1 /* 2 * linux/kernel/seccomp.c 3 * 4 * Copyright 2004-2005 Andrea Arcangeli <andrea@cpushare.com> 5 * 6 * Copyright (C) 2012 Google, Inc. 7 * Will Drewry <wad@chromium.org> 8 * 9 * This defines a simple but solid secure-computing facility. 10 * 11 * Mode 1 uses a fixed list of allowed system calls. 12 * Mode 2 allows user-defined system call filters in the form 13 * of Berkeley Packet Filters/Linux Socket Filters. 14 */ 15 16 #include <linux/atomic.h> 17 #include <linux/audit.h> 18 #include <linux/compat.h> 19 #include <linux/sched.h> 20 #include <linux/seccomp.h> 21 #include <linux/slab.h> 22 #include <linux/syscalls.h> 23 24 #ifdef CONFIG_HAVE_ARCH_SECCOMP_FILTER 25 #include <asm/syscall.h> 26 #endif 27 28 #ifdef CONFIG_SECCOMP_FILTER 29 #include <linux/filter.h> 30 #include <linux/pid.h> 31 #include <linux/ptrace.h> 32 #include <linux/security.h> 33 #include <linux/tracehook.h> 34 #include <linux/uaccess.h> 35 36 /** 37 * struct seccomp_filter - container for seccomp BPF programs 38 * 39 * @usage: reference count to manage the object lifetime. 40 * get/put helpers should be used when accessing an instance 41 * outside of a lifetime-guarded section. In general, this 42 * is only needed for handling filters shared across tasks. 43 * @prev: points to a previously installed, or inherited, filter 44 * @len: the number of instructions in the program 45 * @insnsi: the BPF program instructions to evaluate 46 * 47 * seccomp_filter objects are organized in a tree linked via the @prev 48 * pointer. For any task, it appears to be a singly-linked list starting 49 * with current->seccomp.filter, the most recently attached or inherited filter. 50 * However, multiple filters may share a @prev node, by way of fork(), which 51 * results in a unidirectional tree existing in memory. This is similar to 52 * how namespaces work. 53 * 54 * seccomp_filter objects should never be modified after being attached 55 * to a task_struct (other than @usage). 56 */ 57 struct seccomp_filter { 58 atomic_t usage; 59 struct seccomp_filter *prev; 60 struct bpf_prog *prog; 61 }; 62 63 /* Limit any path through the tree to 256KB worth of instructions. */ 64 #define MAX_INSNS_PER_PATH ((1 << 18) / sizeof(struct sock_filter)) 65 66 /* 67 * Endianness is explicitly ignored and left for BPF program authors to manage 68 * as per the specific architecture. 69 */ 70 static void populate_seccomp_data(struct seccomp_data *sd) 71 { 72 struct task_struct *task = current; 73 struct pt_regs *regs = task_pt_regs(task); 74 unsigned long args[6]; 75 76 sd->nr = syscall_get_nr(task, regs); 77 sd->arch = syscall_get_arch(); 78 syscall_get_arguments(task, regs, 0, 6, args); 79 sd->args[0] = args[0]; 80 sd->args[1] = args[1]; 81 sd->args[2] = args[2]; 82 sd->args[3] = args[3]; 83 sd->args[4] = args[4]; 84 sd->args[5] = args[5]; 85 sd->instruction_pointer = KSTK_EIP(task); 86 } 87 88 /** 89 * seccomp_check_filter - verify seccomp filter code 90 * @filter: filter to verify 91 * @flen: length of filter 92 * 93 * Takes a previously checked filter (by bpf_check_classic) and 94 * redirects all filter code that loads struct sk_buff data 95 * and related data through seccomp_bpf_load. It also 96 * enforces length and alignment checking of those loads. 