Jorge Lucangeli Obes | a6b034d | 2012-08-07 15:29:20 -0700 | [diff] [blame] | 1 | /* Copyright (c) 2012 The Chromium OS Authors. All rights reserved. |
Jorge Lucangeli Obes | fc8ab53 | 2012-03-20 10:14:31 -0700 | [diff] [blame] | 2 | * Use of this source code is governed by a BSD-style license that can be |
| 3 | * found in the LICENSE file. |
Jorge Lucangeli Obes | fc8ab53 | 2012-03-20 10:14:31 -0700 | [diff] [blame] | 4 | */ |
| 5 | |
Jorge Lucangeli Obes | fc8ab53 | 2012-03-20 10:14:31 -0700 | [diff] [blame] | 6 | #include <stdio.h> |
| 7 | #include <stdlib.h> |
| 8 | #include <string.h> |
Jorge Lucangeli Obes | fc8ab53 | 2012-03-20 10:14:31 -0700 | [diff] [blame] | 9 | |
| 10 | #include "syscall_filter.h" |
| 11 | |
Jorge Lucangeli Obes | a6b034d | 2012-08-07 15:29:20 -0700 | [diff] [blame] | 12 | #include "util.h" |
Jorge Lucangeli Obes | d446726 | 2012-03-23 16:19:59 -0700 | [diff] [blame] | 13 | |
Jorge Lucangeli Obes | 3dc257c | 2016-11-01 12:25:04 -0400 | [diff] [blame] | 14 | /* clang-format off */ |
Jorge Lucangeli Obes | 565e978 | 2016-08-05 11:03:19 -0400 | [diff] [blame] | 15 | #define MAX_LINE_LENGTH 1024 |
Jorge Lucangeli Obes | bda833c | 2012-07-31 16:25:56 -0700 | [diff] [blame] | 16 | #define MAX_POLICY_LINE_LENGTH 1024 |
| 17 | |
Jorge Lucangeli Obes | a6b034d | 2012-08-07 15:29:20 -0700 | [diff] [blame] | 18 | #define ONE_INSTR 1 |
| 19 | #define TWO_INSTRS 2 |
Jorge Lucangeli Obes | 3dc257c | 2016-11-01 12:25:04 -0400 | [diff] [blame] | 20 | /* clang-format on */ |
Jorge Lucangeli Obes | d446726 | 2012-03-23 16:19:59 -0700 | [diff] [blame] | 21 | |
Jorge Lucangeli Obes | 7b2e29c | 2016-08-04 12:21:03 -0400 | [diff] [blame] | 22 | int seccomp_can_softfail() |
| 23 | { |
Jorge Lucangeli Obes | 565e978 | 2016-08-05 11:03:19 -0400 | [diff] [blame] | 24 | #if defined(USE_SECCOMP_SOFTFAIL) |
Jeff Vander Stoep | 1022fc3 | 2016-08-28 12:24:55 -0700 | [diff] [blame] | 25 | return 1; |
Jorge Lucangeli Obes | 7b2e29c | 2016-08-04 12:21:03 -0400 | [diff] [blame] | 26 | #endif |
| 27 | return 0; |
| 28 | } |
| 29 | |
Jorge Lucangeli Obes | fc8ab53 | 2012-03-20 10:14:31 -0700 | [diff] [blame] | 30 | int str_to_op(const char *op_str) |
| 31 | { |
| 32 | if (!strcmp(op_str, "==")) { |
| 33 | return EQ; |
| 34 | } else if (!strcmp(op_str, "!=")) { |
| 35 | return NE; |
Jorge Lucangeli Obes | 66cfc14 | 2012-11-30 15:42:52 -0800 | [diff] [blame] | 36 | } else if (!strcmp(op_str, "&")) { |
| 37 | return SET; |
Jorge Lucangeli Obes | fd6f8e3 | 2016-10-12 11:19:28 -0400 | [diff] [blame] | 38 | } else if (!strcmp(op_str, "in")) { |
| 39 | return IN; |
Jorge Lucangeli Obes | fc8ab53 | 2012-03-20 10:14:31 -0700 | [diff] [blame] | 40 | } else { |
| 41 | return 0; |
| 42 | } |
| 43 | } |
| 44 | |
Jorge Lucangeli Obes | fc8ab53 | 2012-03-20 10:14:31 -0700 | [diff] [blame] | 45 | struct sock_filter *new_instr_buf(size_t count) |
| 46 | { |
| 47 | struct sock_filter *buf = calloc(count, sizeof(struct sock_filter)); |
| 48 | if (!buf) |
Jorge Lucangeli Obes | 224e427 | 2012-08-02 14:31:39 -0700 | [diff] [blame] | 49 | die("could not allocate BPF instruction buffer"); |
Jorge Lucangeli Obes | fc8ab53 | 2012-03-20 10:14:31 -0700 | [diff] [blame] | 50 | |
| 51 | return buf; |
| 52 | } |
| 53 | |
Jorge Lucangeli Obes | d96baf4 | 2013-03-26 15:11:30 -0700 | [diff] [blame] | 54 | struct filter_block *new_filter_block() |
| 55 | { |
| 56 | struct filter_block *block = calloc(1, sizeof(struct filter_block)); |
| 57 | if (!block) |
| 58 | die("could not allocate BPF filter block"); |
| 59 | |
| 60 | block->instrs = NULL; |
| 61 | block->last = block->next = NULL; |
| 62 | |
| 63 | return block; |
| 64 | } |
| 65 | |
Jorge Lucangeli Obes | 565e978 | 2016-08-05 11:03:19 -0400 | [diff] [blame] | 66 | void append_filter_block(struct filter_block *head, struct sock_filter *instrs, |
| 67 | size_t len) |
Jorge Lucangeli Obes | fc8ab53 | 2012-03-20 10:14:31 -0700 | [diff] [blame] | 68 | { |
| 69 | struct filter_block *new_last; |
| 70 | |
| 71 | /* |
| 72 | * If |head| has no filter assigned yet, |
| 73 | * we don't create a new node. |
| 74 | */ |
| 75 | if (head->instrs == NULL) { |
| 76 | new_last = head; |
| 77 | } else { |
Jorge Lucangeli Obes | d96baf4 | 2013-03-26 15:11:30 -0700 | [diff] [blame] | 78 | new_last = new_filter_block(); |
Jorge Lucangeli Obes | fc8ab53 | 2012-03-20 10:14:31 -0700 | [diff] [blame] | 79 | if (head->next != NULL) { |
| 80 | head->last->next = new_last; |
| 81 | head->last = new_last; |
| 82 | } else { |
