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 | bda833c | 2012-07-31 16:25:56 -0700 | [diff] [blame] | 15 | #define MAX_POLICY_LINE_LENGTH 1024 |
| 16 | |
Jorge Lucangeli Obes | a6b034d | 2012-08-07 15:29:20 -0700 | [diff] [blame] | 17 | #define ONE_INSTR 1 |
| 18 | #define TWO_INSTRS 2 |
Jorge Lucangeli Obes | 3dc257c | 2016-11-01 12:25:04 -0400 | [diff] [blame] | 19 | /* clang-format on */ |
Jorge Lucangeli Obes | d446726 | 2012-03-23 16:19:59 -0700 | [diff] [blame] | 20 | |
Jorge Lucangeli Obes | 45932a5 | 2017-03-15 17:02:58 -0400 | [diff] [blame] | 21 | int seccomp_can_softfail(void) |
Jorge Lucangeli Obes | 7b2e29c | 2016-08-04 12:21:03 -0400 | [diff] [blame] | 22 | { |
Jorge Lucangeli Obes | 565e978 | 2016-08-05 11:03:19 -0400 | [diff] [blame] | 23 | #if defined(USE_SECCOMP_SOFTFAIL) |
Jeff Vander Stoep | 1022fc3 | 2016-08-28 12:24:55 -0700 | [diff] [blame] | 24 | return 1; |
Jorge Lucangeli Obes | 7b2e29c | 2016-08-04 12:21:03 -0400 | [diff] [blame] | 25 | #endif |
| 26 | return 0; |
| 27 | } |
| 28 | |
Jorge Lucangeli Obes | fc8ab53 | 2012-03-20 10:14:31 -0700 | [diff] [blame] | 29 | int str_to_op(const char *op_str) |
| 30 | { |
| 31 | if (!strcmp(op_str, "==")) { |
| 32 | return EQ; |
| 33 | } else if (!strcmp(op_str, "!=")) { |
| 34 | return NE; |
Jorge Lucangeli Obes | 66cfc14 | 2012-11-30 15:42:52 -0800 | [diff] [blame] | 35 | } else if (!strcmp(op_str, "&")) { |
| 36 | return SET; |
Jorge Lucangeli Obes | fd6f8e3 | 2016-10-12 11:19:28 -0400 | [diff] [blame] | 37 | } else if (!strcmp(op_str, "in")) { |
| 38 | return IN; |
Jorge Lucangeli Obes | fc8ab53 | 2012-03-20 10:14:31 -0700 | [diff] [blame] | 39 | } else { |
| 40 | return 0; |
| 41 | } |
| 42 | } |
| 43 | |
Jorge Lucangeli Obes | fc8ab53 | 2012-03-20 10:14:31 -0700 | [diff] [blame] | 44 | struct sock_filter *new_instr_buf(size_t count) |
| 45 | { |
| 46 | struct sock_filter *buf = calloc(count, sizeof(struct sock_filter)); |
| 47 | if (!buf) |
Jorge Lucangeli Obes | 224e427 | 2012-08-02 14:31:39 -0700 | [diff] [blame] | 48 | die("could not allocate BPF instruction buffer"); |
Jorge Lucangeli Obes | fc8ab53 | 2012-03-20 10:14:31 -0700 | [diff] [blame] | 49 | |
| 50 | return buf; |
| 51 | } |
| 52 | |
Jorge Lucangeli Obes | 45932a5 | 2017-03-15 17:02:58 -0400 | [diff] [blame] | 53 | struct filter_block *new_filter_block(void) |
Jorge Lucangeli Obes | d96baf4 | 2013-03-26 15:11:30 -0700 | [diff] [blame] | 54 | { |
| 55 | struct filter_block *block = calloc(1, sizeof(struct filter_block)); |
| 56 | if (!block) |
| 57 | die("could not allocate BPF filter block"); |
| 58 | |
| 59 | block->instrs = NULL; |
| 60 | block->last = block->next = NULL; |
| 61 | |
| 62 | return block; |
| 63 | } |
| 64 | |
Jorge Lucangeli Obes | 565e978 | 2016-08-05 11:03:19 -0400 | [diff] [blame] | 65 | void append_filter_block(struct filter_block *head, struct sock_filter *instrs, |
| 66 | size_t len) |
Jorge Lucangeli Obes | fc8ab53 | 2012-03-20 10:14:31 -0700 | [diff] [blame] | 67 | { |
| 68 | struct filter_block *new_last; |
| 69 | |
| 70 | /* |
| 71 | * If |head| has no filter assigned yet, |
| 72 | * we don't create a new node. |
| 73 | */ |
| 74 | if (head->instrs == NULL) { |
| 75 | new_last = head; |
| 76 | } else { |
Jorge Lucangeli Obes | d96baf4 | 2013-03-26 15:11:30 -0700 | [diff] [blame] | 77 | new_last = new_filter_block(); |
Jorge Lucangeli Obes | fc8ab53 | 2012-03-20 10:14:31 -0700 | [diff] [blame] | 78 | if (head->next != NULL) { |
| 79 | head->last->next = new_last; |
| 80 | head->last = new_last; |
| 81 | } else { |
| 82 | head->last = head->next = new_last; |
| 83 | } |
| 84 | head->total_len += len; |
| 85 | } |
| 86 | |
| 87 | new_last->instrs = instrs; |
| 88 | new_last->total_len = new_last->len = len; |
| 89 | new_last->last = new_last->next = NULL; |
| 90 | } |
| 91 | |
Jorge Lucangeli Obes | d446726 | 2012-03-23 16:19:59 -0700 | [diff] [blame] | 92 | void extend_filter_block_list(struct filter_block *list, |
Jorge Lucangeli Obes | 565e978 | 2016-08-05 11:03:19 -0400 | [diff] [blame] | 93 | struct filter_block *another) |
Jorge Lucangeli Obes | d446726 | 2012-03-23 16:19:59 -0700 | [diff] [blame] | 94 | { |
| 95 | if (list->last != NULL) { |
