smatch_struct_assignment.c

   1 /*
   2  * Copyright (C) 2014 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 file started out by saying that if you have:
  20  *
  21  *      struct foo one, two;
  22  *      ...
  23  *      one = two;
  24  *
  25  * That's equivalent to saying:
  26  *
  27  *      one.x = two.x;
  28  *      one.y = two.y;
  29  *
  30  * Turning an assignment like that into a bunch of small fake assignments is
  31  * really useful.
  32  *
  33  * The call to memcpy(&one, &two, sizeof(foo)); is the same as "one = two;" so
  34  * we can re-use the code.  And we may as well use it for memset() too.
  35  * Assigning pointers is almost the same:
  36  *
  37  *      p1 = p2;
  38  *
  39  * Is the same as:
  40  *
  41  *      p1->x = p2->x;
  42  *      p1->y = p2->y;
  43  *
  44  * The problem is that you can go a bit crazy with pointers to pointers.
  45  *
  46  *      p1->x->y->z->one->two->three = p2->x->y->z->one->two->three;
  47  *
  48  * I don't have a proper solution for this problem right now.  I just copy one
  49  * level and don't nest.  It should handle limitted nesting but intelligently.
  50  *
  51  * The other thing is that you end up with a lot of garbage assignments where
  52  * we record "x could be anything. x->y could be anything. x->y->z->a->b->c
  53  * could *also* be anything!".  There should be a better way to filter this
  54  * useless information.
  55  *
  56  */
  57
  58 #include "scope.h"
  59 #include "smatch.h"
  60 #include "smatch_slist.h"
  61 #include "smatch_extra.h"
  62
  63 enum {
  64         COPY_NORMAL,
  65         COPY_MEMCPY,
  66         COPY_MEMSET,
  67 };
  68
  69 static struct symbol *get_struct_type(struct expression *expr)
  70 {
  71         struct symbol *type;
  72
  73         type = get_type(expr);
  74         if (!type)
  75                 return NULL;
  76         if (type->type == SYM_PTR)
  77                 type = get_real_base_type(type);
  78         if (type && type->type == SYM_STRUCT)
  79                 return type;
  80         return NULL;
  81 }
  82
  83 static struct expression *get_right_base_expr(struct symbol *left_type, struct expression *right)
  84 {
  85         struct symbol *struct_type;
  86
  87         if (!right)
  88                 return NULL;
  89
  90         struct_type = get_struct_type(right);
  91         if (!struct_type)
  92                 return NULL;
  93         if (struct_type != left_type)
  94                 return NULL;
  95
  96         if (right->type == EXPR_PREOP && right->op == '&')
  97                 right = strip_expr(right->unop);
  98
  99         if (right->type == EXPR_CALL)
 100                 return NULL;
 101
 102         if (is_pointer(right))
 103                 right = deref_expression(right);
 104
 105         return right;
 106 }
 107
 108 static struct expression *remove_addr(struct expression *expr)
 109 {
 110         struct symbol *type;
 111
 112         expr = strip_expr(expr);
 113
 114         if (expr->type == EXPR_PREOP && expr->op == '&')
 115                 return strip_expr(expr->unop);
 116         type = get_type(expr);
 117         if (!type || type->type != SYM_PTR)
 118                 return expr;
 119
 120         return deref_expression(expr);
 121 }
 122
 123 static struct expression *faked_expression;
 124 struct expression *get_faked_expression(void)
 125 {
 126         if (!__in_fake_assign)
 127                 return NULL;
 128         return faked_expression;
 129 }
 130
 131 static void split_fake_expr(struct expression *expr)
 132 {
 133         __in_fake_assign++;
 134         __split_expr(expr);
 135         __in_fake_assign--;
 136 }
 137
 138 static void set_inner_struct_members(int mode, struct expression *faked, struct expression *left, struct expression *right, struct symbol *member)
 139 {
 140         struct expression *left_member;
 141         struct expression *right_member = NULL;  /* silence GCC */
 142         struct expression *assign;
 143         struct symbol *base = get_real_base_type(member);
 144         struct symbol *tmp;
 145
 146         if (member->ident) {
 147                 left = member_expression(left, '.', member->ident);
 148                 if (mode != COPY_MEMSET && right)
 149                         right = member_expression(right, '.', member->ident);
 150         }
 151
 152         FOR_EACH_PTR(base->symbol_list, tmp) {
 153                 struct symbol *type;
 154
 155                 type = get_real_base_type(tmp);
 156                 if (!type)
 157                         continue;
 158
 159                 if (type->type == SYM_ARRAY)
 160                         continue;
 161                 if (type->type == SYM_UNION || type->type == SYM_STRUCT) {
 162                         set_inner_struct_members(mode, faked, left, right, tmp);
 163                         continue;
 164                 }
 165                 if (!tmp->ident)
 166                         continue;
 167
 168                 left_member = member_expression(left, '.', tmp->ident);
 169
 170                 switch (mode) {
 171                 case COPY_NORMAL:
 172                 case COPY_MEMCPY:
 173                         if (right)
 174                                 right_member = member_expression(right, '.', tmp->ident);
 175                         else
 176                                 right_member = unknown_value_expression(left_member);
 177                         break;
 178                 case COPY_MEMSET:
 179                         right_member = right;
 180                         break;
 181                 }
 182
 183                 assign = assign_expression(left_member, right_member);
 184                 split_fake_expr(assign);
 185         } END_FOR_EACH_PTR(tmp);
 186 }
 187
 188 static void __struct_members_copy(int mode, struct expression *faked,
 189                                   struct expression *left,
 190                                   struct expression *right)
 191 {
 192         struct symbol *struct_type, *tmp, *type;
 193         struct expression *left_member;
 194         struct expression *right_member;
 195         struct expression *assign;
 196         int op = '.';
 197
 198
 199         if (__in_fake_assign)
 200                 return;
 201         faked_expression = faked;
 202
 203         left = strip_expr(left);
 204         right = strip_expr(right);
 205
 206         struct_type = get_struct_type(left);
 207         if (!struct_type) {
 208                 /*
 209                  * This is not a struct assignment obviously.  But this is where
 210                  * memcpy() is handled so it feels like a good place to add this
 211                  * code.