| 83 | head->last = head->next = new_last; |
| 84 | } |
| 85 | head->total_len += len; |
| 86 | } |
| 87 | |
| 88 | new_last->instrs = instrs; |
| 89 | new_last->total_len = new_last->len = len; |
| 90 | new_last->last = new_last->next = NULL; |
| 91 | } |
| 92 | |
Jorge Lucangeli Obes | d446726 | 2012-03-23 16:19:59 -0700 | [diff] [blame] | 93 | void extend_filter_block_list(struct filter_block *list, |
Jorge Lucangeli Obes | 565e978 | 2016-08-05 11:03:19 -0400 | [diff] [blame] | 94 | struct filter_block *another) |
Jorge Lucangeli Obes | d446726 | 2012-03-23 16:19:59 -0700 | [diff] [blame] | 95 | { |
| 96 | if (list->last != NULL) { |
| 97 | list->last->next = another; |
| 98 | list->last = another->last; |
| 99 | } else { |
| 100 | list->next = another; |
| 101 | list->last = another->last; |
| 102 | } |
| 103 | list->total_len += another->total_len; |
| 104 | } |
| 105 | |
Jorge Lucangeli Obes | fc8ab53 | 2012-03-20 10:14:31 -0700 | [diff] [blame] | 106 | void append_ret_kill(struct filter_block *head) |
| 107 | { |
| 108 | struct sock_filter *filter = new_instr_buf(ONE_INSTR); |
| 109 | set_bpf_ret_kill(filter); |
| 110 | append_filter_block(head, filter, ONE_INSTR); |
| 111 | } |
| 112 | |
Jorge Lucangeli Obes | bda833c | 2012-07-31 16:25:56 -0700 | [diff] [blame] | 113 | void append_ret_trap(struct filter_block *head) |
| 114 | { |
| 115 | struct sock_filter *filter = new_instr_buf(ONE_INSTR); |
| 116 | set_bpf_ret_trap(filter); |
| 117 | append_filter_block(head, filter, ONE_INSTR); |
| 118 | } |
| 119 | |
Jorge Lucangeli Obes | fc8ab53 | 2012-03-20 10:14:31 -0700 | [diff] [blame] | 120 | void append_ret_errno(struct filter_block *head, int errno_val) |
| 121 | { |
| 122 | struct sock_filter *filter = new_instr_buf(ONE_INSTR); |
| 123 | set_bpf_ret_errno(filter, errno_val); |
| 124 | append_filter_block(head, filter, ONE_INSTR); |
| 125 | } |
| 126 | |
Jorge Lucangeli Obes | c8b21e1 | 2014-06-13 14:26:16 -0700 | [diff] [blame] | 127 | void append_allow_syscall(struct filter_block *head, int nr) |
| 128 | { |
Jorge Lucangeli Obes | bda833c | 2012-07-31 16:25:56 -0700 | [diff] [blame] | 129 | struct sock_filter *filter = new_instr_buf(ALLOW_SYSCALL_LEN); |
| 130 | size_t len = bpf_allow_syscall(filter, nr); |
| 131 | if (len != ALLOW_SYSCALL_LEN) |
| 132 | die("error building syscall number comparison"); |
| 133 | |
| 134 | append_filter_block(head, filter, len); |
| 135 | } |
| 136 | |
Jorge Lucangeli Obes | 713f6fb | 2016-10-03 13:03:25 -0400 | [diff] [blame] | 137 | void allow_logging_syscalls(struct filter_block *head) |
Jorge Lucangeli Obes | bda833c | 2012-07-31 16:25:56 -0700 | [diff] [blame] | 138 | { |
| 139 | unsigned int i; |
Kees Cook | 03b2af2 | 2014-12-18 17:11:13 -0800 | [diff] [blame] | 140 | for (i = 0; i < log_syscalls_len; i++) { |
| 141 | warn("allowing syscall: %s", log_syscalls[i]); |
Jorge Lucangeli Obes | bda833c | 2012-07-31 16:25:56 -0700 | [diff] [blame] | 142 | append_allow_syscall(head, lookup_syscall(log_syscalls[i])); |
Kees Cook | 03b2af2 | 2014-12-18 17:11:13 -0800 | [diff] [blame] | 143 | } |
Jorge Lucangeli Obes | bda833c | 2012-07-31 16:25:56 -0700 | [diff] [blame] | 144 | } |
| 145 | |
Jorge Lucangeli Obes | fc8ab53 | 2012-03-20 10:14:31 -0700 | [diff] [blame] | 146 | unsigned int get_label_id(struct bpf_labels *labels, const char *label_str) |
| 147 | { |
| 148 | int label_id = bpf_label_id(labels, label_str); |
| 149 | if (label_id < 0) |
Jorge Lucangeli Obes | 224e427 | 2012-08-02 14:31:39 -0700 | [diff] [blame] | 150 | die("could not allocate BPF label string"); |
Jorge Lucangeli Obes | fc8ab53 | 2012-03-20 10:14:31 -0700 | [diff] [blame] | 151 | return label_id; |
| 152 | } |
| 153 | |
| 154 | unsigned int group_end_lbl(struct bpf_labels *labels, int nr, int idx) |
| 155 | { |
| 156 | char lbl_str[MAX_BPF_LABEL_LEN]; |
| 157 | snprintf(lbl_str, MAX_BPF_LABEL_LEN, "%d_%d_end", nr, idx); |
| 158 | return get_label_id(labels, lbl_str); |
| 159 | } |
| 160 | |
| 161 | unsigned int success_lbl(struct bpf_labels *labels, int nr) |
| 162 | { |
| 163 | char lbl_str[MAX_BPF_LABEL_LEN]; |
| 164 | snprintf(lbl_str, MAX_BPF_LABEL_LEN, "%d_success", nr); |
| 165 | return get_label_id(labels, lbl_str); |
| 166 | } |
| 167 | |
Jorge Lucangeli Obes | 66cfc14 | 2012-11-30 15:42:52 -0800 | [diff] [blame] | 168 | int compile_atom(struct filter_block *head, char *atom, |
Jorge Lucangeli Obes | 1a122b8 | 2016-11-01 11:59:33 -0400 | [diff] [blame^] | 169 | struct bpf_labels *labels, int nr, int grp_idx) |