| 96 | list->last->next = another; |
| 97 | list->last = another->last; |
| 98 | } else { |
| 99 | list->next = another; |
| 100 | list->last = another->last; |
| 101 | } |
| 102 | list->total_len += another->total_len; |
| 103 | } |
| 104 | |
Jorge Lucangeli Obes | fc8ab53 | 2012-03-20 10:14:31 -0700 | [diff] [blame] | 105 | void append_ret_kill(struct filter_block *head) |
| 106 | { |
| 107 | struct sock_filter *filter = new_instr_buf(ONE_INSTR); |
| 108 | set_bpf_ret_kill(filter); |
| 109 | append_filter_block(head, filter, ONE_INSTR); |
| 110 | } |
| 111 | |
Jorge Lucangeli Obes | bda833c | 2012-07-31 16:25:56 -0700 | [diff] [blame] | 112 | void append_ret_trap(struct filter_block *head) |
| 113 | { |
| 114 | struct sock_filter *filter = new_instr_buf(ONE_INSTR); |
| 115 | set_bpf_ret_trap(filter); |
| 116 | append_filter_block(head, filter, ONE_INSTR); |
| 117 | } |
| 118 | |
Jorge Lucangeli Obes | fc8ab53 | 2012-03-20 10:14:31 -0700 | [diff] [blame] | 119 | void append_ret_errno(struct filter_block *head, int errno_val) |
| 120 | { |
| 121 | struct sock_filter *filter = new_instr_buf(ONE_INSTR); |
| 122 | set_bpf_ret_errno(filter, errno_val); |
| 123 | append_filter_block(head, filter, ONE_INSTR); |
| 124 | } |
| 125 | |
Jorge Lucangeli Obes | c8b21e1 | 2014-06-13 14:26:16 -0700 | [diff] [blame] | 126 | void append_allow_syscall(struct filter_block *head, int nr) |
| 127 | { |
Jorge Lucangeli Obes | bda833c | 2012-07-31 16:25:56 -0700 | [diff] [blame] | 128 | struct sock_filter *filter = new_instr_buf(ALLOW_SYSCALL_LEN); |
| 129 | size_t len = bpf_allow_syscall(filter, nr); |
| 130 | if (len != ALLOW_SYSCALL_LEN) |
| 131 | die("error building syscall number comparison"); |
| 132 | |
| 133 | append_filter_block(head, filter, len); |
| 134 | } |
| 135 | |
Jorge Lucangeli Obes | 713f6fb | 2016-10-03 13:03:25 -0400 | [diff] [blame] | 136 | void allow_logging_syscalls(struct filter_block *head) |
Jorge Lucangeli Obes | bda833c | 2012-07-31 16:25:56 -0700 | [diff] [blame] | 137 | { |
| 138 | unsigned int i; |
Kees Cook | 03b2af2 | 2014-12-18 17:11:13 -0800 | [diff] [blame] | 139 | for (i = 0; i < log_syscalls_len; i++) { |
| 140 | warn("allowing syscall: %s", log_syscalls[i]); |
Jorge Lucangeli Obes | bda833c | 2012-07-31 16:25:56 -0700 | [diff] [blame] | 141 | append_allow_syscall(head, lookup_syscall(log_syscalls[i])); |
Kees Cook | 03b2af2 | 2014-12-18 17:11:13 -0800 | [diff] [blame] | 142 | } |
Jorge Lucangeli Obes | bda833c | 2012-07-31 16:25:56 -0700 | [diff] [blame] | 143 | } |
| 144 | |
Jorge Lucangeli Obes | fc8ab53 | 2012-03-20 10:14:31 -0700 | [diff] [blame] | 145 | unsigned int get_label_id(struct bpf_labels *labels, const char *label_str) |
| 146 | { |
| 147 | int label_id = bpf_label_id(labels, label_str); |
| 148 | if (label_id < 0) |
Jorge Lucangeli Obes | 224e427 | 2012-08-02 14:31:39 -0700 | [diff] [blame] | 149 | die("could not allocate BPF label string"); |
Jorge Lucangeli Obes | fc8ab53 | 2012-03-20 10:14:31 -0700 | [diff] [blame] | 150 | return label_id; |
| 151 | } |
| 152 | |
| 153 | unsigned int group_end_lbl(struct bpf_labels *labels, int nr, int idx) |
| 154 | { |
| 155 | char lbl_str[MAX_BPF_LABEL_LEN]; |
| 156 | snprintf(lbl_str, MAX_BPF_LABEL_LEN, "%d_%d_end", nr, idx); |
| 157 | return get_label_id(labels, lbl_str); |
| 158 | } |
| 159 | |
| 160 | unsigned int success_lbl(struct bpf_labels *labels, int nr) |
| 161 | { |
| 162 | char lbl_str[MAX_BPF_LABEL_LEN]; |
| 163 | snprintf(lbl_str, MAX_BPF_LABEL_LEN, "%d_success", nr); |
| 164 | return get_label_id(labels, lbl_str); |
| 165 | } |
| 166 | |
Jorge Lucangeli Obes | 66cfc14 | 2012-11-30 15:42:52 -0800 | [diff] [blame] | 167 | int compile_atom(struct filter_block *head, char *atom, |
Jorge Lucangeli Obes | 1a122b8 | 2016-11-01 11:59:33 -0400 | [diff] [blame] | 168 | struct bpf_labels *labels, int nr, int grp_idx) |
Jorge Lucangeli Obes | 66cfc14 | 2012-11-30 15:42:52 -0800 | [diff] [blame] | 169 | { |
| 170 | /* Splits the atom. */ |
| 171 | char *atom_ptr; |
| 172 | char *argidx_str = strtok_r(atom, " ", &atom_ptr); |
Jorge Lucangeli Obes | 1a122b8 | 2016-11-01 11:59:33 -0400 | [diff] [blame] | 173 | if (argidx_str == NULL) { |
