smatch_points_to_user_data.c

   1 /*
   2  * Copyright (C) 2020 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  * The problem here is that we can have:
  20  *
  21  * p = skb->data;
  22  *
  23  * In the olden days we would just set "*p = 0-255" which meant that it pointed
  24  * to user data.  But then if we say "if (*p == 11) {" that means that "*p" is
  25  * not user data any more, so then "*(p + 1)" is marked as not user data but it
  26  * is.
  27  *
  28  * So now we've separated out the stuff that points to a user_buf from the other
  29  * user data.
  30  *
  31  * There is a further complication because what if "p" points to a struct?  In
  32  * that case all the struct members are handled by smatch_kernel_user_data.c
  33  * but we still need to keep in mind that "*(p + 1)" is user data.  I'm not
  34  * totally 100% sure how this will work.
  35  *
  36  * Generally a user pointer should be a void pointer, or an array etc.  But if
  37  * it points to a struct that can only be used for pointer math.
  38  *
  39  */
  40
  41 #include "smatch.h"
  42 #include "smatch_slist.h"
  43 #include "smatch_extra.h"
  44
  45 static int my_id;
  46 STATE(user_data);
  47
  48 static const char *returns_pointer_to_user_data[] = {
  49         "nlmsg_data", "nla_data", "memdup_user", "kmap_atomic", "skb_network_header",
  50         "cfg80211_find_elem_match", "ieee80211_bss_get_elem", "cfg80211_find_elem",
  51         "ieee80211_bss_get_ie",
  52 };
  53
  54 bool is_skb_data(struct expression *expr)
  55 {
  56         struct symbol *sym;
  57
  58         expr = strip_expr(expr);
  59         if (!expr)
  60                 return false;
  61
  62         expr = strip_expr(expr);
  63         if (!expr)
  64                 return false;
  65         if (expr->type != EXPR_DEREF)
  66                 return false;
  67
  68         if (!expr->member)
  69                 return false;
  70         if (strcmp(expr->member->name, "data") != 0)
  71                 return false;
  72
  73         sym = get_type(expr->deref);
  74         if (!sym)
  75                 return false;
  76         if (sym->type == SYM_PTR)
  77                 sym = get_real_base_type(sym);
  78         if (!sym || sym->type != SYM_STRUCT || !sym->ident)
  79                 return false;
  80         if (strcmp(sym->ident->name, "sk_buff") != 0)
  81                 return false;
  82
  83         return true;
  84 }
  85
  86 bool is_user_data_fn(struct symbol *fn)
  87 {
  88         int i;
  89
  90         if (!fn || !fn->ident)
  91                 return false;
  92
  93         for (i = 0; i < ARRAY_SIZE(returns_pointer_to_user_data); i++) {
  94                 if (strcmp(fn->ident->name, returns_pointer_to_user_data[i]) == 0) {
  95 //                      func_gets_user_data = true;
  96                         return true;
  97                 }
  98         }
  99         return false;
 100 }
 101
 102 static bool is_points_to_user_data_fn(struct expression *expr)
 103 {
 104         expr = strip_expr(expr);
 105         if (!expr || expr->type != EXPR_CALL || expr->fn->type != EXPR_SYMBOL ||
 106             !expr->fn->symbol)
 107                 return false;
 108         return is_user_data_fn(expr->fn->symbol);
 109 }
 110
 111 static bool is_array_of_user_data(struct expression *expr)
 112 {
 113         struct expression *deref;
 114         struct symbol *type;
 115
 116         if (expr->type == EXPR_PREOP && expr->op == '&') {
 117                 expr = strip_expr(expr->unop);
 118                 if (expr->type == EXPR_PREOP && expr->op == '*')
 119                         expr = strip_expr(expr->unop);
 120         }
 121
 122         /* This is for array elements &foo->data[4] */
 123         if (expr->type == EXPR_BINOP && expr->op == '+') {
 124                 if (points_to_user_data(expr->left))
 125                         return true;
 126                 if (points_to_user_data(expr->right))
 127                         return true;
 128         }
 129
 130         /* This is for if you have: foo = skb->data; frob(foo->array); */
 131         type = get_type(expr);
 132         if (!type || type->type != SYM_ARRAY)
 133                 return false;
 134
 135         if (expr->type != EXPR_DEREF)
 136                 return false;
 137         deref = strip_expr(expr->deref);
 138         if (deref->type != EXPR_PREOP || deref->op != '*')
 139                 return false;
 140         deref = strip_expr(deref->unop);
 141         return points_to_user_data(deref);
 142 }
 143
 144 bool points_to_user_data(struct expression *expr)
 145 {
 146         struct sm_state *sm;
 147
 148         expr = strip_expr(expr);
 149         if (!expr)
 150                 return false;
 151
 152         if (is_fake_call(expr))
 153                 return false;
 154
 155         if (expr->type == EXPR_ASSIGNMENT)
 156                 return points_to_user_data(expr->left);
 157
 158         if (is_array_of_user_data(expr))
 159                 return true;
 160
 161         if (expr->type == EXPR_BINOP && expr->op == '+')
 162                 expr = strip_expr(expr->left);
 163
 164         if (is_skb_data(expr))
 165                 return true;
 166
 167         if (is_points_to_user_data_fn(expr))
 168                 return true;
 169
 170         sm = get_sm_state_expr(my_id, expr);
 171         if (sm && slist_has_state(sm->possible, &user_data))
 172                 return true;
 173         return false;
 174 }
 175
 176 void set_points_to_user_data(struct expression *expr)
 177 {
 178         set_state_expr(my_id, expr, &user_data);
 179 }
 180
 181 static void match_assign(struct expression *expr)
 182 {
 183         if (is_fake_call(expr->right))