97 * 98 * Returns 0 if the rule set is legal or -EINVAL if not. 99 */ 100 static int seccomp_check_filter(struct sock_filter *filter, unsigned int flen) 101 { 102 int pc; 103 for (pc = 0; pc < flen; pc++) { 104 struct sock_filter *ftest = &filter[pc]; 105 u16 code = ftest->code; 106 u32 k = ftest->k; 107 108 switch (code) { 109 case BPF_LD | BPF_W | BPF_ABS: 110 ftest->code = BPF_LDX | BPF_W | BPF_ABS; 111 /* 32-bit aligned and not out of bounds. */ 112 if (k >= sizeof(struct seccomp_data) || k & 3) 113 return -EINVAL; 114 continue; 115 case BPF_LD | BPF_W | BPF_LEN: 116 ftest->code = BPF_LD | BPF_IMM; 117 ftest->k = sizeof(struct seccomp_data); 118 continue; 119 case BPF_LDX | BPF_W | BPF_LEN: 120 ftest->code = BPF_LDX | BPF_IMM; 121 ftest->k = sizeof(struct seccomp_data); 122 continue; 123 /* Explicitly include allowed calls. */ 124 case BPF_RET | BPF_K: 125 case BPF_RET | BPF_A: 126 case BPF_ALU | BPF_ADD | BPF_K: 127 case BPF_ALU | BPF_ADD | BPF_X: 128 case BPF_ALU | BPF_SUB | BPF_K: 129 case BPF_ALU | BPF_SUB | BPF_X: 130 case BPF_ALU | BPF_MUL | BPF_K: 131 case BPF_ALU | BPF_MUL | BPF_X: 132 case BPF_ALU | BPF_DIV | BPF_K: 133 case BPF_ALU | BPF_DIV | BPF_X: 134 case BPF_ALU | BPF_AND | BPF_K: 135 case BPF_ALU | BPF_AND | BPF_X: 136 case BPF_ALU | BPF_OR | BPF_K: 137 case BPF_ALU | BPF_OR | BPF_X: 138 case BPF_ALU | BPF_XOR | BPF_K: 139 case BPF_ALU | BPF_XOR | BPF_X: 140 case BPF_ALU | BPF_LSH | BPF_K: 141 case BPF_ALU | BPF_LSH | BPF_X: 142 case BPF_ALU | BPF_RSH | BPF_K: 143 case BPF_ALU | BPF_RSH | BPF_X: 144 case BPF_ALU | BPF_NEG: 145 case BPF_LD | BPF_IMM: 146 case BPF_LDX | BPF_IMM: 147 case BPF_MISC | BPF_TAX: 148 case BPF_MISC | BPF_TXA: 149 case BPF_LD | BPF_MEM: 150 case BPF_LDX | BPF_MEM: 151 case BPF_ST: 152 case BPF_STX: 153 case BPF_JMP | BPF_JA: 154 case BPF_JMP | BPF_JEQ | BPF_K: 155 case BPF_JMP | BPF_JEQ | BPF_X: 156 case BPF_JMP | BPF_JGE | BPF_K: 157 case BPF_JMP | BPF_JGE | BPF_X: 158 case BPF_JMP | BPF_JGT | BPF_K: 159 case BPF_JMP | BPF_JGT | BPF_X: 160 case BPF_JMP | BPF_JSET | BPF_K: 161 case BPF_JMP | BPF_JSET | BPF_X: 162 continue; 163 default: 164 return -EINVAL; 165 } 166 } 167 return 0; 168 } 169 170 /** 171 * seccomp_run_filters - evaluates all seccomp filters against @syscall 172 * @syscall: number of the current system call 173 * 174 * Returns valid seccomp BPF response codes. 175 */ 176 static u32 seccomp_run_filters(struct seccomp_data *sd) 177 { 178 struct seccomp_data sd_local; 179 u32 ret = SECCOMP_RET_ALLOW; 180 /* Make sure cross-thread synced filter points somewhere sane. */ 181 struct seccomp_filter *f = 182 lockless_dereference(current->seccomp.filter); 183 184 /* Ensure unexpected behavior doesn't result in failing open. */ 185 if (unlikely(WARN_ON(f == NULL))) 186 return SECCOMP_RET_KILL; 187 188 if (!sd) { 189 populate_seccomp_data(&sd_local); 190 sd = &sd_local; 191 } 192 193 /* 194 * All filters in the list are evaluated and the lowest BPF return 195 * value always takes priority (ignoring the DATA). 