Jorge Lucangeli Obes | 66cfc14 | 2012-11-30 15:42:52 -0800 | [diff] [blame] | 170 | { |
| 171 | /* Splits the atom. */ |
| 172 | char *atom_ptr; |
| 173 | char *argidx_str = strtok_r(atom, " ", &atom_ptr); |
Jorge Lucangeli Obes | 1a122b8 | 2016-11-01 11:59:33 -0400 | [diff] [blame^] | 174 | if (argidx_str == NULL) { |
| 175 | warn("empty atom"); |
| 176 | return -1; |
| 177 | } |
| 178 | |
Jorge Lucangeli Obes | 66cfc14 | 2012-11-30 15:42:52 -0800 | [diff] [blame] | 179 | char *operator_str = strtok_r(NULL, " ", &atom_ptr); |
Jorge Lucangeli Obes | 1a122b8 | 2016-11-01 11:59:33 -0400 | [diff] [blame^] | 180 | if (operator_str == NULL) { |
| 181 | warn("invalid atom '%s'", argidx_str); |
| 182 | return -1; |
| 183 | } |
| 184 | |
Jorge Lucangeli Obes | 66cfc14 | 2012-11-30 15:42:52 -0800 | [diff] [blame] | 185 | char *constant_str = strtok_r(NULL, " ", &atom_ptr); |
Jorge Lucangeli Obes | 1a122b8 | 2016-11-01 11:59:33 -0400 | [diff] [blame^] | 186 | if (constant_str == NULL) { |
| 187 | warn("invalid atom '%s %s'", argidx_str, operator_str); |
Jorge Lucangeli Obes | 66cfc14 | 2012-11-30 15:42:52 -0800 | [diff] [blame] | 188 | return -1; |
Jorge Lucangeli Obes | 1a122b8 | 2016-11-01 11:59:33 -0400 | [diff] [blame^] | 189 | } |
Jorge Lucangeli Obes | 66cfc14 | 2012-11-30 15:42:52 -0800 | [diff] [blame] | 190 | |
Jorge Lucangeli Obes | 1a122b8 | 2016-11-01 11:59:33 -0400 | [diff] [blame^] | 191 | /* Checks that there are no extra tokens. */ |
| 192 | const char *extra = strtok_r(NULL, " ", &atom_ptr); |
| 193 | if (extra != NULL) { |
| 194 | warn("extra token '%s'", extra); |
Jorge Lucangeli Obes | 66cfc14 | 2012-11-30 15:42:52 -0800 | [diff] [blame] | 195 | return -1; |
Jorge Lucangeli Obes | 1a122b8 | 2016-11-01 11:59:33 -0400 | [diff] [blame^] | 196 | } |
Jorge Lucangeli Obes | 66cfc14 | 2012-11-30 15:42:52 -0800 | [diff] [blame] | 197 | |
| 198 | if (strncmp(argidx_str, "arg", 3)) { |
Jorge Lucangeli Obes | 1a122b8 | 2016-11-01 11:59:33 -0400 | [diff] [blame^] | 199 | warn("invalid argument token '%s'", argidx_str); |
Jorge Lucangeli Obes | 66cfc14 | 2012-11-30 15:42:52 -0800 | [diff] [blame] | 200 | return -1; |
| 201 | } |
| 202 | |
| 203 | char *argidx_ptr; |
| 204 | long int argidx = strtol(argidx_str + 3, &argidx_ptr, 10); |
| 205 | /* |
Jorge Lucangeli Obes | 1a122b8 | 2016-11-01 11:59:33 -0400 | [diff] [blame^] | 206 | * Checks that an actual argument index was parsed, |
| 207 | * and that there was nothing left after the index. |
Jorge Lucangeli Obes | 66cfc14 | 2012-11-30 15:42:52 -0800 | [diff] [blame] | 208 | */ |
Jorge Lucangeli Obes | 1a122b8 | 2016-11-01 11:59:33 -0400 | [diff] [blame^] | 209 | if (argidx_ptr == argidx_str + 3 || *argidx_ptr != '\0') { |
| 210 | warn("invalid argument index '%s'", argidx_str + 3); |
| 211 | return -1; |
| 212 | } |
| 213 | |
| 214 | int op = str_to_op(operator_str); |
| 215 | if (op < MIN_OPERATOR) { |
| 216 | warn("invalid operator '%s'", operator_str); |
Jorge Lucangeli Obes | 66cfc14 | 2012-11-30 15:42:52 -0800 | [diff] [blame] | 217 | return -1; |
Jorge Lucangeli Obes | 5389540 | 2016-10-18 12:02:58 -0400 | [diff] [blame] | 218 | } |
Jorge Lucangeli Obes | 66cfc14 | 2012-11-30 15:42:52 -0800 | [diff] [blame] | 219 | |
Luis Hector Chavez | 40b2574 | 2013-09-22 19:44:06 -0700 | [diff] [blame] | 220 | char *constant_str_ptr; |
| 221 | long int c = parse_constant(constant_str, &constant_str_ptr); |
Jorge Lucangeli Obes | 5389540 | 2016-10-18 12:02:58 -0400 | [diff] [blame] | 222 | if (constant_str_ptr == constant_str) { |
| 223 | warn("invalid constant '%s'", constant_str); |
Luis Hector Chavez | 40b2574 | 2013-09-22 19:44:06 -0700 | [diff] [blame] | 224 | return -1; |
Jorge Lucangeli Obes | 5389540 | 2016-10-18 12:02:58 -0400 | [diff] [blame] | 225 | } |
Luis Hector Chavez | 40b2574 | 2013-09-22 19:44:06 -0700 | [diff] [blame] | 226 | |
Jorge Lucangeli Obes | 66cfc14 | 2012-11-30 15:42:52 -0800 | [diff] [blame] | 227 | /* |
| 228 | * Looks up the label for the end of the AND statement |
| 229 | * this atom belongs to. |
| 230 | */ |
Jorge Lucangeli Obes | 1a122b8 | 2016-11-01 11:59:33 -0400 | [diff] [blame^] | 231 | unsigned int id = group_end_lbl(labels, nr, grp_idx); |
Jorge Lucangeli Obes | 66cfc14 | 2012-11-30 15:42:52 -0800 | [diff] [blame] | 232 | |
| 233 | /* |
| 234 | * Builds a BPF comparison between a syscall argument |
| 235 | * and a constant. |
| 236 | * The comparison lives inside an AND statement. |
| 237 | * If the comparison succeeds, we continue |