| 174 | warn("empty atom"); |
| 175 | return -1; |
| 176 | } |
| 177 | |
Jorge Lucangeli Obes | 66cfc14 | 2012-11-30 15:42:52 -0800 | [diff] [blame] | 178 | char *operator_str = strtok_r(NULL, " ", &atom_ptr); |
Jorge Lucangeli Obes | 1a122b8 | 2016-11-01 11:59:33 -0400 | [diff] [blame] | 179 | if (operator_str == NULL) { |
| 180 | warn("invalid atom '%s'", argidx_str); |
| 181 | return -1; |
| 182 | } |
| 183 | |
Jorge Lucangeli Obes | 66cfc14 | 2012-11-30 15:42:52 -0800 | [diff] [blame] | 184 | char *constant_str = strtok_r(NULL, " ", &atom_ptr); |
Jorge Lucangeli Obes | 1a122b8 | 2016-11-01 11:59:33 -0400 | [diff] [blame] | 185 | if (constant_str == NULL) { |
| 186 | warn("invalid atom '%s %s'", argidx_str, operator_str); |
Jorge Lucangeli Obes | 66cfc14 | 2012-11-30 15:42:52 -0800 | [diff] [blame] | 187 | return -1; |
Jorge Lucangeli Obes | 1a122b8 | 2016-11-01 11:59:33 -0400 | [diff] [blame] | 188 | } |
Jorge Lucangeli Obes | 66cfc14 | 2012-11-30 15:42:52 -0800 | [diff] [blame] | 189 | |
Jorge Lucangeli Obes | 1a122b8 | 2016-11-01 11:59:33 -0400 | [diff] [blame] | 190 | /* Checks that there are no extra tokens. */ |
| 191 | const char *extra = strtok_r(NULL, " ", &atom_ptr); |
| 192 | if (extra != NULL) { |
| 193 | warn("extra token '%s'", extra); |
Jorge Lucangeli Obes | 66cfc14 | 2012-11-30 15:42:52 -0800 | [diff] [blame] | 194 | return -1; |
Jorge Lucangeli Obes | 1a122b8 | 2016-11-01 11:59:33 -0400 | [diff] [blame] | 195 | } |
Jorge Lucangeli Obes | 66cfc14 | 2012-11-30 15:42:52 -0800 | [diff] [blame] | 196 | |
| 197 | if (strncmp(argidx_str, "arg", 3)) { |
Jorge Lucangeli Obes | 1a122b8 | 2016-11-01 11:59:33 -0400 | [diff] [blame] | 198 | warn("invalid argument token '%s'", argidx_str); |
Jorge Lucangeli Obes | 66cfc14 | 2012-11-30 15:42:52 -0800 | [diff] [blame] | 199 | return -1; |
| 200 | } |
| 201 | |
| 202 | char *argidx_ptr; |
| 203 | long int argidx = strtol(argidx_str + 3, &argidx_ptr, 10); |
| 204 | /* |
Jorge Lucangeli Obes | 1a122b8 | 2016-11-01 11:59:33 -0400 | [diff] [blame] | 205 | * Checks that an actual argument index was parsed, |
| 206 | * and that there was nothing left after the index. |
Jorge Lucangeli Obes | 66cfc14 | 2012-11-30 15:42:52 -0800 | [diff] [blame] | 207 | */ |
Jorge Lucangeli Obes | 1a122b8 | 2016-11-01 11:59:33 -0400 | [diff] [blame] | 208 | if (argidx_ptr == argidx_str + 3 || *argidx_ptr != '\0') { |
| 209 | warn("invalid argument index '%s'", argidx_str + 3); |
| 210 | return -1; |
| 211 | } |
| 212 | |
| 213 | int op = str_to_op(operator_str); |
| 214 | if (op < MIN_OPERATOR) { |
| 215 | warn("invalid operator '%s'", operator_str); |
Jorge Lucangeli Obes | 66cfc14 | 2012-11-30 15:42:52 -0800 | [diff] [blame] | 216 | return -1; |
Jorge Lucangeli Obes | 5389540 | 2016-10-18 12:02:58 -0400 | [diff] [blame] | 217 | } |
Jorge Lucangeli Obes | 66cfc14 | 2012-11-30 15:42:52 -0800 | [diff] [blame] | 218 | |
Luis Hector Chavez | 40b2574 | 2013-09-22 19:44:06 -0700 | [diff] [blame] | 219 | char *constant_str_ptr; |
| 220 | long int c = parse_constant(constant_str, &constant_str_ptr); |
Jorge Lucangeli Obes | 5389540 | 2016-10-18 12:02:58 -0400 | [diff] [blame] | 221 | if (constant_str_ptr == constant_str) { |
| 222 | warn("invalid constant '%s'", constant_str); |
Luis Hector Chavez | 40b2574 | 2013-09-22 19:44:06 -0700 | [diff] [blame] | 223 | return -1; |
Jorge Lucangeli Obes | 5389540 | 2016-10-18 12:02:58 -0400 | [diff] [blame] | 224 | } |
Luis Hector Chavez | 40b2574 | 2013-09-22 19:44:06 -0700 | [diff] [blame] | 225 | |
Jorge Lucangeli Obes | 66cfc14 | 2012-11-30 15:42:52 -0800 | [diff] [blame] | 226 | /* |
| 227 | * Looks up the label for the end of the AND statement |
| 228 | * this atom belongs to. |
| 229 | */ |
Jorge Lucangeli Obes | 1a122b8 | 2016-11-01 11:59:33 -0400 | [diff] [blame] | 230 | unsigned int id = group_end_lbl(labels, nr, grp_idx); |
Jorge Lucangeli Obes | 66cfc14 | 2012-11-30 15:42:52 -0800 | [diff] [blame] | 231 | |
| 232 | /* |
| 233 | * Builds a BPF comparison between a syscall argument |
| 234 | * and a constant. |
| 235 | * The comparison lives inside an AND statement. |
| 236 | * If the comparison succeeds, we continue |
| 237 | * to the next comparison. |