196 */ 197 for (; f; f = f->prev) { 198 u32 cur_ret = BPF_PROG_RUN(f->prog, (void *)sd); 199 200 if ((cur_ret & SECCOMP_RET_ACTION) < (ret & SECCOMP_RET_ACTION)) 201 ret = cur_ret; 202 } 203 return ret; 204 } 205 #endif /* CONFIG_SECCOMP_FILTER */ 206 207 static inline bool seccomp_may_assign_mode(unsigned long seccomp_mode) 208 { 209 assert_spin_locked(¤t->sighand->siglock); 210 211 if (current->seccomp.mode && current->seccomp.mode != seccomp_mode) 212 return false; 213 214 return true; 215 } 216 217 static inline void seccomp_assign_mode(struct task_struct *task, 218 unsigned long seccomp_mode) 219 { 220 assert_spin_locked(&task->sighand->siglock); 221 222 task->seccomp.mode = seccomp_mode; 223 /* 224 * Make sure TIF_SECCOMP cannot be set before the mode (and 225 * filter) is set. 226 */ 227 smp_mb__before_atomic(); 228 set_tsk_thread_flag(task, TIF_SECCOMP); 229 } 230 231 #ifdef CONFIG_SECCOMP_FILTER 232 /* Returns 1 if the parent is an ancestor of the child. */ 233 static int is_ancestor(struct seccomp_filter *parent, 234 struct seccomp_filter *child) 235 { 236 /* NULL is the root ancestor. */ 237 if (parent == NULL) 238 return 1; 239 for (; child; child = child->prev) 240 if (child == parent) 241 return 1; 242 return 0; 243 } 244 245 /** 246 * seccomp_can_sync_threads: checks if all threads can be synchronized 247 * 248 * Expects sighand and cred_guard_mutex locks to be held. 249 * 250 * Returns 0 on success, -ve on error, or the pid of a thread which was 251 * either not in the correct seccomp mode or it did not have an ancestral 252 * seccomp filter. 253 */ 254 static inline pid_t seccomp_can_sync_threads(void) 255 { 256 struct task_struct *thread, *caller; 257 258 BUG_ON(!mutex_is_locked(¤t->signal->cred_guard_mutex)); 259 assert_spin_locked(¤t->sighand->siglock); 260 261 /* Validate all threads being eligible for synchronization. */ 262 caller = current; 263 for_each_thread(caller, thread) { 264 pid_t failed; 265 266 /* Skip current, since it is initiating the sync. */ 267 if (thread == caller) 268 continue; 269 270 if (thread->seccomp.mode == SECCOMP_MODE_DISABLED || 271 (thread->seccomp.mode == SECCOMP_MODE_FILTER && 272 is_ancestor(thread->seccomp.filter, 273 caller->seccomp.filter))) 274 continue; 275 276 /* Return the first thread that cannot be synchronized. */ 277 failed = task_pid_vnr(thread); 278 /* If the pid cannot be resolved, then return -ESRCH */ 279 if (unlikely(WARN_ON(failed == 0))) 280 failed = -ESRCH; 281 return failed; 282 } 283 284 return 0; 285 } 286 287 /** 288 * seccomp_sync_threads: sets all threads to use current's filter 289 * 290 * Expects sighand and cred_guard_mutex locks to be held, and for 291 * seccomp_can_sync_threads() to have returned success already 292 * without dropping the locks. 293 * 294 */ 295 static inline void seccomp_sync_threads(void) 296 { 297 struct task_struct *thread, *caller; 298 299 BUG_ON(!mutex_is_locked(¤t->signal->cred_guard_mutex)); 300 assert_spin_locked(¤t->sighand->siglock); 301 302 /* Synchronize all threads. */ 303 caller = current; 304 for_each_thread(caller, thread) { 305 /* Skip current, since it needs no changes. */ 306 if (thread == caller) 307 continue; 308 309 /* Get a task reference for the new leaf node. */ 310 get_seccomp_filter(caller); 311 /* 312 * Drop the task reference to the shared ancestor since 313 * current's path will hold a reference. (This also 314 * allows a put before the assignment.) 