| 238 | * to the next comparison. |
| 239 | * If this comparison fails, the whole AND statement |
| 240 | * will fail, so we jump to the end of this AND statement. |
| 241 | */ |
| 242 | struct sock_filter *comp_block; |
| 243 | size_t len = bpf_arg_comp(&comp_block, op, argidx, c, id); |
| 244 | if (len == 0) |
| 245 | return -1; |
| 246 | |
| 247 | append_filter_block(head, comp_block, len); |
| 248 | return 0; |
| 249 | } |
| 250 | |
Jorge Lucangeli Obes | 713f6fb | 2016-10-03 13:03:25 -0400 | [diff] [blame] | 251 | int compile_errno(struct filter_block *head, char *ret_errno, int use_ret_trap) |
Jorge Lucangeli Obes | c8b21e1 | 2014-06-13 14:26:16 -0700 | [diff] [blame] | 252 | { |
Jorge Lucangeli Obes | 66cfc14 | 2012-11-30 15:42:52 -0800 | [diff] [blame] | 253 | char *errno_ptr; |
| 254 | |
| 255 | /* Splits the 'return' keyword and the actual errno value. */ |
| 256 | char *ret_str = strtok_r(ret_errno, " ", &errno_ptr); |
| 257 | if (strncmp(ret_str, "return", strlen("return"))) |
| 258 | return -1; |
| 259 | |
| 260 | char *errno_val_str = strtok_r(NULL, " ", &errno_ptr); |
| 261 | |
| 262 | if (errno_val_str) { |
| 263 | char *errno_val_ptr; |
Luis Hector Chavez | 40b2574 | 2013-09-22 19:44:06 -0700 | [diff] [blame] | 264 | int errno_val = parse_constant(errno_val_str, &errno_val_ptr); |
Jorge Lucangeli Obes | 66cfc14 | 2012-11-30 15:42:52 -0800 | [diff] [blame] | 265 | /* Checks to see if we parsed an actual errno. */ |
Jorge Lucangeli Obes | 5389540 | 2016-10-18 12:02:58 -0400 | [diff] [blame] | 266 | if (errno_val_ptr == errno_val_str || errno_val == -1) { |
| 267 | warn("invalid errno value '%s'", errno_val_ptr); |
Jorge Lucangeli Obes | 66cfc14 | 2012-11-30 15:42:52 -0800 | [diff] [blame] | 268 | return -1; |
Jorge Lucangeli Obes | 5389540 | 2016-10-18 12:02:58 -0400 | [diff] [blame] | 269 | } |
Jorge Lucangeli Obes | 66cfc14 | 2012-11-30 15:42:52 -0800 | [diff] [blame] | 270 | |
| 271 | append_ret_errno(head, errno_val); |
| 272 | } else { |
Jorge Lucangeli Obes | 713f6fb | 2016-10-03 13:03:25 -0400 | [diff] [blame] | 273 | if (!use_ret_trap) |
Jennifer Pullman | c0bfae0 | 2016-05-26 17:00:36 -0700 | [diff] [blame] | 274 | append_ret_kill(head); |
| 275 | else |
| 276 | append_ret_trap(head); |
Jorge Lucangeli Obes | 66cfc14 | 2012-11-30 15:42:52 -0800 | [diff] [blame] | 277 | } |
| 278 | return 0; |
| 279 | } |
| 280 | |
Jorge Lucangeli Obes | d446726 | 2012-03-23 16:19:59 -0700 | [diff] [blame] | 281 | struct filter_block *compile_section(int nr, const char *policy_line, |
Jorge Lucangeli Obes | 565e978 | 2016-08-05 11:03:19 -0400 | [diff] [blame] | 282 | unsigned int entry_lbl_id, |
Jennifer Pullman | c0bfae0 | 2016-05-26 17:00:36 -0700 | [diff] [blame] | 283 | struct bpf_labels *labels, |
Jorge Lucangeli Obes | 713f6fb | 2016-10-03 13:03:25 -0400 | [diff] [blame] | 284 | int use_ret_trap) |
Jorge Lucangeli Obes | fc8ab53 | 2012-03-20 10:14:31 -0700 | [diff] [blame] | 285 | { |
| 286 | /* |
| 287 | * |policy_line| should be an expression of the form: |
| 288 | * "arg0 == 3 && arg1 == 5 || arg0 == 0x8" |
| 289 | * |
| 290 | * This is, an expression in DNF (disjunctive normal form); |
| 291 | * a disjunction ('||') of one or more conjunctions ('&&') |
| 292 | * of one or more atoms. |
| 293 | * |
Jorge Lucangeli Obes | d96baf4 | 2013-03-26 15:11:30 -0700 | [diff] [blame] | 294 | * Atoms are of the form "arg{DNUM} {OP} {NUM}" |
Jorge Lucangeli Obes | fc8ab53 | 2012-03-20 10:14:31 -0700 | [diff] [blame] | 295 | * where: |
| 296 | * - DNUM is a decimal number. |
Jorge Lucangeli Obes | 21c3ab1 | 2016-10-12 18:37:37 -0400 | [diff] [blame] | 297 | * - OP is an operator: ==, !=, & (flags set), or 'in' (inclusion). |
Jorge Lucangeli Obes | 66cfc14 | 2012-11-30 15:42:52 -0800 | [diff] [blame] | 298 | * - NUM is an octal, decimal, or hexadecimal number. |
Jorge Lucangeli Obes | fc8ab53 | 2012-03-20 10:14:31 -0700 | [diff] [blame] | 299 | * |
| 300 | * When the syscall arguments make the expression true, |
| 301 | * the syscall is allowed. If not, the process is killed. |
| 302 | * |
Jorge Lucangeli Obes | d96baf4 | 2013-03-26 15:11:30 -0700 | [diff] [blame] | 303 | * To block a syscall without killing the process, |
| 304 | * |policy_line| can be of the form: |
| 305 | * "return <errno>" |
Jorge Lucangeli Obes | fc8ab53 | 2012-03-20 10:14:31 -0700 | [diff] [blame] | 306 | * |
Jorge Lucangeli Obes | d96baf4 | 2013-03-26 15:11:30 -0700 | [diff] [blame] | 307 | * This "return {NUM}" policy line will block the syscall, |