| 238 | * If this comparison fails, the whole AND statement |
| 239 | * will fail, so we jump to the end of this AND statement. |
| 240 | */ |
| 241 | struct sock_filter *comp_block; |
| 242 | size_t len = bpf_arg_comp(&comp_block, op, argidx, c, id); |
| 243 | if (len == 0) |
| 244 | return -1; |
| 245 | |
| 246 | append_filter_block(head, comp_block, len); |
| 247 | return 0; |
| 248 | } |
| 249 | |
Jorge Lucangeli Obes | 713f6fb | 2016-10-03 13:03:25 -0400 | [diff] [blame] | 250 | 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] | 251 | { |
Jorge Lucangeli Obes | 66cfc14 | 2012-11-30 15:42:52 -0800 | [diff] [blame] | 252 | char *errno_ptr; |
| 253 | |
| 254 | /* Splits the 'return' keyword and the actual errno value. */ |
| 255 | char *ret_str = strtok_r(ret_errno, " ", &errno_ptr); |
| 256 | if (strncmp(ret_str, "return", strlen("return"))) |
| 257 | return -1; |
| 258 | |
| 259 | char *errno_val_str = strtok_r(NULL, " ", &errno_ptr); |
| 260 | |
| 261 | if (errno_val_str) { |
| 262 | char *errno_val_ptr; |
Luis Hector Chavez | 40b2574 | 2013-09-22 19:44:06 -0700 | [diff] [blame] | 263 | int errno_val = parse_constant(errno_val_str, &errno_val_ptr); |
Jorge Lucangeli Obes | 66cfc14 | 2012-11-30 15:42:52 -0800 | [diff] [blame] | 264 | /* Checks to see if we parsed an actual errno. */ |
Jorge Lucangeli Obes | 5389540 | 2016-10-18 12:02:58 -0400 | [diff] [blame] | 265 | if (errno_val_ptr == errno_val_str || errno_val == -1) { |
| 266 | warn("invalid errno value '%s'", errno_val_ptr); |
Jorge Lucangeli Obes | 66cfc14 | 2012-11-30 15:42:52 -0800 | [diff] [blame] | 267 | return -1; |
Jorge Lucangeli Obes | 5389540 | 2016-10-18 12:02:58 -0400 | [diff] [blame] | 268 | } |
Jorge Lucangeli Obes | 66cfc14 | 2012-11-30 15:42:52 -0800 | [diff] [blame] | 269 | |
| 270 | append_ret_errno(head, errno_val); |
| 271 | } else { |
Jorge Lucangeli Obes | 713f6fb | 2016-10-03 13:03:25 -0400 | [diff] [blame] | 272 | if (!use_ret_trap) |
Jennifer Pullman | c0bfae0 | 2016-05-26 17:00:36 -0700 | [diff] [blame] | 273 | append_ret_kill(head); |
| 274 | else |
| 275 | append_ret_trap(head); |
Jorge Lucangeli Obes | 66cfc14 | 2012-11-30 15:42:52 -0800 | [diff] [blame] | 276 | } |
| 277 | return 0; |
| 278 | } |
| 279 | |
Jorge Lucangeli Obes | 45932a5 | 2017-03-15 17:02:58 -0400 | [diff] [blame] | 280 | struct filter_block *compile_policy_line(int nr, const char *policy_line, |
| 281 | unsigned int entry_lbl_id, |
| 282 | struct bpf_labels *labels, |
| 283 | int use_ret_trap) |
Jorge Lucangeli Obes | fc8ab53 | 2012-03-20 10:14:31 -0700 | [diff] [blame] | 284 | { |
| 285 | /* |
| 286 | * |policy_line| should be an expression of the form: |
| 287 | * "arg0 == 3 && arg1 == 5 || arg0 == 0x8" |
| 288 | * |
| 289 | * This is, an expression in DNF (disjunctive normal form); |
| 290 | * a disjunction ('||') of one or more conjunctions ('&&') |
| 291 | * of one or more atoms. |
| 292 | * |
Jorge Lucangeli Obes | d96baf4 | 2013-03-26 15:11:30 -0700 | [diff] [blame] | 293 | * Atoms are of the form "arg{DNUM} {OP} {NUM}" |
Jorge Lucangeli Obes | fc8ab53 | 2012-03-20 10:14:31 -0700 | [diff] [blame] | 294 | * where: |
| 295 | * - DNUM is a decimal number. |
Jorge Lucangeli Obes | 21c3ab1 | 2016-10-12 18:37:37 -0400 | [diff] [blame] | 296 | * - OP is an operator: ==, !=, & (flags set), or 'in' (inclusion). |
Jorge Lucangeli Obes | 66cfc14 | 2012-11-30 15:42:52 -0800 | [diff] [blame] | 297 | * - NUM is an octal, decimal, or hexadecimal number. |
Jorge Lucangeli Obes | fc8ab53 | 2012-03-20 10:14:31 -0700 | [diff] [blame] | 298 | * |
| 299 | * When the syscall arguments make the expression true, |
| 300 | * the syscall is allowed. If not, the process is killed. |
| 301 | * |
Jorge Lucangeli Obes | d96baf4 | 2013-03-26 15:11:30 -0700 | [diff] [blame] | 302 | * To block a syscall without killing the process, |
| 303 | * |policy_line| can be of the form: |
| 304 | * "return <errno>" |
Jorge Lucangeli Obes | fc8ab53 | 2012-03-20 10:14:31 -0700 | [diff] [blame] | 305 | * |
Jorge Lucangeli Obes | d96baf4 | 2013-03-26 15:11:30 -0700 | [diff] [blame] | 306 | * This "return {NUM}" policy line will block the syscall, |
| 307 | * make it return -1 and set |errno| to NUM. |
