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_filter *f = ACCESS_ONCE(current->seccomp.filter); 179 struct seccomp_data sd_local; 180 u32 ret = SECCOMP_RET_ALLOW; 181 182 /* Ensure unexpected behavior doesn't result in failing open. */ 183 if (unlikely(WARN_ON(f == NULL))) 184 return SECCOMP_RET_KILL; 185 186 /* Make sure cross-thread synced filter points somewhere sane. */ 187 smp_read_barrier_depends(); 188 189 if (!sd) { 190 populate_seccomp_data(&sd_local); 191 sd = &sd_local; 192 } 193 194 /* 195 * All filters in the list are evaluated and the lowest BPF return 196 * value always takes priority (ignoring the DATA). 197 */ 198 for (; f; f = f->prev) { 199 u32 cur_ret = BPF_PROG_RUN(f->prog, (void *)sd); 200 201 if ((cur_ret & SECCOMP_RET_ACTION) < (ret & SECCOMP_RET_ACTION)) 202 ret = cur_ret; 203 } 204 return ret; 205 } 206 #endif /* CONFIG_SECCOMP_FILTER */ 207 208 static inline bool seccomp_may_assign_mode(unsigned long seccomp_mode) 209 { 210 assert_spin_locked(¤t->sighand->siglock); 211 212 if (current->seccomp.mode && current->seccomp.mode != seccomp_mode) 213 return false; 214 215 return true; 216 } 217 218 static inline void seccomp_assign_mode(struct task_struct *task, 219 unsigned long seccomp_mode) 220 { 221 assert_spin_locked(&task->sighand->siglock); 222 223 task->seccomp.mode = seccomp_mode; 224 /* 225 * Make sure TIF_SECCOMP cannot be set before the mode (and 226 * filter) is set. 227 */ 228 smp_mb__before_atomic(); 229 set_tsk_thread_flag(task, TIF_SECCOMP); 230 } 231 232 #ifdef CONFIG_SECCOMP_FILTER 233 /* Returns 1 if the parent is an ancestor of the child. */ 234 static int is_ancestor(struct seccomp_filter *parent, 235 struct seccomp_filter *child) 236 { 237 /* NULL is the root ancestor. */ 238 if (parent == NULL) 239 return 1; 240 for (; child; child = child->prev) 241 if (child == parent) 242 return 1; 243 return 0; 244 } 245 246 /** 247 * seccomp_can_sync_threads: checks if all threads can be synchronized 248 * 249 * Expects sighand and cred_guard_mutex locks to be held. 250 * 251 * Returns 0 on success, -ve on error, or the pid of a thread which was 252 * either not in the correct seccomp mode or it did not have an ancestral 253 * seccomp filter. 254 */ 255 static inline pid_t seccomp_can_sync_threads(void) 256 { 257 struct task_struct *thread, *caller; 258 259 BUG_ON(!mutex_is_locked(¤t->signal->cred_guard_mutex)); 260 assert_spin_locked(¤t->sighand->siglock); 261 262 /* Validate all threads being eligible for synchronization. */ 263 caller = current; 264 for_each_thread(caller, thread) { 265 pid_t failed; 266 267 /* Skip current, since it is initiating the sync. */ 268 if (thread == caller) 269 continue; 270 271 if (thread->seccomp.mode == SECCOMP_MODE_DISABLED || 272 (thread->seccomp.mode == SECCOMP_MODE_FILTER && 273 is_ancestor(thread->seccomp.filter, 274 caller->seccomp.filter))) 275 continue; 276 277 /* Return the first thread that cannot be synchronized. */ 278 failed = task_pid_vnr(thread); 279 /* If the pid cannot be resolved, then return -ESRCH */ 280 if (unlikely(WARN_ON(failed == 0))) 281 failed = -ESRCH; 282 return failed; 283 } 284 285 return 0; 286 } 287 288 /** 289 * seccomp_sync_threads: sets all threads to use current's filter 290 * 291 * Expects sighand and cred_guard_mutex locks to be held, and for 292 * seccomp_can_sync_threads() to have returned success already 293 * without dropping the locks. 294 * 295 */ 296 static inline void seccomp_sync_threads(void) 297 { 298 struct task_struct *thread, *caller; 299 300 BUG_ON(!mutex_is_locked(¤t->signal->cred_guard_mutex)); 301 assert_spin_locked(¤t->sighand->siglock); 302 303 /* Synchronize all threads. */ 304 caller = current; 305 for_each_thread(caller, thread) { 306 /* Skip current, since it needs no changes. */ 307 if (thread == caller) 308 continue; 309 310 /* Get a task reference for the new leaf node. */ 311 get_seccomp_filter(caller); 312 /* 313 * Drop the task reference to the shared ancestor since 314 * current's path will hold a reference. (This also 315 * allows a put before the assignment.) 316 */ 317 put_seccomp_filter(thread); 318 smp_store_release(&thread->seccomp.filter, 319 caller->seccomp.filter); 320 /* 321 * Opt the other thread into seccomp if needed. 