| 308 | * make it return -1 and set |errno| to NUM. |
| 309 | * |
| 310 | * A regular policy line can also include a "return <errno>" clause, |
| 311 | * separated by a semicolon (';'): |
Jorge Lucangeli Obes | fc8ab53 | 2012-03-20 10:14:31 -0700 | [diff] [blame] | 312 | * "arg0 == 3 && arg1 == 5 || arg0 == 0x8; return {NUM}" |
| 313 | * |
Jorge Lucangeli Obes | d96baf4 | 2013-03-26 15:11:30 -0700 | [diff] [blame] | 314 | * If the syscall arguments don't make the expression true, |
| 315 | * the syscall will be blocked as above instead of killing the process. |
Jorge Lucangeli Obes | fc8ab53 | 2012-03-20 10:14:31 -0700 | [diff] [blame] | 316 | */ |
| 317 | |
| 318 | size_t len = 0; |
Jorge Lucangeli Obes | 1a122b8 | 2016-11-01 11:59:33 -0400 | [diff] [blame^] | 319 | int grp_idx = 0; |
| 320 | |
| 321 | /* Checks for empty policy lines. */ |
| 322 | if (strlen(policy_line) == 0) { |
| 323 | warn("empty policy line"); |
| 324 | return NULL; |
| 325 | } |
Jorge Lucangeli Obes | fc8ab53 | 2012-03-20 10:14:31 -0700 | [diff] [blame] | 326 | |
| 327 | /* Checks for overly long policy lines. */ |
Jorge Lucangeli Obes | bda833c | 2012-07-31 16:25:56 -0700 | [diff] [blame] | 328 | if (strlen(policy_line) >= MAX_POLICY_LINE_LENGTH) |
Jorge Lucangeli Obes | fc8ab53 | 2012-03-20 10:14:31 -0700 | [diff] [blame] | 329 | return NULL; |
| 330 | |
Jorge Lucangeli Obes | d96baf4 | 2013-03-26 15:11:30 -0700 | [diff] [blame] | 331 | /* We will modify |policy_line|, so let's make a copy. */ |
Jorge Lucangeli Obes | bda833c | 2012-07-31 16:25:56 -0700 | [diff] [blame] | 332 | char *line = strndup(policy_line, MAX_POLICY_LINE_LENGTH); |
Jorge Lucangeli Obes | fc8ab53 | 2012-03-20 10:14:31 -0700 | [diff] [blame] | 333 | if (!line) |
| 334 | return NULL; |
| 335 | |
Jorge Lucangeli Obes | fc8ab53 | 2012-03-20 10:14:31 -0700 | [diff] [blame] | 336 | /* |
Jorge Lucangeli Obes | d96baf4 | 2013-03-26 15:11:30 -0700 | [diff] [blame] | 337 | * We build the filter section as a collection of smaller |
Jorge Lucangeli Obes | fc8ab53 | 2012-03-20 10:14:31 -0700 | [diff] [blame] | 338 | * "filter blocks" linked together in a singly-linked list. |
| 339 | */ |
Jorge Lucangeli Obes | d96baf4 | 2013-03-26 15:11:30 -0700 | [diff] [blame] | 340 | struct filter_block *head = new_filter_block(); |
Jorge Lucangeli Obes | fc8ab53 | 2012-03-20 10:14:31 -0700 | [diff] [blame] | 341 | |
| 342 | /* |
Jorge Lucangeli Obes | d96baf4 | 2013-03-26 15:11:30 -0700 | [diff] [blame] | 343 | * Filter sections begin with a label where the main filter |
Jorge Lucangeli Obes | fc8ab53 | 2012-03-20 10:14:31 -0700 | [diff] [blame] | 344 | * will jump after checking the syscall number. |
| 345 | */ |
| 346 | struct sock_filter *entry_label = new_instr_buf(ONE_INSTR); |
| 347 | set_bpf_lbl(entry_label, entry_lbl_id); |
| 348 | append_filter_block(head, entry_label, ONE_INSTR); |
| 349 | |
Jorge Lucangeli Obes | d96baf4 | 2013-03-26 15:11:30 -0700 | [diff] [blame] | 350 | /* Checks whether we're unconditionally blocking this syscall. */ |
| 351 | if (strncmp(line, "return", strlen("return")) == 0) { |
Jorge Lucangeli Obes | 1a122b8 | 2016-11-01 11:59:33 -0400 | [diff] [blame^] | 352 | if (compile_errno(head, line, use_ret_trap) < 0) { |
| 353 | free_block_list(head); |
| 354 | free(line); |
Jorge Lucangeli Obes | d96baf4 | 2013-03-26 15:11:30 -0700 | [diff] [blame] | 355 | return NULL; |
Jorge Lucangeli Obes | 1a122b8 | 2016-11-01 11:59:33 -0400 | [diff] [blame^] | 356 | } |
Jorge Lucangeli Obes | d96baf4 | 2013-03-26 15:11:30 -0700 | [diff] [blame] | 357 | free(line); |
| 358 | return head; |
| 359 | } |
| 360 | |
| 361 | /* Splits the optional "return <errno>" part. */ |
| 362 | char *line_ptr; |
| 363 | char *arg_filter = strtok_r(line, ";", &line_ptr); |
| 364 | char *ret_errno = strtok_r(NULL, ";", &line_ptr); |
| 365 | |
Jorge Lucangeli Obes | fc8ab53 | 2012-03-20 10:14:31 -0700 | [diff] [blame] | 366 | /* |
| 367 | * Splits the policy line by '||' into conjunctions and each conjunction |
| 368 | * by '&&' into atoms. |
| 369 | */ |
Jorge Lucangeli Obes | 66cfc14 | 2012-11-30 15:42:52 -0800 | [diff] [blame] | 370 | char *arg_filter_str = arg_filter; |
| 371 | char *group; |
| 372 | while ((group = tokenize(&arg_filter_str, "||")) != NULL) { |
| 373 | char *group_str = group; |
| 374 | char *comp; |
| 375 | while ((comp = tokenize(&group_str, "&&")) != NULL) { |
| 376 | /* Compiles each atom into a BPF block. */ |