| 308 | * |
| 309 | * A regular policy line can also include a "return <errno>" clause, |
| 310 | * separated by a semicolon (';'): |
Jorge Lucangeli Obes | fc8ab53 | 2012-03-20 10:14:31 -0700 | [diff] [blame] | 311 | * "arg0 == 3 && arg1 == 5 || arg0 == 0x8; return {NUM}" |
| 312 | * |
Jorge Lucangeli Obes | d96baf4 | 2013-03-26 15:11:30 -0700 | [diff] [blame] | 313 | * If the syscall arguments don't make the expression true, |
| 314 | * 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] | 315 | */ |
| 316 | |
| 317 | size_t len = 0; |
Jorge Lucangeli Obes | 1a122b8 | 2016-11-01 11:59:33 -0400 | [diff] [blame] | 318 | int grp_idx = 0; |
| 319 | |
| 320 | /* Checks for empty policy lines. */ |
| 321 | if (strlen(policy_line) == 0) { |
| 322 | warn("empty policy line"); |
| 323 | return NULL; |
| 324 | } |
Jorge Lucangeli Obes | fc8ab53 | 2012-03-20 10:14:31 -0700 | [diff] [blame] | 325 | |
| 326 | /* Checks for overly long policy lines. */ |
Jorge Lucangeli Obes | bda833c | 2012-07-31 16:25:56 -0700 | [diff] [blame] | 327 | if (strlen(policy_line) >= MAX_POLICY_LINE_LENGTH) |
Jorge Lucangeli Obes | fc8ab53 | 2012-03-20 10:14:31 -0700 | [diff] [blame] | 328 | return NULL; |
| 329 | |
Jorge Lucangeli Obes | d96baf4 | 2013-03-26 15:11:30 -0700 | [diff] [blame] | 330 | /* We will modify |policy_line|, so let's make a copy. */ |
Jorge Lucangeli Obes | bda833c | 2012-07-31 16:25:56 -0700 | [diff] [blame] | 331 | char *line = strndup(policy_line, MAX_POLICY_LINE_LENGTH); |
Jorge Lucangeli Obes | fc8ab53 | 2012-03-20 10:14:31 -0700 | [diff] [blame] | 332 | if (!line) |
| 333 | return NULL; |
| 334 | |
Jorge Lucangeli Obes | fc8ab53 | 2012-03-20 10:14:31 -0700 | [diff] [blame] | 335 | /* |
Jorge Lucangeli Obes | d96baf4 | 2013-03-26 15:11:30 -0700 | [diff] [blame] | 336 | * We build the filter section as a collection of smaller |
Jorge Lucangeli Obes | fc8ab53 | 2012-03-20 10:14:31 -0700 | [diff] [blame] | 337 | * "filter blocks" linked together in a singly-linked list. |
| 338 | */ |
Jorge Lucangeli Obes | d96baf4 | 2013-03-26 15:11:30 -0700 | [diff] [blame] | 339 | struct filter_block *head = new_filter_block(); |
Jorge Lucangeli Obes | fc8ab53 | 2012-03-20 10:14:31 -0700 | [diff] [blame] | 340 | |
| 341 | /* |
Jorge Lucangeli Obes | d96baf4 | 2013-03-26 15:11:30 -0700 | [diff] [blame] | 342 | * Filter sections begin with a label where the main filter |
Jorge Lucangeli Obes | fc8ab53 | 2012-03-20 10:14:31 -0700 | [diff] [blame] | 343 | * will jump after checking the syscall number. |
| 344 | */ |
| 345 | struct sock_filter *entry_label = new_instr_buf(ONE_INSTR); |
| 346 | set_bpf_lbl(entry_label, entry_lbl_id); |
| 347 | append_filter_block(head, entry_label, ONE_INSTR); |
| 348 | |
Jorge Lucangeli Obes | d96baf4 | 2013-03-26 15:11:30 -0700 | [diff] [blame] | 349 | /* Checks whether we're unconditionally blocking this syscall. */ |
| 350 | if (strncmp(line, "return", strlen("return")) == 0) { |
Jorge Lucangeli Obes | 1a122b8 | 2016-11-01 11:59:33 -0400 | [diff] [blame] | 351 | if (compile_errno(head, line, use_ret_trap) < 0) { |
| 352 | free_block_list(head); |
| 353 | free(line); |
Jorge Lucangeli Obes | d96baf4 | 2013-03-26 15:11:30 -0700 | [diff] [blame] | 354 | return NULL; |
Jorge Lucangeli Obes | 1a122b8 | 2016-11-01 11:59:33 -0400 | [diff] [blame] | 355 | } |
Jorge Lucangeli Obes | d96baf4 | 2013-03-26 15:11:30 -0700 | [diff] [blame] | 356 | free(line); |
| 357 | return head; |
| 358 | } |
| 359 | |
| 360 | /* Splits the optional "return <errno>" part. */ |
| 361 | char *line_ptr; |
| 362 | char *arg_filter = strtok_r(line, ";", &line_ptr); |
| 363 | char *ret_errno = strtok_r(NULL, ";", &line_ptr); |
| 364 | |
Jorge Lucangeli Obes | fc8ab53 | 2012-03-20 10:14:31 -0700 | [diff] [blame] | 365 | /* |
| 366 | * Splits the policy line by '||' into conjunctions and each conjunction |
| 367 | * by '&&' into atoms. |
| 368 | */ |
Jorge Lucangeli Obes | 66cfc14 | 2012-11-30 15:42:52 -0800 | [diff] [blame] | 369 | char *arg_filter_str = arg_filter; |
| 370 | char *group; |
| 371 | while ((group = tokenize(&arg_filter_str, "||")) != NULL) { |
| 372 | char *group_str = group; |
| 373 | char *comp; |