315 */ 316 put_seccomp_filter(thread); 317 smp_store_release(&thread->seccomp.filter, 318 caller->seccomp.filter); 319 /* 320 * Opt the other thread into seccomp if needed. 321 * As threads are considered to be trust-realm 322 * equivalent (see ptrace_may_access), it is safe to 323 * allow one thread to transition the other. 324 */ 325 if (thread->seccomp.mode == SECCOMP_MODE_DISABLED) { 326 /* 327 * Don't let an unprivileged task work around 328 * the no_new_privs restriction by creating 329 * a thread that sets it up, enters seccomp, 330 * then dies. 331 */ 332 if (task_no_new_privs(caller)) 333 task_set_no_new_privs(thread); 334 335 seccomp_assign_mode(thread, SECCOMP_MODE_FILTER); 336 } 337 } 338 } 339 340 /** 341 * seccomp_prepare_filter: Prepares a seccomp filter for use. 342 * @fprog: BPF program to install 343 * 344 * Returns filter on success or an ERR_PTR on failure. 345 */ 346 static struct seccomp_filter *seccomp_prepare_filter(struct sock_fprog *fprog) 347 { 348 struct seccomp_filter *sfilter; 349 int ret; 350 351 if (fprog->len == 0 || fprog->len > BPF_MAXINSNS) 352 return ERR_PTR(-EINVAL); 353 354 BUG_ON(INT_MAX / fprog->len < sizeof(struct sock_filter)); 355 356 /* 357 * Installing a seccomp filter requires that the task has 358 * CAP_SYS_ADMIN in its namespace or be running with no_new_privs. 359 * This avoids scenarios where unprivileged tasks can affect the 360 * behavior of privileged children. 361 */ 362 if (!task_no_new_privs(current) && 363 security_capable_noaudit(current_cred(), current_user_ns(), 364 CAP_SYS_ADMIN) != 0) 365 return ERR_PTR(-EACCES); 366 367 /* Allocate a new seccomp_filter */ 368 sfilter = kzalloc(sizeof(*sfilter), GFP_KERNEL | __GFP_NOWARN); 369 if (!sfilter) 370 return ERR_PTR(-ENOMEM); 371 372 ret = bpf_prog_create_from_user(&sfilter->prog, fprog, 373 seccomp_check_filter); 374 if (ret < 0) { 375 kfree(sfilter); 376 return ERR_PTR(ret); 377 } 378 379 atomic_set(&sfilter->usage, 1); 380 381 return sfilter; 382 } 383 384 /** 385 * seccomp_prepare_user_filter - prepares a user-supplied sock_fprog 386 * @user_filter: pointer to the user data containing a sock_fprog. 387 * 388 * Returns 0 on success and non-zero otherwise. 389 */ 390 static struct seccomp_filter * 391 seccomp_prepare_user_filter(const char __user *user_filter) 392 { 393 struct sock_fprog fprog; 394 struct seccomp_filter *filter = ERR_PTR(-EFAULT); 395 396 #ifdef CONFIG_COMPAT 397 if (is_compat_task()) { 398 struct compat_sock_fprog fprog32; 399 if (copy_from_user(&fprog32, user_filter, sizeof(fprog32))) 400 goto out; 401 fprog.len = fprog32.len; 402 fprog.filter = compat_ptr(fprog32.filter); 403 } else /* falls through to the if below. */ 404 #endif 405 if (copy_from_user(&fprog, user_filter, sizeof(fprog))) 406 goto out; 407 filter = seccomp_prepare_filter(&fprog); 408 out: 409 return filter; 410 } 411 412 /** 413 * seccomp_attach_filter: validate and attach filter 414 * @flags: flags to change filter behavior 415 * @filter: seccomp filter to add to the current process 416 * 417 * Caller must be holding current->sighand->siglock lock. 418 * 419 * Returns 0 on success, -ve on error. 