 212                  */
 213
 214                 type = get_type(left);
 215                 if (!type || type->type != SYM_BASETYPE)
 216                         goto done;
 217
 218                 right = strip_expr(right);
 219                 if (right && right->type == EXPR_PREOP && right->op == '&')
 220                         right = remove_addr(right);
 221                 else
 222                         right = unknown_value_expression(left);
 223                 assign = assign_expression(left, right);
 224                 split_fake_expr(assign);
 225                 goto done;
 226         }
 227
 228         if (is_pointer(left)) {
 229                 left = deref_expression(left);
 230                 op = '*';
 231         }
 232         if (mode != COPY_MEMSET)
 233                 right = get_right_base_expr(struct_type, right);
 234
 235         FOR_EACH_PTR(struct_type->symbol_list, tmp) {
 236                 type = get_real_base_type(tmp);
 237                 if (!type)
 238                         continue;
 239                 if (type->type == SYM_ARRAY)
 240                         continue;
 241
 242                 if (type->type == SYM_UNION || type->type == SYM_STRUCT) {
 243                         set_inner_struct_members(mode, faked, left, right, tmp);
 244                         continue;
 245                 }
 246
 247                 if (!tmp->ident)
 248                         continue;
 249
 250                 left_member = member_expression(left, op, tmp->ident);
 251                 right_member = NULL;
 252
 253                 switch (mode) {
 254                 case COPY_NORMAL:
 255                 case COPY_MEMCPY:
 256                         if (right)
 257                                 right_member = member_expression(right, op, tmp->ident);
 258                         else
 259                                 right_member = unknown_value_expression(left_member);
 260                         break;
 261                 case COPY_MEMSET:
 262                         right_member = right;
 263                         break;
 264                 }
 265                 if (!right_member) {
 266                         sm_msg("internal.  No right member");
 267                         continue;
 268                 }
 269                 assign = assign_expression(left_member, right_member);
 270                 split_fake_expr(assign);
 271         } END_FOR_EACH_PTR(tmp);
 272
 273 done:
 274         faked_expression = NULL;
 275 }
 276
 277 static int returns_zeroed_mem(struct expression *expr)
 278 {
 279         char *fn;
 280
 281         if (expr->type != EXPR_CALL || expr->fn->type != EXPR_SYMBOL)
 282                 return 0;
 283         fn = expr_to_var(expr->fn);
 284         if (!fn)
 285                 return 0;
 286         if (strcmp(fn, "kcalloc") == 0)
 287                 return 1;
 288         if (option_project == PROJ_KERNEL && strstr(fn, "zalloc"))
 289                 return 1;
 290         return 0;
 291 }
 292
 293 void __fake_struct_member_assignments(struct expression *expr)
 294 {
 295         struct symbol *struct_type;
 296         struct symbol *left_type;
 297
 298         if (expr->op != '=')
 299                 return;
 300
 301         if (is_zero(expr->right))
 302                 return;
 303
 304         left_type = get_type(expr->left);
 305         if (left_type &&
 306             left_type->type != SYM_PTR &&
 307             left_type->type != SYM_STRUCT &&
 308             left_type != &ulong_ctype)
 309                 return;
 310
 311         struct_type = get_struct_type(expr->left);
 312         if (!struct_type)
 313                 return;
 314
 315         if (returns_zeroed_mem(expr->right))
 316                 __struct_members_copy(COPY_MEMSET, expr, expr->left, zero_expr());
 317         else
 318                 __struct_members_copy(COPY_NORMAL, expr, expr->left, expr->right);
 319 }
 320
 321 static void match_memset(const char *fn, struct expression *expr, void *_size_arg)
 322 {
 323         struct expression *buf;
 324         struct expression *val;
 325
 326         buf = get_argument_from_call_expr(expr->args, 0);
 327         val = get_argument_from_call_expr(expr->args, 1);
 328
 329         buf = strip_expr(buf);
 330         __struct_members_copy(COPY_MEMSET, expr, remove_addr(buf), val);