| 374 | while ((comp = tokenize(&group_str, "&&")) != NULL) { |
| 375 | /* Compiles each atom into a BPF block. */ |
Jorge Lucangeli Obes | 1a122b8 | 2016-11-01 11:59:33 -0400 | [diff] [blame] | 376 | if (compile_atom(head, comp, labels, nr, grp_idx) < 0) { |
| 377 | free_block_list(head); |
| 378 | free(line); |
Jorge Lucangeli Obes | fc8ab53 | 2012-03-20 10:14:31 -0700 | [diff] [blame] | 379 | return NULL; |
Jorge Lucangeli Obes | 1a122b8 | 2016-11-01 11:59:33 -0400 | [diff] [blame] | 380 | } |
Jorge Lucangeli Obes | fc8ab53 | 2012-03-20 10:14:31 -0700 | [diff] [blame] | 381 | } |
| 382 | /* |
| 383 | * If the AND statement succeeds, we're done, |
| 384 | * so jump to SUCCESS line. |
| 385 | */ |
Jorge Lucangeli Obes | d446726 | 2012-03-23 16:19:59 -0700 | [diff] [blame] | 386 | unsigned int id = success_lbl(labels, nr); |
Jorge Lucangeli Obes | fc8ab53 | 2012-03-20 10:14:31 -0700 | [diff] [blame] | 387 | struct sock_filter *group_end_block = new_instr_buf(TWO_INSTRS); |
| 388 | len = set_bpf_jump_lbl(group_end_block, id); |
| 389 | /* |
| 390 | * The end of each AND statement falls after the |
| 391 | * jump to SUCCESS. |
| 392 | */ |
Jorge Lucangeli Obes | 1a122b8 | 2016-11-01 11:59:33 -0400 | [diff] [blame] | 393 | id = group_end_lbl(labels, nr, grp_idx++); |
Jorge Lucangeli Obes | fc8ab53 | 2012-03-20 10:14:31 -0700 | [diff] [blame] | 394 | len += set_bpf_lbl(group_end_block + len, id); |
| 395 | append_filter_block(head, group_end_block, len); |
| 396 | } |
| 397 | |
| 398 | /* |
| 399 | * If no AND statements succeed, we end up here, |
| 400 | * because we never jumped to SUCCESS. |
| 401 | * If we have to return an errno, do it, |
| 402 | * otherwise just kill the task. |
| 403 | */ |
| 404 | if (ret_errno) { |
Jorge Lucangeli Obes | 1a122b8 | 2016-11-01 11:59:33 -0400 | [diff] [blame] | 405 | if (compile_errno(head, ret_errno, use_ret_trap) < 0) { |
| 406 | free_block_list(head); |
| 407 | free(line); |
Jorge Lucangeli Obes | fc8ab53 | 2012-03-20 10:14:31 -0700 | [diff] [blame] | 408 | return NULL; |
Jorge Lucangeli Obes | 1a122b8 | 2016-11-01 11:59:33 -0400 | [diff] [blame] | 409 | } |
Jorge Lucangeli Obes | fc8ab53 | 2012-03-20 10:14:31 -0700 | [diff] [blame] | 410 | } else { |
Jorge Lucangeli Obes | 713f6fb | 2016-10-03 13:03:25 -0400 | [diff] [blame] | 411 | if (!use_ret_trap) |
Jennifer Pullman | c0bfae0 | 2016-05-26 17:00:36 -0700 | [diff] [blame] | 412 | append_ret_kill(head); |
| 413 | else |
| 414 | append_ret_trap(head); |
Jorge Lucangeli Obes | fc8ab53 | 2012-03-20 10:14:31 -0700 | [diff] [blame] | 415 | } |
| 416 | |
| 417 | /* |
| 418 | * Every time the filter succeeds we jump to a predefined SUCCESS |
| 419 | * label. Add that label and BPF RET_ALLOW code now. |
| 420 | */ |
Jorge Lucangeli Obes | d446726 | 2012-03-23 16:19:59 -0700 | [diff] [blame] | 421 | unsigned int id = success_lbl(labels, nr); |
Jorge Lucangeli Obes | fc8ab53 | 2012-03-20 10:14:31 -0700 | [diff] [blame] | 422 | struct sock_filter *success_block = new_instr_buf(TWO_INSTRS); |
| 423 | len = set_bpf_lbl(success_block, id); |
| 424 | len += set_bpf_ret_allow(success_block + len); |
| 425 | append_filter_block(head, success_block, len); |
| 426 | |
| 427 | free(line); |
| 428 | return head; |
| 429 | } |
| 430 | |
Jorge Lucangeli Obes | 45932a5 | 2017-03-15 17:02:58 -0400 | [diff] [blame] | 431 | int compile_file(FILE *policy_file, struct filter_block *head, |
| 432 | struct filter_block **arg_blocks, struct bpf_labels *labels, |
| 433 | int use_ret_trap, int allow_logging) |
Jorge Lucangeli Obes | d446726 | 2012-03-23 16:19:59 -0700 | [diff] [blame] | 434 | { |
Jorge Lucangeli Obes | 45932a5 | 2017-03-15 17:02:58 -0400 | [diff] [blame] | 435 | /* |
| 436 | * Loop through all the lines in the policy file. |
| 437 | * Build a jump table for the syscall number. |
| 438 | * If the policy line has an arg filter, build the arg filter |
| 439 | * as well. |
| 440 | * Chain the filter sections together and dump them into |
| 441 | * the final buffer at the end. |
| 442 | */ |
| 443 | char *line = NULL; |
| 444 | size_t len = 0; |
| 445 | while (getline(&line, &len, policy_file) != -1) { |
| 446 | char *policy_line = line; |
| 447 | char *syscall_name = strsep(&policy_line, ":"); |