420 */ 421 static long seccomp_attach_filter(unsigned int flags, 422 struct seccomp_filter *filter) 423 { 424 unsigned long total_insns; 425 struct seccomp_filter *walker; 426 427 assert_spin_locked(¤t->sighand->siglock); 428 429 /* Validate resulting filter length. */ 430 total_insns = filter->prog->len; 431 for (walker = current->seccomp.filter; walker; walker = walker->prev) 432 total_insns += walker->prog->len + 4; /* 4 instr penalty */ 433 if (total_insns > MAX_INSNS_PER_PATH) 434 return -ENOMEM; 435 436 /* If thread sync has been requested, check that it is possible. */ 437 if (flags & SECCOMP_FILTER_FLAG_TSYNC) { 438 int ret; 439 440 ret = seccomp_can_sync_threads(); 441 if (ret) 442 return ret; 443 } 444 445 /* 446 * If there is an existing filter, make it the prev and don't drop its 447 * task reference. 448 */ 449 filter->prev = current->seccomp.filter; 450 current->seccomp.filter = filter; 451 452 /* Now that the new filter is in place, synchronize to all threads. */ 453 if (flags & SECCOMP_FILTER_FLAG_TSYNC) 454 seccomp_sync_threads(); 455 456 return 0; 457 } 458 459 /* get_seccomp_filter - increments the reference count of the filter on @tsk */ 460 void get_seccomp_filter(struct task_struct *tsk) 461 { 462 struct seccomp_filter *orig = tsk->seccomp.filter; 463 if (!orig) 464 return; 465 /* Reference count is bounded by the number of total processes. */ 466 atomic_inc(&orig->usage); 467 } 468 469 static inline void seccomp_filter_free(struct seccomp_filter *filter) 470 { 471 if (filter) { 472 bpf_prog_free(filter->prog); 473 kfree(filter); 474 } 475 } 476 477 /* put_seccomp_filter - decrements the ref count of tsk->seccomp.filter */ 478 void put_seccomp_filter(struct task_struct *tsk) 479 { 480 struct seccomp_filter *orig = tsk->seccomp.filter; 481 /* Clean up single-reference branches iteratively. */ 482 while (orig && atomic_dec_and_test(&orig->usage)) { 483 struct seccomp_filter *freeme = orig; 484 orig = orig->prev; 485 seccomp_filter_free(freeme); 486 } 487 } 488 489 /** 490 * seccomp_send_sigsys - signals the task to allow in-process syscall emulation 491 * @syscall: syscall number to send to userland 492 * @reason: filter-supplied reason code to send to userland (via si_errno) 493 * 494 * Forces a SIGSYS with a code of SYS_SECCOMP and related sigsys info. 495 */ 496 static void seccomp_send_sigsys(int syscall, int reason) 497 { 498 struct siginfo info; 499 memset(&info, 0, sizeof(info)); 500 info.si_signo = SIGSYS; 501 info.si_code = SYS_SECCOMP; 502 info.si_call_addr = (void __user *)KSTK_EIP(current); 503 info.si_errno = reason; 504 info.si_arch = syscall_get_arch(); 505 info.si_syscall = syscall; 506 force_sig_info(SIGSYS, &info, current); 507 } 508 #endif /* CONFIG_SECCOMP_FILTER */ 509 510 /* 511 * Secure computing mode 1 allows only read/write/exit/sigreturn. 512 * To be fully secure this must be combined with rlimit 513 * to limit the stack allocations too. 514 */ 515 static int mode1_syscalls[] = { 516 __NR_seccomp_read, __NR_seccomp_write, __NR_seccomp_exit, __NR_seccomp_sigreturn, 517 0, /* null terminated */ 518 }; 519 520 #ifdef CONFIG_COMPAT 521 static int mode1_syscalls_32[] = { 522 __NR_seccomp_read_32, __NR_seccomp_write_32, __NR_seccomp_exit_32, __NR_seccomp_sigreturn_32, 523 0, /* null terminated */ 524 }; 525 #endif 526 527 static void __secure_computing_strict(int