check_string_len.c

   1 /*
   2  * Copyright (C) 2013 Oracle.
   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 /*
  19  * This tries to find buffer overflows in sprintf().
  20  * I'll freely admit that the code is sort of crap.
  21  * Also if it sees "sprintf("%2d\n", x)" then it assumes x is less than 99.
  22  * That might not be true so there maybe buffer overflows which are missed.
  23  *
  24  */
  25
  26 #include <ctype.h>
  27 #include "smatch.h"
  28
  29 static int my_id;
  30
  31 struct param_info {
  32         int buf_or_limit;
  33         int string;
  34 };
  35
  36 struct param_info zero_one = {0, 1};
  37
  38 static int handle_format(struct expression *call, char **pp, int *arg_nr)
  39 {
  40         struct expression *arg;
  41         char *p = *pp;
  42         int ret = 1;
  43         char buf[256];
  44         sval_t max;
  45
  46         p++;  /* we passed it with *p == '%' */
  47
  48         if (*p == '%') {
  49                 p++;
  50                 ret = 1;
  51                 goto out_no_arg;
  52         }
  53         if (*p == 'c') {
  54                 p++;
  55                 ret = 1;
  56                 goto out;
  57         }
  58
  59
  60         if (isdigit(*p) || *p == '.') {
  61                 unsigned long num;
  62
  63                 if (*p == '.')
  64                         p++;
  65
  66                 num = strtoul(p, &p, 10);
  67                 ret = num;
  68
  69                 while (*p == 'l')
  70                         p++;
  71                 p++; /* eat the 'd' char */
  72                 goto out;
  73         }
  74
  75         if (*p == 'l') {
  76                 p++;
  77                 if (*p == 'l')
  78                         p++;
  79         }
  80
  81         if (option_project == PROJ_KERNEL && *p == 'z')
  82                 p++;
  83
  84         if (option_project == PROJ_KERNEL && *p == 'p') {
  85                 if (*(p + 1) == 'I' || *(p + 1) == 'i') {
  86                         char *eye;
  87
  88                         eye = p + 1;
  89                         p += 2;
  90                         if (*p == 'h' || *p == 'n' || *p == 'b' || *p == 'l')
  91                                 p++;
  92                         if (*p == '4') {
  93                                 p++;
  94                                 ret = 15;
  95                                 goto out;
  96                         }
  97                         if (*p == '6') {
  98                                 p++;
  99                                 if (*p == 'c')
 100                                         p++;
 101                                 if (*eye == 'I')
 102                                         ret = 39;
 103                                 if (*eye == 'i')
 104                                         ret = 32;
 105                                 goto out;
 106                         }
 107                 }
 108                 if (*(p + 1) == 'M') {
 109                         p += 2;
 110                         if (*p == 'R' || *p == 'F')
 111                                 p++;
 112                         ret = 17;
 113                         goto out;
 114                 }
 115                 if (*(p + 1) == 'm') {
 116                         p += 2;
 117                         if (*p == 'R')
 118                                 p++;
 119                         ret = 12;
 120                         goto out;
 121                 }
 122         }
 123
 124         arg = get_argument_from_call_expr(call->args, *arg_nr);
 125         if (!arg)
 126                 goto out;
 127
 128         if (*p == 's') {
 129                 ret = get_array_size_bytes(arg);
 130                 if (ret < 0)
 131                         ret = 1;
 132                 /* we don't print the NUL here */
 133                 ret--;
 134                 p++;
 135                 goto out;
 136         }
 137
 138         if (*p != 'd' && *p != 'i' && *p != 'x' && *p != 'X' && *p != 'u' && *p != 'p') {
 139                 ret = 1;
 140                 p++;
 141                 goto out;
 142         }
 143
 144         get_absolute_max(arg, &max);
 145
 146         if (*p == 'x' || *p == 'X' || *p == 'p') {
 147                 ret = snprintf(buf, sizeof(buf), "%llx", max.uvalue);
 148         } else if (*p == 'u') {
 149                 ret = snprintf(buf, sizeof(buf), "%llu", max.uvalue);
 150         } else if (!expr_unsigned(arg)) {
 151                 sval_t min;
 152                 int tmp;
 153
 154                 ret = snprintf(buf, sizeof(buf), "%lld", max.value);
 155                 get_absolute_min(arg, &min);
 156                 tmp = snprintf(buf, sizeof(buf), "%lld", min.value);
 157                 if (tmp > ret)
 158                         ret = tmp;
 159         } else {
 160                 ret = snprintf(buf, sizeof(buf), "%lld", max.value);
 161         }
 162         p++;
 163
 164 out:
 165         (*arg_nr)++;
 166 out_no_arg:
 167         *pp = p;
 168         return ret;
 169 }
 170
 171 int get_formatted_string_size(struct expression *call, int arg)
 172 {
 173         struct expression *expr;
 174         char *p;
 175         int count;
 176
 177         expr = get_argument_from_call_expr(call->args, arg);
 178         if (!expr || expr->type != EXPR_STRING)
 179                 return -1;
 180
 181         arg++;
 182         count = 0;
 183         p = expr->string->data;
 184         while (*p) {
 185
 186                 if (*p == '%') {
 187                         count += handle_format(call, &p, &arg);
 188                 } else if (*p == '\\') {
 189                         p++;
 190                 }else {
 191                         p++;
 192                         count++;
 193                 }
 194         }
 195
 196         count++; /* count the NUL terminator */
 197         return count;
 198 }
 199
 200 static void match_not_limited(const char *fn, struct expression *call, void *info)
 201 {
 202         struct param_info *params = info;
 203         struct expression *dest;
 204         struct expression *arg;
 205         int buf_size, size;
 206         int user = 0;
 207         int i;
 208         int offset = 0;
 209
 210         dest = get_argument_from_call_expr(call->args, params->buf_or_limit);
 211         dest = strip_expr(dest);
 212         if (dest->type == EXPR_BINOP && dest->op == '+') {
 213                 sval_t max;
 214
 215                 if (get_hard_max(dest->right, &max))
 216                         offset = max.value;
 217                 dest = dest->left;
 218         }
 219
 220
 221         buf_size = get_array_size_bytes(dest);
 222         if (buf_size <= 0)
 223                 return;
 224
 225         size = get_formatted_string_size(call, params->string);
 226         if (size <= 0)
 227                 return;
 228         if (size < offset)
 229                 size -= offset;
 230         if (size <= buf_size)
 231                 return;
 232
 233         i = 0;
 234         FOR_EACH_PTR(call->args, arg) {
 235                 if (i++ <= params->string)
 236                         continue;
 237                 if (is_user_data(arg))
 238                         user = 1;
 239         } END_FOR_EACH_PTR(arg);
 240
 241         sm_msg("error: format string overflow. buf_size: %d length: %d%s",
 242                buf_size, size, user ? " [user data]": "");
 243 }
 244
 245 void check_string_len(int id)
 246 {
 247         my_id = id;
 248         add_function_hook("sprintf", &match_not_limited, &zero_one);
 249 }
 250