Jorge Lucangeli Obes | 1a122b8 | 2016-11-01 11:59:33 -0400 | [diff] [blame^] | 377 | if (compile_atom(head, comp, labels, nr, grp_idx) < 0) { |
| 378 | free_block_list(head); |
| 379 | free(line); |
Jorge Lucangeli Obes | fc8ab53 | 2012-03-20 10:14:31 -0700 | [diff] [blame] | 380 | return NULL; |
Jorge Lucangeli Obes | 1a122b8 | 2016-11-01 11:59:33 -0400 | [diff] [blame^] | 381 | } |
Jorge Lucangeli Obes | fc8ab53 | 2012-03-20 10:14:31 -0700 | [diff] [blame] | 382 | } |
| 383 | /* |
| 384 | * If the AND statement succeeds, we're done, |
| 385 | * so jump to SUCCESS line. |
| 386 | */ |
Jorge Lucangeli Obes | d446726 | 2012-03-23 16:19:59 -0700 | [diff] [blame] | 387 | unsigned int id = success_lbl(labels, nr); |
Jorge Lucangeli Obes | fc8ab53 | 2012-03-20 10:14:31 -0700 | [diff] [blame] | 388 | struct sock_filter *group_end_block = new_instr_buf(TWO_INSTRS); |
| 389 | len = set_bpf_jump_lbl(group_end_block, id); |
| 390 | /* |
| 391 | * The end of each AND statement falls after the |
| 392 | * jump to SUCCESS. |
| 393 | */ |
Jorge Lucangeli Obes | 1a122b8 | 2016-11-01 11:59:33 -0400 | [diff] [blame^] | 394 | id = group_end_lbl(labels, nr, grp_idx++); |
Jorge Lucangeli Obes | fc8ab53 | 2012-03-20 10:14:31 -0700 | [diff] [blame] | 395 | len += set_bpf_lbl(group_end_block + len, id); |
| 396 | append_filter_block(head, group_end_block, len); |
| 397 | } |
| 398 | |
| 399 | /* |
| 400 | * If no AND statements succeed, we end up here, |
| 401 | * because we never jumped to SUCCESS. |
| 402 | * If we have to return an errno, do it, |
| 403 | * otherwise just kill the task. |
| 404 | */ |
| 405 | if (ret_errno) { |
Jorge Lucangeli Obes | 1a122b8 | 2016-11-01 11:59:33 -0400 | [diff] [blame^] | 406 | if (compile_errno(head, ret_errno, use_ret_trap) < 0) { |
| 407 | free_block_list(head); |
| 408 | free(line); |
Jorge Lucangeli Obes | fc8ab53 | 2012-03-20 10:14:31 -0700 | [diff] [blame] | 409 | return NULL; |
Jorge Lucangeli Obes | 1a122b8 | 2016-11-01 11:59:33 -0400 | [diff] [blame^] | 410 | } |
Jorge Lucangeli Obes | fc8ab53 | 2012-03-20 10:14:31 -0700 | [diff] [blame] | 411 | } else { |
Jorge Lucangeli Obes | 713f6fb | 2016-10-03 13:03:25 -0400 | [diff] [blame] | 412 | if (!use_ret_trap) |
Jennifer Pullman | c0bfae0 | 2016-05-26 17:00:36 -0700 | [diff] [blame] | 413 | append_ret_kill(head); |
| 414 | else |
| 415 | append_ret_trap(head); |
Jorge Lucangeli Obes | fc8ab53 | 2012-03-20 10:14:31 -0700 | [diff] [blame] | 416 | } |
| 417 | |
| 418 | /* |
| 419 | * Every time the filter succeeds we jump to a predefined SUCCESS |
| 420 | * label. Add that label and BPF RET_ALLOW code now. |
| 421 | */ |
Jorge Lucangeli Obes | d446726 | 2012-03-23 16:19:59 -0700 | [diff] [blame] | 422 | unsigned int id = success_lbl(labels, nr); |
Jorge Lucangeli Obes | fc8ab53 | 2012-03-20 10:14:31 -0700 | [diff] [blame] | 423 | struct sock_filter *success_block = new_instr_buf(TWO_INSTRS); |
| 424 | len = set_bpf_lbl(success_block, id); |
| 425 | len += set_bpf_ret_allow(success_block + len); |
| 426 | append_filter_block(head, success_block, len); |
| 427 | |
| 428 | free(line); |
| 429 | return head; |
| 430 | } |
| 431 | |
Jorge Lucangeli Obes | 713f6fb | 2016-10-03 13:03:25 -0400 | [diff] [blame] | 432 | int compile_filter(FILE *policy_file, struct sock_fprog *prog, int use_ret_trap, |
| 433 | int allow_logging) |
Jorge Lucangeli Obes | d446726 | 2012-03-23 16:19:59 -0700 | [diff] [blame] | 434 | { |
| 435 | char line[MAX_LINE_LENGTH]; |
| 436 | int line_count = 0; |
| 437 | |
| 438 | struct bpf_labels labels; |
| 439 | labels.count = 0; |
| 440 | |
Jorge Lucangeli Obes | b0cea43 | 2013-02-04 11:55:30 -0800 | [diff] [blame] | 441 | if (!policy_file) |
Jorge Lucangeli Obes | 6135db9 | 2012-07-27 13:37:30 -0700 | [diff] [blame] | 442 | return -1; |
| 443 | |
Jorge Lucangeli Obes | d96baf4 | 2013-03-26 15:11:30 -0700 | [diff] [blame] | 444 | struct filter_block *head = new_filter_block(); |
Jorge Lucangeli Obes | d446726 | 2012-03-23 16:19:59 -0700 | [diff] [blame] | 445 | struct filter_block *arg_blocks = NULL; |
| 446 | |
| 447 | /* Start filter by validating arch. */ |
| 448 | struct sock_filter *valid_arch = new_instr_buf(ARCH_VALIDATION_LEN); |
| 449 | size_t len = bpf_validate_arch(valid_arch); |
| 450 | append_filter_block(head, valid_arch, len); |
| 451 | |
Jorge Lucangeli Obes | bda833c | 2012-07-31 16:25:56 -0700 | [diff] [blame] | 452 | /* Load syscall number. */ |
Jorge Lucangeli Obes | d446726 | 2012-03-23 16:19:59 -0700 | [diff] [blame] | 453 | struct sock_filter *load_nr = new_instr_buf(ONE_INSTR); |