this_syscall) 528 { 529 int *syscall_whitelist = mode1_syscalls; 530 #ifdef CONFIG_COMPAT 531 if (is_compat_task()) 532 syscall_whitelist = mode1_syscalls_32; 533 #endif 534 do { 535 if (*syscall_whitelist == this_syscall) 536 return; 537 } while (*++syscall_whitelist); 538 539 #ifdef SECCOMP_DEBUG 540 dump_stack(); 541 #endif 542 audit_seccomp(this_syscall, SIGKILL, SECCOMP_RET_KILL); 543 do_exit(SIGKILL); 544 } 545 546 #ifndef CONFIG_HAVE_ARCH_SECCOMP_FILTER 547 void secure_computing_strict(int this_syscall) 548 { 549 int mode = current->seccomp.mode; 550 551 if (config_enabled(CONFIG_CHECKPOINT_RESTORE) && 552 unlikely(current->ptrace & PT_SUSPEND_SECCOMP)) 553 return; 554 555 if (mode == SECCOMP_MODE_DISABLED) 556 return; 557 else if (mode == SECCOMP_MODE_STRICT) 558 __secure_computing_strict(this_syscall); 559 else 560 BUG(); 561 } 562 #else 563 int __secure_computing(void) 564 { 565 u32 phase1_result = seccomp_phase1(NULL); 566 567 if (likely(phase1_result == SECCOMP_PHASE1_OK)) 568 return 0; 569 else if (likely(phase1_result == SECCOMP_PHASE1_SKIP)) 570 return -1; 571 else 572 return seccomp_phase2(phase1_result); 573 } 574 575 #ifdef CONFIG_SECCOMP_FILTER 576 static u32 __seccomp_phase1_filter(int this_syscall, struct seccomp_data *sd) 577 { 578 u32 filter_ret, action; 579 int data; 580 581 /* 582 * Make sure that any changes to mode from another thread have 583 * been seen after TIF_SECCOMP was seen. 584 */ 585 rmb(); 586 587 filter_ret = seccomp_run_filters(sd); 588 data = filter_ret & SECCOMP_RET_DATA; 589 action = filter_ret & SECCOMP_RET_ACTION; 590 591 switch (action) { 592 case SECCOMP_RET_ERRNO: 593 /* Set low-order bits as an errno, capped at MAX_ERRNO. */ 594 if (data > MAX_ERRNO) 595 data = MAX_ERRNO; 596 syscall_set_return_value(current, task_pt_regs(current), 597 -data, 0); 598 goto skip; 599 600 case SECCOMP_RET_TRAP: 601 /* Show the handler the original registers. */ 602 syscall_rollback(current, task_pt_regs(current)); 603 /* Let the filter pass back 16 bits of data. */ 604 seccomp_send_sigsys(this_syscall, data); 605 goto skip; 606 607 case SECCOMP_RET_TRACE: 608 return filter_ret; /* Save the rest for phase 2. */ 609 610 case SECCOMP_RET_ALLOW: 611 return SECCOMP_PHASE1_OK; 612 613 case SECCOMP_RET_KILL: 614 default: 615 audit_seccomp(this_syscall, SIGSYS, action); 616 do_exit(SIGSYS); 617 } 618 619 unreachable(); 620 621 skip: 622 audit_seccomp(this_syscall, 0, action); 623 return SECCOMP_PHASE1_SKIP; 624 } 625 #endif 626 627 /** 628 * seccomp_phase1() - run fast path seccomp checks on the current syscall 629 * @arg sd: The seccomp_data or NULL 630 * 631 * This only reads pt_regs via the syscall_xyz helpers. The only change 632 * it will make to pt_regs is via syscall_set_return_value, and it will 633 * only do that if it returns SECCOMP_PHASE1_SKIP. 634 * 635 * If sd is provided, it will not read pt_regs at all. 636 * 637 * It may also call do_exit or force a signal; these actions must be 638 * safe. 639 * 640 * If it returns SECCOMP_PHASE1_OK, the syscall passes checks and should 641 * be processed normally. 642 * 643 * If it returns SECCOMP_PHASE1_SKIP, then the syscall should not be 644 * invoked. In this case, seccomp_phase1 will have set the return value 645 * using syscall_set_return_value. 