| 448 | int nr = -1; |
Jorge Lucangeli Obes | d446726 | 2012-03-23 16:19:59 -0700 | [diff] [blame] | 449 | |
Jorge Lucangeli Obes | 45932a5 | 2017-03-15 17:02:58 -0400 | [diff] [blame] | 450 | syscall_name = strip(syscall_name); |
| 451 | |
| 452 | /* Allow comments and empty lines. */ |
| 453 | if (*syscall_name == '#' || *syscall_name == '\0') { |
| 454 | /* Reuse |line| in the next getline() call. */ |
| 455 | continue; |
| 456 | } |
| 457 | |
| 458 | policy_line = strip(policy_line); |
| 459 | if (*policy_line == '\0') { |
| 460 | warn("compile_file: empty policy line"); |
| 461 | free(line); |
| 462 | return -1; |
| 463 | } |
| 464 | |
| 465 | nr = lookup_syscall(syscall_name); |
| 466 | if (nr < 0) { |
| 467 | warn("compile_file: nonexistent syscall '%s'", |
| 468 | syscall_name); |
| 469 | if (allow_logging) { |
| 470 | /* |
| 471 | * If we're logging failures, assume we're in a |
| 472 | * debugging case and continue. |
| 473 | * This is not super risky because an invalid |
| 474 | * syscall name is likely caused by a typo or by |
| 475 | * leftover lines from a different architecture. |
| 476 | * In either case, not including a policy line |
| 477 | * is equivalent to killing the process if the |
| 478 | * syscall is made, so there's no added attack |
| 479 | * surface. |
| 480 | */ |
| 481 | /* Reuse |line| in the next getline() call. */ |
| 482 | continue; |
| 483 | } |
| 484 | free(line); |
| 485 | return -1; |
| 486 | } |
| 487 | |
| 488 | /* |
| 489 | * For each syscall, add either a simple ALLOW, |
| 490 | * or an arg filter block. |
| 491 | */ |
| 492 | if (strcmp(policy_line, "1") == 0) { |
| 493 | /* Add simple ALLOW. */ |
| 494 | append_allow_syscall(head, nr); |
| 495 | } else { |
| 496 | /* |
| 497 | * Create and jump to the label that will hold |
| 498 | * the arg filter block. |
| 499 | */ |
| 500 | unsigned int id = bpf_label_id(labels, syscall_name); |
| 501 | struct sock_filter *nr_comp = |
| 502 | new_instr_buf(ALLOW_SYSCALL_LEN); |
| 503 | bpf_allow_syscall_args(nr_comp, nr, id); |
| 504 | append_filter_block(head, nr_comp, ALLOW_SYSCALL_LEN); |
| 505 | |
| 506 | /* Build the arg filter block. */ |
| 507 | struct filter_block *block = compile_policy_line( |
| 508 | nr, policy_line, id, labels, use_ret_trap); |
| 509 | |
| 510 | if (!block) { |
| 511 | if (*arg_blocks) { |
| 512 | free_block_list(*arg_blocks); |
| 513 | } |
| 514 | free(line); |
| 515 | return -1; |
| 516 | } |
| 517 | |
| 518 | if (*arg_blocks) { |
| 519 | extend_filter_block_list(*arg_blocks, block); |
| 520 | } else { |
| 521 | *arg_blocks = block; |
| 522 | } |
| 523 | } |
| 524 | /* Reuse |line| in the next getline() call. */ |
| 525 | } |
| 526 | free(line); |
| 527 | return 0; |
| 528 | } |
| 529 | |
| 530 | int compile_filter(FILE *initial_file, struct sock_fprog *prog, |
| 531 | int use_ret_trap, int allow_logging) |
| 532 | { |
Jorge Lucangeli Obes | d446726 | 2012-03-23 16:19:59 -0700 | [diff] [blame] | 533 | struct bpf_labels labels; |
| 534 | labels.count = 0; |
| 535 | |
Jorge Lucangeli Obes | 45932a5 | 2017-03-15 17:02:58 -0400 | [diff] [blame] | 536 | if (!initial_file) { |
| 537 | warn("compile_filter: |initial_file| is NULL"); |
Jorge Lucangeli Obes | 6135db9 | 2012-07-27 13:37:30 -0700 | [diff] [blame] | 538 | return -1; |
Jorge Lucangeli Obes | 45932a5 | 2017-03-15 17:02:58 -0400 | [diff] [blame] | 539 | } |
Jorge Lucangeli Obes | 6135db9 | 2012-07-27 13:37:30 -0700 | [diff] [blame] | 540 | |
Jorge Lucangeli Obes | d96baf4 | 2013-03-26 15:11:30 -0700 | [diff] [blame] | 541 | struct filter_block *head = new_filter_block(); |
Jorge Lucangeli Obes | d446726 | 2012-03-23 16:19:59 -0700 | [diff] [blame] | 542 | struct filter_block *arg_blocks = NULL; |
| 543 | |
| 544 | /* Start filter by validating arch. */ |
| 545 | struct sock_filter *valid_arch = new_instr_buf(ARCH_VALIDATION_LEN); |
| 546 | size_t len = bpf_validate_arch(valid_arch); |
| 547 | append_filter_block(head, valid_arch, len); |
| 548 | |
Jorge Lucangeli Obes | bda833c | 2012-07-31 16:25:56 -0700 | [diff] [blame] | 549 | /* Load syscall number. */ |
Jorge Lucangeli Obes | d446726 | 2012-03-23 16:19:59 -0700 | [diff] [blame] | 550 | struct sock_filter *load_nr = new_instr_buf(ONE_INSTR); |