322 * As threads are considered to be trust-realm 323 * equivalent (see ptrace_may_access), it is safe to 324 * allow one thread to transition the other. 325 */ 326 if (thread->seccomp.mode == SECCOMP_MODE_DISABLED) { 327 /* 328 * Don't let an unprivileged task work around 329 * the no_new_privs restriction by creating 330 * a thread that sets it up, enters seccomp, 331 * then dies. 332 */ 333 if (task_no_new_privs(caller)) 334 task_set_no_new_privs(thread); 335 336 seccomp_assign_mode(thread, SECCOMP_MODE_FILTER); 337 } 338 } 339 } 340 341 /** 342 * seccomp_prepare_filter: Prepares a seccomp filter for use. 343 * @fprog: BPF program to install 344 * 345 * Returns filter on success or an ERR_PTR on failure. 346 */ 347 static struct seccomp_filter *seccomp_prepare_filter(struct sock_fprog *fprog) 348 { 349 struct seccomp_filter *filter; 350 unsigned long fp_size; 351 struct sock_filter *fp; 352 int new_len; 353 long ret; 354 355 if (fprog->len == 0 || fprog->len > BPF_MAXINSNS) 356 return ERR_PTR(-EINVAL); 357 BUG_ON(INT_MAX / fprog->len < sizeof(struct sock_filter)); 358 fp_size = fprog->len * sizeof(struct sock_filter); 359 360 /* 361 * Installing a seccomp filter requires that the task has 362 * CAP_SYS_ADMIN in its namespace or be running with no_new_privs. 363 * This avoids scenarios where unprivileged tasks can affect the 364 * behavior of privileged children. 365 */ 366 if (!task_no_new_privs(current) && 367 security_capable_noaudit(current_cred(), current_user_ns(), 368 CAP_SYS_ADMIN) != 0) 369 return ERR_PTR(-EACCES); 370 371 fp = kzalloc(fp_size, GFP_KERNEL|__GFP_NOWARN); 372 if (!fp) 373 return ERR_PTR(-ENOMEM); 374 375 /* Copy the instructions from fprog. */ 376 ret = -EFAULT; 377 if (copy_from_user(fp, fprog->filter, fp_size)) 378 goto free_prog; 379 380 /* Check and rewrite the fprog via the skb checker */ 381 ret = bpf_check_classic(fp, fprog->len); 382 if (ret) 383 goto free_prog; 384 385 /* Check and rewrite the fprog for seccomp use */ 386 ret = seccomp_check_filter(fp, fprog->len); 387 if (ret) 388 goto free_prog; 389 390 /* Convert 'sock_filter' insns to 'bpf_insn' insns */ 391 ret = bpf_convert_filter(fp, fprog->len, NULL, &new_len); 392 if (ret) 393 goto free_prog; 394 395 /* Allocate a new seccomp_filter */ 396 ret = -ENOMEM; 397 filter = kzalloc(sizeof(struct seccomp_filter), 398 GFP_KERNEL|__GFP_NOWARN); 399 if (!filter) 400 goto free_prog; 401 402 filter->prog = bpf_prog_alloc(bpf_prog_size(new_len), __GFP_NOWARN); 403 if (!filter->prog) 404 goto free_filter; 405 406 ret = bpf_convert_filter(fp, fprog->len, filter->prog->insnsi, &new_len); 407 if (ret) 408 goto free_filter_prog; 409 410 kfree(fp); 411 atomic_set(&filter->usage, 1); 412 filter->prog->len = new_len; 413 414 bpf_prog_select_runtime(filter->prog); 415 416 return filter; 417 418 free_filter_prog: 419 __bpf_prog_free(filter->prog); 420 free_filter: 421 kfree(filter); 422 free_prog: 423 kfree(fp); 424 return ERR_PTR(ret); 425 } 426 427 /** 428 * seccomp_prepare_user_filter - prepares a user-supplied sock_fprog 429 * @user_filter: pointer to the user data containing a sock_fprog. 430 * 431 * Returns 0 on success and non-zero otherwise. 432 */ 433 static struct seccomp_filter * 434 seccomp_prepare_user_filter(const char __user *user_filter) 435 { 436 struct sock_fprog fprog; 437 struct seccomp_filter *filter = ERR_PTR(-EFAULT); 438 439 #ifdef CONFIG_COMPAT 440 if (is_compat_task()) { 441 struct compat_sock_fprog fprog32; 442 if (copy_from_user(&fprog32, user_filter, sizeof(fprog32))) 443 goto out; 444 fprog.len = fprog32.len; 445 fprog.filter = compat_ptr(fprog32.filter); 446 } else /* falls through to the if below. */ 447 #endif 448 if (copy_from_user(&fprog, user_filter, sizeof(fprog))) 449 goto out; 450 filter = seccomp_prepare_filter(&fprog); 451 out: 452 return filter; 453 } 454 455 /** 456 * seccomp_attach_filter: validate and attach filter 457 * @flags: flags to change filter behavior 458 * @filter: seccomp filter to add to the current process 459 * 460 * Caller must be holding current->sighand->siglock lock. 461 * 462 * Returns 0 on success, -ve on error. 