 331 }
 332
 333 static void match_memcpy(const char *fn, struct expression *expr, void *_arg)
 334 {
 335         struct expression *dest;
 336         struct expression *src;
 337
 338         dest = get_argument_from_call_expr(expr->args, 0);
 339         src = get_argument_from_call_expr(expr->args, 1);
 340
 341         __struct_members_copy(COPY_MEMCPY, expr, remove_addr(dest), remove_addr(src));
 342 }
 343
 344 static void match_memcpy_unknown(const char *fn, struct expression *expr, void *_arg)
 345 {
 346         struct expression *dest;
 347
 348         dest = get_argument_from_call_expr(expr->args, 0);
 349         __struct_members_copy(COPY_MEMCPY, expr, remove_addr(dest), NULL);
 350 }
 351
 352 static void match_sscanf(const char *fn, struct expression *expr, void *unused)
 353 {
 354         struct expression *arg;
 355         int i;
 356
 357         i = -1;
 358         FOR_EACH_PTR(expr->args, arg) {
 359                 if (++i < 2)
 360                         continue;
 361                 __struct_members_copy(COPY_MEMCPY, expr, remove_addr(arg), NULL);
 362         } END_FOR_EACH_PTR(arg);
 363 }
 364
 365 static void unop_expr(struct expression *expr)
 366 {
 367         if (expr->op != SPECIAL_INCREMENT &&
 368             expr->op != SPECIAL_DECREMENT)
 369                 return;
 370
 371         if (!is_pointer(expr))
 372                 return;
 373         __struct_members_copy(COPY_MEMCPY, expr, expr->unop, NULL);
 374 }
 375
 376 static void register_clears_param(void)
 377 {
 378         struct token *token;
 379         char name[256];
 380         const char *function;
 381         int param;
 382
 383         if (option_project == PROJ_NONE)
 384                 return;
 385
 386         snprintf(name, 256, "%s.clears_argument", option_project_str);
 387
 388         token = get_tokens_file(name);
 389         if (!token)
 390                 return;
 391         if (token_type(token) != TOKEN_STREAMBEGIN)
 392                 return;
 393         token = token->next;
 394         while (token_type(token) != TOKEN_STREAMEND) {
 395                 if (token_type(token) != TOKEN_IDENT)
 396                         return;
 397                 function = show_ident(token->ident);
 398                 token = token->next;
 399                 if (token_type(token) != TOKEN_NUMBER)
 400                         return;
 401                 param = atoi(token->number);
 402                 add_function_hook(function, &match_memcpy_unknown, INT_PTR(param));
 403                 token = token->next;
 404         }
 405         clear_token_alloc();
 406 }
 407
 408 static void db_param_cleared(struct expression *expr, int param, char *key, char *value)
 409 {
 410         struct expression *arg;
 411
 412         while (expr->type == EXPR_ASSIGNMENT)
 413                 expr = strip_expr(expr->right);
 414         if (expr->type != EXPR_CALL)
 415                 return;
 416
 417         /*
 418          * FIXME:  __struct_members_copy() requires an expression but
 419          * get_variable_from_key() returns a name/sym pair so that doesn't
 420          * work here.
 421          */
 422         if (strcmp(key, "$") != 0)
 423                 return;
 424
 425         arg = get_argument_from_call_expr(expr->args, param);
 426         if (!arg)
 427                 return;
 428
 429         if (strcmp(value, "0") == 0)
 430                 __struct_members_copy(COPY_MEMSET, expr, remove_addr(arg), zero_expr());
 431         else
 432                 __struct_members_copy(COPY_MEMCPY, expr, remove_addr(arg), NULL);
 433 }
 434
 435 void register_struct_assignment(int id)
 436 {
 437         add_function_hook("memset", &match_memset, NULL);
 438         add_function_hook("__memset", &match_memset, NULL);
 439
 440         add_function_hook("memcpy", &match_memcpy, INT_PTR(0));
 441         add_function_hook("memmove", &match_memcpy, INT_PTR(0));
 442         add_function_hook("__memcpy", &match_memcpy, INT_PTR(0));
 443         add_function_hook("__memmove", &match_memcpy, INT_PTR(0));
 444
 445         add_function_hook("sscanf", &match_sscanf, NULL);
 446
 447         add_hook(&unop_expr, OP_HOOK);
 448         register_clears_param();
 449         select_return_states_hook(PARAM_CLEARED, &db_param_cleared);
 450 }