size_expr = get_argument_from_call_expr(expr->args, 1);
  34         format_string = get_argument_from_call_expr(expr->args, 2);
  35         data = get_argument_from_call_expr(expr->args, 3);
  36
  37         dest_size = get_array_size_bytes(dest);
  38         if (!get_implied_value(dest_size_expr, &limit_size))
  39                 return;
  40         if (dest_size > 1 && dest_size < limit_size.value)
  41                 sm_error("snprintf() is printing too much %s vs %d",
  42                          sval_to_str(limit_size), dest_size);
  43         format = expr_to_var(format_string);
  44         if (!format)
  45                 return;
  46         if (strcmp(format, "\"%s\""))
  47                 goto free;
  48         data_name = expr_to_str(data);
  49         data_size = get_size_from_strlen(data);
  50         if (!data_size)
  51                 data_size = get_array_size_bytes(data);
  52         if (limit_size.value < data_size)
  53                 sm_error("snprintf() chops off the last chars of '%s': %d vs %s",
  54                        data_name, data_size, sval_to_str(limit_size));
  55 free:
  56         free_string(data_name);
  57         free_string(format);
  58 }
  59
  60 void check_snprintf_overflow(int id)
  61 {
  62         add_function_hook("snprintf", &match_snprintf, NULL);
  63 }