| 551 | len = bpf_load_syscall_nr(load_nr); |
| 552 | append_filter_block(head, load_nr, len); |
| 553 | |
Jorge Lucangeli Obes | 713f6fb | 2016-10-03 13:03:25 -0400 | [diff] [blame] | 554 | /* If logging failures, allow the necessary syscalls first. */ |
| 555 | if (allow_logging) |
| 556 | allow_logging_syscalls(head); |
Jorge Lucangeli Obes | bda833c | 2012-07-31 16:25:56 -0700 | [diff] [blame] | 557 | |
Jorge Lucangeli Obes | 45932a5 | 2017-03-15 17:02:58 -0400 | [diff] [blame] | 558 | if (compile_file(initial_file, head, &arg_blocks, &labels, use_ret_trap, |
| 559 | allow_logging) != 0) { |
| 560 | warn("compile_filter: compile_file() failed"); |
| 561 | free_block_list(head); |
| 562 | free_block_list(arg_blocks); |
| 563 | free_label_strings(&labels); |
| 564 | return -1; |
Jorge Lucangeli Obes | d446726 | 2012-03-23 16:19:59 -0700 | [diff] [blame] | 565 | } |
| 566 | |
Jorge Lucangeli Obes | bda833c | 2012-07-31 16:25:56 -0700 | [diff] [blame] | 567 | /* |
Jorge Lucangeli Obes | 713f6fb | 2016-10-03 13:03:25 -0400 | [diff] [blame] | 568 | * If none of the syscalls match, either fall through to KILL, |
Jorge Lucangeli Obes | bda833c | 2012-07-31 16:25:56 -0700 | [diff] [blame] | 569 | * or return TRAP. |
| 570 | */ |
Jorge Lucangeli Obes | 713f6fb | 2016-10-03 13:03:25 -0400 | [diff] [blame] | 571 | if (!use_ret_trap) |
Jorge Lucangeli Obes | bda833c | 2012-07-31 16:25:56 -0700 | [diff] [blame] | 572 | append_ret_kill(head); |
| 573 | else |
| 574 | append_ret_trap(head); |
Jorge Lucangeli Obes | d446726 | 2012-03-23 16:19:59 -0700 | [diff] [blame] | 575 | |
| 576 | /* Allocate the final buffer, now that we know its size. */ |
Jorge Lucangeli Obes | 565e978 | 2016-08-05 11:03:19 -0400 | [diff] [blame] | 577 | size_t final_filter_len = |
| 578 | head->total_len + (arg_blocks ? arg_blocks->total_len : 0); |
Jorge Lucangeli Obes | d446726 | 2012-03-23 16:19:59 -0700 | [diff] [blame] | 579 | if (final_filter_len > BPF_MAXINSNS) |
| 580 | return -1; |
| 581 | |
| 582 | struct sock_filter *final_filter = |
Jorge Lucangeli Obes | 565e978 | 2016-08-05 11:03:19 -0400 | [diff] [blame] | 583 | calloc(final_filter_len, sizeof(struct sock_filter)); |
Jorge Lucangeli Obes | d446726 | 2012-03-23 16:19:59 -0700 | [diff] [blame] | 584 | |
| 585 | if (flatten_block_list(head, final_filter, 0, final_filter_len) < 0) |
| 586 | return -1; |
| 587 | |
Jorge Lucangeli Obes | 565e978 | 2016-08-05 11:03:19 -0400 | [diff] [blame] | 588 | if (flatten_block_list(arg_blocks, final_filter, head->total_len, |
| 589 | final_filter_len) < 0) |
Jorge Lucangeli Obes | d446726 | 2012-03-23 16:19:59 -0700 | [diff] [blame] | 590 | return -1; |
| 591 | |
| 592 | free_block_list(head); |
| 593 | free_block_list(arg_blocks); |
| 594 | |
Jorge Lucangeli Obes | 8cc9d4a | 2016-10-03 10:00:57 -0400 | [diff] [blame] | 595 | if (bpf_resolve_jumps(&labels, final_filter, final_filter_len) < 0) |
| 596 | return -1; |
Jorge Lucangeli Obes | d446726 | 2012-03-23 16:19:59 -0700 | [diff] [blame] | 597 | |
| 598 | free_label_strings(&labels); |
| 599 | |
| 600 | prog->filter = final_filter; |
| 601 | prog->len = final_filter_len; |
| 602 | return 0; |
| 603 | } |
| 604 | |
| 605 | 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] | 606 | size_t index, size_t cap) |
Jorge Lucangeli Obes | d446726 | 2012-03-23 16:19:59 -0700 | [diff] [blame] | 607 | { |
| 608 | size_t _index = index; |
| 609 | |
| 610 | struct filter_block *curr; |
| 611 | size_t i; |
| 612 | |
| 613 | for (curr = head; curr; curr = curr->next) { |
| 614 | for (i = 0; i < curr->len; i++) { |
| 615 | if (_index >= cap) |
| 616 | return -1; |
| 617 | filter[_index++] = curr->instrs[i]; |
| 618 | } |
| 619 | } |
| 620 | return 0; |
| 621 | } |
| 622 | |
Jorge Lucangeli Obes | fc8ab53 | 2012-03-20 10:14:31 -0700 | [diff] [blame] | 623 | void free_block_list(struct filter_block *head) |
| 624 | { |
| 625 | struct filter_block *current, *prev; |
| 626 | |
| 627 | current = head; |
| 628 | while (current) { |
| 629 | free(current->instrs); |
| 630 | prev = current; |
| 631 | current = current->next; |
| 632 | free(prev); |
| 633 | } |
| 634 | } |