646 * 647 * If it returns anything else, then the return value should be passed 648 * to seccomp_phase2 from a context in which ptrace hooks are safe. 649 */ 650 u32 seccomp_phase1(struct seccomp_data *sd) 651 { 652 int mode = current->seccomp.mode; 653 int this_syscall = sd ? sd->nr : 654 syscall_get_nr(current, task_pt_regs(current)); 655 656 if (config_enabled(CONFIG_CHECKPOINT_RESTORE) && 657 unlikely(current->ptrace & PT_SUSPEND_SECCOMP)) 658 return SECCOMP_PHASE1_OK; 659 660 switch (mode) { 661 case SECCOMP_MODE_STRICT: 662 __secure_computing_strict(this_syscall); /* may call do_exit */ 663 return SECCOMP_PHASE1_OK; 664 #ifdef CONFIG_SECCOMP_FILTER 665 case SECCOMP_MODE_FILTER: 666 return __seccomp_phase1_filter(this_syscall, sd); 667 #endif 668 default: 669 BUG(); 670 } 671 } 672 673 /** 674 * seccomp_phase2() - finish slow path seccomp work for the current syscall 675 * @phase1_result: The return value from seccomp_phase1() 676 * 677 * This must be called from a context in which ptrace hooks can be used. 678 * 679 * Returns 0 if the syscall should be processed or -1 to skip the syscall. 680 */ 681 int seccomp_phase2(u32 phase1_result) 682 { 683 struct pt_regs *regs = task_pt_regs(current); 684 u32 action = phase1_result & SECCOMP_RET_ACTION; 685 int data = phase1_result & SECCOMP_RET_DATA; 686 687 BUG_ON(action != SECCOMP_RET_TRACE); 688 689 audit_seccomp(syscall_get_nr(current, regs), 0, action); 690 691 /* Skip these calls if there is no tracer. */ 692 if (!ptrace_event_enabled(current, PTRACE_EVENT_SECCOMP)) { 693 syscall_set_return_value(current, regs, 694 -ENOSYS, 0); 695 return -1; 696 } 697 698 /* Allow the BPF to provide the event message */ 699 ptrace_event(PTRACE_EVENT_SECCOMP, data); 700 /* 701 * The delivery of a fatal signal during event 702 * notification may silently skip tracer notification. 703 * Terminating the task now avoids executing a system 704 * call that may not be intended. 705 */ 706 if (fatal_signal_pending(current)) 707 do_exit(SIGSYS); 708 if (syscall_get_nr(current, regs) < 0) 709 return -1; /* Explicit request to skip. */ 710 711 return 0; 712 } 713 #endif /* CONFIG_HAVE_ARCH_SECCOMP_FILTER */ 714 715 long prctl_get_seccomp(void) 716 { 717 return current->seccomp.mode; 718 } 719 720 /** 721 * seccomp_set_mode_strict: internal function for setting strict seccomp 722 * 723 * Once current->seccomp.mode is non-zero, it may not be changed. 724 * 725 * Returns 0 on success or -EINVAL on failure. 726 */ 727 static long seccomp_set_mode_strict(void) 728 { 729 const unsigned long seccomp_mode = SECCOMP_MODE_STRICT; 730 long ret = -EINVAL; 731 732 spin_lock_irq(¤t->sighand->siglock); 733 734 if (!seccomp_may_assign_mode(seccomp_mode)) 735 goto out; 736 737 #ifdef TIF_NOTSC 738 disable_TSC(); 739 #endif 740 seccomp_assign_mode(current, seccomp_mode); 741 ret = 0; 742 743 out: 744 spin_unlock_irq(¤t->sighand->siglock); 745 746 return ret; 747 } 748 749 #ifdef CONFIG_SECCOMP_FILTER 750 /** 751 * seccomp_set_mode_filter: internal function for setting seccomp filter 752 * @flags: flags to change filter behavior 753 * @filter: struct sock_fprog containing filter 754 * 755 * This function may be called repeatedly to install additional filters. 