| 454 | len = bpf_load_syscall_nr(load_nr); |
| 455 | append_filter_block(head, load_nr, len); |
| 456 | |
Jorge Lucangeli Obes | 713f6fb | 2016-10-03 13:03:25 -0400 | [diff] [blame] | 457 | /* If logging failures, allow the necessary syscalls first. */ |
| 458 | if (allow_logging) |
| 459 | allow_logging_syscalls(head); |
Jorge Lucangeli Obes | bda833c | 2012-07-31 16:25:56 -0700 | [diff] [blame] | 460 | |
Jorge Lucangeli Obes | d446726 | 2012-03-23 16:19:59 -0700 | [diff] [blame] | 461 | /* |
| 462 | * Loop through all the lines in the policy file. |
| 463 | * Build a jump table for the syscall number. |
| 464 | * If the policy line has an arg filter, build the arg filter |
| 465 | * as well. |
| 466 | * Chain the filter sections together and dump them into |
| 467 | * the final buffer at the end. |
| 468 | */ |
Jorge Lucangeli Obes | b0cea43 | 2013-02-04 11:55:30 -0800 | [diff] [blame] | 469 | while (fgets(line, sizeof(line), policy_file)) { |
Jorge Lucangeli Obes | d446726 | 2012-03-23 16:19:59 -0700 | [diff] [blame] | 470 | ++line_count; |
Jorge Lucangeli Obes | b0cea43 | 2013-02-04 11:55:30 -0800 | [diff] [blame] | 471 | char *policy_line = line; |
| 472 | char *syscall_name = strsep(&policy_line, ":"); |
Jorge Lucangeli Obes | d446726 | 2012-03-23 16:19:59 -0700 | [diff] [blame] | 473 | int nr = -1; |
| 474 | |
| 475 | syscall_name = strip(syscall_name); |
| 476 | |
| 477 | /* Allow comments and empty lines. */ |
| 478 | if (*syscall_name == '#' || *syscall_name == '\0') |
| 479 | continue; |
| 480 | |
Jorge Lucangeli Obes | 1a122b8 | 2016-11-01 11:59:33 -0400 | [diff] [blame^] | 481 | if (strlen(policy_line) == 0) { |
| 482 | warn("compile_filter: empty policy line"); |
| 483 | free_block_list(head); |
Jorge Lucangeli Obes | d446726 | 2012-03-23 16:19:59 -0700 | [diff] [blame] | 484 | return -1; |
Jorge Lucangeli Obes | 1a122b8 | 2016-11-01 11:59:33 -0400 | [diff] [blame^] | 485 | } |
Jorge Lucangeli Obes | d446726 | 2012-03-23 16:19:59 -0700 | [diff] [blame] | 486 | |
| 487 | nr = lookup_syscall(syscall_name); |
Jorge Lucangeli Obes | 275b07f | 2012-08-28 11:50:29 -0700 | [diff] [blame] | 488 | if (nr < 0) { |
| 489 | warn("compile_filter: nonexistent syscall '%s'", |
| 490 | syscall_name); |
Jorge Lucangeli Obes | 713f6fb | 2016-10-03 13:03:25 -0400 | [diff] [blame] | 491 | if (allow_logging) { |
Jorge Lucangeli Obes | be351a2 | 2016-01-22 17:18:51 -0800 | [diff] [blame] | 492 | /* |
| 493 | * If we're logging failures, assume we're in a |
| 494 | * debugging case and continue. |
| 495 | * This is not super risky because an invalid |
| 496 | * syscall name is likely caused by a typo or by |
| 497 | * leftover lines from a different architecture. |
| 498 | * In either case, not including a policy line |
| 499 | * is equivalent to killing the process if the |
| 500 | * syscall is made, so there's no added attack |
| 501 | * surface. |
| 502 | */ |
| 503 | continue; |
| 504 | } |
Jorge Lucangeli Obes | 1a122b8 | 2016-11-01 11:59:33 -0400 | [diff] [blame^] | 505 | free_block_list(head); |
Jorge Lucangeli Obes | d446726 | 2012-03-23 16:19:59 -0700 | [diff] [blame] | 506 | return -1; |
Jorge Lucangeli Obes | 275b07f | 2012-08-28 11:50:29 -0700 | [diff] [blame] | 507 | } |
Jorge Lucangeli Obes | d446726 | 2012-03-23 16:19:59 -0700 | [diff] [blame] | 508 | |
Jorge Lucangeli Obes | b0cea43 | 2013-02-04 11:55:30 -0800 | [diff] [blame] | 509 | policy_line = strip(policy_line); |
Jorge Lucangeli Obes | d446726 | 2012-03-23 16:19:59 -0700 | [diff] [blame] | 510 | |
| 511 | /* |
| 512 | * For each syscall, add either a simple ALLOW, |
| 513 | * or an arg filter block. |
| 514 | */ |
Jorge Lucangeli Obes | b0cea43 | 2013-02-04 11:55:30 -0800 | [diff] [blame] | 515 | if (strcmp(policy_line, "1") == 0) { |
Jorge Lucangeli Obes | d446726 | 2012-03-23 16:19:59 -0700 | [diff] [blame] | 516 | /* Add simple ALLOW. */ |
Jorge Lucangeli Obes | bda833c | 2012-07-31 16:25:56 -0700 | [diff] [blame] | 517 | append_allow_syscall(head, nr); |
Jorge Lucangeli Obes | d446726 | 2012-03-23 16:19:59 -0700 | [diff] [blame] | 518 | } else { |
| 519 | /* |
| 520 | * Create and jump to the label that will hold |
| 521 | * the arg filter block. |
| 522 | */ |
| 523 | unsigned int id = bpf_label_id(&labels, syscall_name); |
| 524 | struct sock_filter *nr_comp = |
Jorge Lucangeli Obes | 565e978 | 2016-08-05 11:03:19 -0400 | [diff] [blame] | 525 | new_instr_buf(ALLOW_SYSCALL_LEN); |
Jorge Lucangeli Obes | d446726 | 2012-03-23 16:19:59 -0700 | [diff] [blame] | 526 | bpf_allow_syscall_args(nr_comp, nr, id); |