 184                 return;
 185
 186         if (!is_ptr_type(get_type(expr->left)))
 187                 return;
 188
 189         if (points_to_user_data(expr->right)) {
 190                 set_points_to_user_data(expr->left);
 191                 return;
 192         }
 193
 194         if (get_state_expr(my_id, expr->left))
 195                 set_state_expr(my_id, expr->left, &undefined);
 196 }
 197
 198 static void match_memcpy(const char *fn, struct expression *expr, void *_unused)
 199 {
 200         struct expression *dest, *src;
 201
 202         dest = get_argument_from_call_expr(expr->args, 0);
 203         src = get_argument_from_call_expr(expr->args, 1);
 204
 205         if (points_to_user_data(src)) {
 206                 set_points_to_user_data(dest);
 207                 return;
 208         }
 209
 210         if (get_state_expr(my_id, dest))
 211                 set_state_expr(my_id, dest, &undefined);
 212 }
 213
 214 static void match_user_copy(const char *fn, struct expression *expr, void *_unused)
 215 {
 216         struct expression *dest, *size;
 217         sval_t sval;
 218
 219         dest = get_argument_from_call_expr(expr->args, 0);
 220         dest = strip_expr(dest);
 221         if (!dest)
 222                 return;
 223
 224         size = get_argument_from_call_expr(expr->args, 2);
 225         if (get_implied_value(size, &sval))
 226                 return;
 227
 228         set_state_expr(my_id, dest, &user_data);
 229 }
 230
 231 static void return_info_callback(int return_id, char *return_ranges,
 232                                  struct expression *returned_expr,
 233                                  int param,
 234                                  const char *printed_name,
 235                                  struct sm_state *sm)
 236 {
 237         int type = USER_PTR_SET;
 238
 239         if (!slist_has_state(sm->possible, &user_data))
 240                 return;
 241
 242         if (param >= 0) {
 243                 if (get_state_stree(get_start_states(), my_id, sm->name, sm->sym))
 244                         return;
 245         } else {
 246                 if (!param_was_set_var_sym(sm->name, sm->sym))
 247                         type = USER_PTR;
 248         }
 249         if (parent_is_gone_var_sym(sm->name, sm->sym))
 250                 return;
 251
 252         sql_insert_return_states(return_id, return_ranges, type,
 253                                  param, printed_name, "");
 254 }
 255
 256 static void returns_user_ptr_helper(struct expression *expr, int param, char *key, char *value, bool set)
 257 {
 258         struct expression *arg;
 259         struct expression *call;
 260         char *name;
 261         struct symbol *sym;
 262
 263         call = expr;
 264         while (call->type == EXPR_ASSIGNMENT)
 265                 call = strip_expr(call->right);
 266         if (call->type != EXPR_CALL)
 267                 return;
 268
 269         if (!set && !we_pass_user_data(call))
 270                 return;
 271
 272         if (param == -1) {
 273                 if (expr->type != EXPR_ASSIGNMENT) {
 274                         /* Nothing to do.  Fake assignments should handle it */
 275                         return;
 276                 }
 277                 arg = expr->left;
 278                 goto set_user;
 279         }
 280
 281         arg = get_argument_from_call_expr(call->args, param);
 282         if (!arg)
 283                 return;
 284 set_user:
 285         name = get_variable_from_key(arg, key, &sym);
 286         if (!name || !sym)
 287                 goto free;
 288         set_state(my_id, name, sym, &user_data);
 289 free:
 290         free_string(name);
 291 }
 292
 293 static void returns_user_ptr(struct expression *expr, int param, char *key, char *value)
 294 {
 295         returns_user_ptr_helper(expr, param, key, value, false);
 296 }
 297
 298 static void returns_user_ptr_set(struct expression *expr, int param, char *key, char *value)
 299 {
 300         returns_user_ptr_helper(expr, param, key, value, true);
 301 }
 302
 303 static void set_param_user_ptr(const char *name, struct symbol *sym, char *key, char *value)
 304 {
 305         struct expression *expr;
 306         char *fullname;
 307
 308         expr = symbol_expression(sym);
 309         fullname = get_variable_from_key(expr, key, NULL);
 310         if (!fullname)
 311                 return;
 312         set_state(my_id, fullname, sym, &user_data);
 313 }
 314
 315 static void caller_info_callback(struct expression *call, int param, char *printed_name, struct sm_state *sm)
 316 {
 317         if (!slist_has_state(sm->possible, &user_data))
 318                 return;
 319         sql_insert_caller_info(call, USER_PTR, param, printed_name, "");
 320 }
 321
 322 void register_points_to_user_data(int id)
 323 {
 324         my_id = id;
 325
 326         if (option_project != PROJ_KERNEL)
 327                 return;
 328
 329         add_hook(&match_assign, ASSIGNMENT_HOOK);
 330
 331         add_function_hook("copy_from_user", &match_user_copy, NULL);
 332         add_function_hook("memcpy_from_msg", &match_user_copy, NULL);
 333         add_function_hook("__copy_from_user", &match_user_copy, NULL);
 334
 335         add_function_hook("memcpy", &match_memcpy, NULL);
 336         add_function_hook("__memcpy", &match_memcpy, NULL);
 337
 338         add_caller_info_callback(my_id, caller_info_callback);
 339         add_return_info_callback(my_id, return_info_callback);
 340
 341         select_caller_info_hook(set_param_user_ptr, USER_PTR);
 342         select_return_states_hook(USER_PTR, &returns_user_ptr);
 343         select_return_states_hook(USER_PTR_SET, &returns_user_ptr_set);
 344 }