756 * Every filter successfully installed will be evaluated (in reverse order) 757 * for each system call the task makes. 758 * 759 * Once current->seccomp.mode is non-zero, it may not be changed. 760 * 761 * Returns 0 on success or -EINVAL on failure. 762 */ 763 static long seccomp_set_mode_filter(unsigned int flags, 764 const char __user *filter) 765 { 766 const unsigned long seccomp_mode = SECCOMP_MODE_FILTER; 767 struct seccomp_filter *prepared = NULL; 768 long ret = -EINVAL; 769 770 /* Validate flags. */ 771 if (flags & ~SECCOMP_FILTER_FLAG_MASK) 772 return -EINVAL; 773 774 /* Prepare the new filter before holding any locks. */ 775 prepared = seccomp_prepare_user_filter(filter); 776 if (IS_ERR(prepared)) 777 return PTR_ERR(prepared); 778 779 /* 780 * Make sure we cannot change seccomp or nnp state via TSYNC 781 * while another thread is in the middle of calling exec. 782 */ 783 if (flags & SECCOMP_FILTER_FLAG_TSYNC && 784 mutex_lock_killable(¤t->signal->cred_guard_mutex)) 785 goto out_free; 786 787 spin_lock_irq(¤t->sighand->siglock); 788 789 if (!seccomp_may_assign_mode(seccomp_mode)) 790 goto out; 791 792 ret = seccomp_attach_filter(flags, prepared); 793 if (ret) 794 goto out; 795 /* Do not free the successfully attached filter. */ 796 prepared = NULL; 797 798 seccomp_assign_mode(current, seccomp_mode); 799 out: 800 spin_unlock_irq(¤t->sighand->siglock); 801 if (flags & SECCOMP_FILTER_FLAG_TSYNC) 802 mutex_unlock(¤t->signal->cred_guard_mutex); 803 out_free: 804 seccomp_filter_free(prepared); 805 return ret; 806 } 807 #else 808 static inline long seccomp_set_mode_filter(unsigned int flags, 809 const char __user *filter) 810 { 811 return -EINVAL; 812 } 813 #endif 814 815 /* Common entry point for both prctl and syscall. */ 816 static long do_seccomp(unsigned int op, unsigned int flags, 817 const char __user *uargs) 818 { 819 switch (op) { 820 case SECCOMP_SET_MODE_STRICT: 821 if (flags != 0 || uargs != NULL) 822 return -EINVAL; 823 return seccomp_set_mode_strict(); 824 case SECCOMP_SET_MODE_FILTER: 825 return seccomp_set_mode_filter(flags, uargs); 826 default: 827 return -EINVAL; 828 } 829 } 830 831 SYSCALL_DEFINE3(seccomp, unsigned int, op, unsigned int, flags, 832 const char __user *, uargs) 833 { 834 return do_seccomp(op, flags, uargs); 835 } 836 837 /** 838 * prctl_set_seccomp: configures current->seccomp.mode 839 * @seccomp_mode: requested mode to use 840 * @filter: optional struct sock_fprog for use with SECCOMP_MODE_FILTER 841 * 842 * Returns 0 on success or -EINVAL on failure. 843 */ 844 long prctl_set_seccomp(unsigned long seccomp_mode, char __user *filter) 845 { 846 unsigned int op; 847 char __user *uargs; 848 849 switch (seccomp_mode) { 850 case SECCOMP_MODE_STRICT: 851 op = SECCOMP_SET_MODE_STRICT; 852 /* 853 * Setting strict mode through prctl always ignored filter, 854 * so make sure it is always NULL here to pass the internal 855 * check in do_seccomp(). 856 */ 857 uargs = NULL; 858 break; 859 case SECCOMP_MODE_FILTER: 860 op = SECCOMP_SET_MODE_FILTER; 861 uargs = filter; 862 break; 863 default: 864 return -EINVAL; 865 } 866 867 /* prctl interface doesn't have flags, so they are always zero. */ 868 return do_seccomp(op, 0, uargs); 869 } 870