| 527 | append_filter_block(head, nr_comp, ALLOW_SYSCALL_LEN); |
| 528 | |
| 529 | /* Build the arg filter block. */ |
Jorge Lucangeli Obes | 3dc257c | 2016-11-01 12:25:04 -0400 | [diff] [blame] | 530 | struct filter_block *block = compile_section( |
| 531 | nr, policy_line, id, &labels, use_ret_trap); |
Jorge Lucangeli Obes | d446726 | 2012-03-23 16:19:59 -0700 | [diff] [blame] | 532 | |
Jorge Lucangeli Obes | 1a122b8 | 2016-11-01 11:59:33 -0400 | [diff] [blame^] | 533 | if (!block) { |
| 534 | if (arg_blocks) { |
| 535 | free_block_list(arg_blocks); |
| 536 | } |
| 537 | free_label_strings(&labels); |
| 538 | free_block_list(head); |
Jorge Lucangeli Obes | d446726 | 2012-03-23 16:19:59 -0700 | [diff] [blame] | 539 | return -1; |
Jorge Lucangeli Obes | 1a122b8 | 2016-11-01 11:59:33 -0400 | [diff] [blame^] | 540 | } |
Jorge Lucangeli Obes | d446726 | 2012-03-23 16:19:59 -0700 | [diff] [blame] | 541 | |
| 542 | if (arg_blocks) { |
| 543 | extend_filter_block_list(arg_blocks, block); |
| 544 | } else { |
| 545 | arg_blocks = block; |
| 546 | } |
| 547 | } |
| 548 | } |
| 549 | |
Jorge Lucangeli Obes | bda833c | 2012-07-31 16:25:56 -0700 | [diff] [blame] | 550 | /* |
Jorge Lucangeli Obes | 713f6fb | 2016-10-03 13:03:25 -0400 | [diff] [blame] | 551 | * If none of the syscalls match, either fall through to KILL, |
Jorge Lucangeli Obes | bda833c | 2012-07-31 16:25:56 -0700 | [diff] [blame] | 552 | * or return TRAP. |
| 553 | */ |
Jorge Lucangeli Obes | 713f6fb | 2016-10-03 13:03:25 -0400 | [diff] [blame] | 554 | if (!use_ret_trap) |
Jorge Lucangeli Obes | bda833c | 2012-07-31 16:25:56 -0700 | [diff] [blame] | 555 | append_ret_kill(head); |
| 556 | else |
| 557 | append_ret_trap(head); |
Jorge Lucangeli Obes | d446726 | 2012-03-23 16:19:59 -0700 | [diff] [blame] | 558 | |
| 559 | /* Allocate the final buffer, now that we know its size. */ |
Jorge Lucangeli Obes | 565e978 | 2016-08-05 11:03:19 -0400 | [diff] [blame] | 560 | size_t final_filter_len = |
| 561 | head->total_len + (arg_blocks ? arg_blocks->total_len : 0); |
Jorge Lucangeli Obes | d446726 | 2012-03-23 16:19:59 -0700 | [diff] [blame] | 562 | if (final_filter_len > BPF_MAXINSNS) |
| 563 | return -1; |
| 564 | |
| 565 | struct sock_filter *final_filter = |
Jorge Lucangeli Obes | 565e978 | 2016-08-05 11:03:19 -0400 | [diff] [blame] | 566 | calloc(final_filter_len, sizeof(struct sock_filter)); |
Jorge Lucangeli Obes | d446726 | 2012-03-23 16:19:59 -0700 | [diff] [blame] | 567 | |
| 568 | if (flatten_block_list(head, final_filter, 0, final_filter_len) < 0) |
| 569 | return -1; |
| 570 | |
Jorge Lucangeli Obes | 565e978 | 2016-08-05 11:03:19 -0400 | [diff] [blame] | 571 | if (flatten_block_list(arg_blocks, final_filter, head->total_len, |
| 572 | final_filter_len) < 0) |
Jorge Lucangeli Obes | d446726 | 2012-03-23 16:19:59 -0700 | [diff] [blame] | 573 | return -1; |
| 574 | |
| 575 | free_block_list(head); |
| 576 | free_block_list(arg_blocks); |
| 577 | |
Jorge Lucangeli Obes | 8cc9d4a | 2016-10-03 10:00:57 -0400 | [diff] [blame] | 578 | if (bpf_resolve_jumps(&labels, final_filter, final_filter_len) < 0) |
| 579 | return -1; |
Jorge Lucangeli Obes | d446726 | 2012-03-23 16:19:59 -0700 | [diff] [blame] | 580 | |
| 581 | free_label_strings(&labels); |
| 582 | |
| 583 | prog->filter = final_filter; |
| 584 | prog->len = final_filter_len; |
| 585 | return 0; |
| 586 | } |
| 587 | |
| 588 | int flatten_block_list(struct filter_block *head, struct sock_filter *filter, |
Jorge Lucangeli Obes | 565e978 | 2016-08-05 11:03:19 -0400 | [diff] [blame] | 589 | size_t index, size_t cap) |
Jorge Lucangeli Obes | d446726 | 2012-03-23 16:19:59 -0700 | [diff] [blame] | 590 | { |
| 591 | size_t _index = index; |
| 592 | |
| 593 | struct filter_block *curr; |
| 594 | size_t i; |
| 595 | |
| 596 | for (curr = head; curr; curr = curr->next) { |
| 597 | for (i = 0; i < curr->len; i++) { |
| 598 | if (_index >= cap) |
| 599 | return -1; |
| 600 | filter[_index++] = curr->instrs[i]; |
| 601 | } |
| 602 | } |
| 603 | return 0; |
| 604 | } |
| 605 | |
Jorge Lucangeli Obes | fc8ab53 | 2012-03-20 10:14:31 -0700 | [diff] [blame] | 606 | void free_block_list(struct filter_block *head) |
| 607 | { |
| 608 | struct filter_block *current, *prev; |
| 609 | |
| 610 | current = head; |
| 611 | while (current) { |
| 612 | free(current->instrs); |
| 613 | prev = current; |
| 614 | current = current->next; |
| 615 | free(prev); |
| 616 | } |
| 617 | } |