463 */ 464 static long seccomp_attach_filter(unsigned int flags, 465 struct seccomp_filter *filter) 466 { 467 unsigned long total_insns; 468 struct seccomp_filter *walker; 469 470 assert_spin_locked(¤t->sighand->siglock); 471 472 /* Validate resulting filter length. */ 473 total_insns = filter->prog->len; 474 for (walker = current->seccomp.filter; walker; walker = walker->prev) 475 total_insns += walker->prog->len + 4; /* 4 instr penalty */ 476 if (total_insns > MAX_INSNS_PER_PATH) 477 return -ENOMEM; 478 479 /* If thread sync has been requested, check that it is possible. */ 480 if (flags & SECCOMP_FILTER_FLAG_TSYNC) { 481 int ret; 482 483 ret = seccomp_can_sync_threads(); 484 if (ret) 485 return ret; 486 } 487 488 /* 489 * If there is an existing filter, make it the prev and don't drop its 490 * task reference. 491 */ 492 filter->prev = current->seccomp.filter; 493 current->seccomp.filter = filter; 494 495 /* Now that the new filter is in place, synchronize to all threads. */ 496 if (flags & SECCOMP_FILTER_FLAG_TSYNC) 497 seccomp_sync_threads(); 498 499 return 0; 500 } 501 502 /* get_seccomp_filter - increments the reference count of the filter on @tsk */ 503 void get_seccomp_filter(struct task_struct *tsk) 504 { 505 struct seccomp_filter *orig = tsk->seccomp.filter; 506 if (!orig) 507 return; 508 /* Reference count is bounded by the number of total processes. */ 509 atomic_inc(&orig->usage); 510 } 511 512 static inline void seccomp_filter_free(struct seccomp_filter *filter) 513 { 514 if (filter) { 515 bpf_prog_free(filter->prog); 516 kfree(filter); 517 } 518 } 519 520 /* put_seccomp_filter - decrements the ref count of tsk->seccomp.filter */ 521 void put_seccomp_filter(struct task_struct *tsk) 522 { 523 struct seccomp_filter *orig = tsk->seccomp.filter; 524 /* Clean up single-reference branches iteratively. */ 525 while (orig && atomic_dec_and_test(&orig->usage)) { 526 struct seccomp_filter *freeme = orig; 527 orig = orig->prev; 528 seccomp_filter_free(freeme); 529 } 530 } 531 532 /** 533 * seccomp_send_sigsys - signals the task to allow in-process syscall emulation 534 * @syscall: syscall number to send to userland 535 * @reason: filter-supplied reason code to send to userland (via si_errno) 536 * 537 * Forces a SIGSYS with a code of SYS_SECCOMP and related sigsys info. 538 */ 539 static void seccomp_send_sigsys(int syscall, int reason) 540 { 541 struct siginfo info; 542 memset(&info, 0, sizeof(info)); 543 info.si_signo = SIGSYS; 544 info.si_code = SYS_SECCOMP; 545 info.si_call_addr = (void __user *)KSTK_EIP(current); 546 info.si_errno = reason; 547 info.si_arch = syscall_get_arch(); 548 info.si_syscall = syscall; 549 force_sig_info(SIGSYS, &info, current); 550 } 551 #endif /* CONFIG_SECCOMP_FILTER */ 552 553 /* 554 * Secure computing mode 1 allows only read/write/exit/sigreturn. 555 * To be fully secure this must be combined with rlimit 556 * to limit the stack allocations too. 557 */ 558 static int mode1_syscalls[] = { 559 __NR_seccomp_read, __NR_seccomp_write, __NR_seccomp_exit, __NR_seccomp_sigreturn, 560 0, /* null terminated */ 561 }; 562 563 #ifdef CONFIG_COMPAT 564 static int mode1_syscalls_32[] = { 565 __NR_seccomp_read_32, __NR_seccomp_write_32, __NR_seccomp_exit_32, __NR_seccomp_sigreturn_32, 566 0, /* null terminated */ 567 }; 568 #endif 569 570 static void __secure_computing_strict(int this_syscall) 571 { 572 int *syscall_whitelist = mode1_syscalls; 573 #ifdef CONFIG_COMPAT 574 if (is_compat_task()) 575 syscall_whitelist = mode1_syscalls_32; 576 #endif 577 do { 578 if (*syscall_whitelist == this_syscall) 579 return; 580 } while (*++syscall_whitelist); 581 582 #ifdef SECCOMP_DEBUG 583 dump_stack(); 584 #endif 585 audit_seccomp(this_syscall, SIGKILL, SECCOMP_RET_KILL); 586 do_exit(SIGKILL); 587 } 588 589 #ifndef CONFIG_HAVE_ARCH_SECCOMP_FILTER 590 void secure_computing_strict(int this_syscall) 591 { 592 int mode = current->seccomp.mode; 593 594 if (mode == 0) 595 return; 596 else if (mode == SECCOMP_MODE_STRICT) 597 __secure_computing_strict(this_syscall); 598 else 599 BUG(); 600 } 601 #else 602 int __secure_computing(void) 603 { 604 u32 phase1_result = seccomp_phase1(NULL); 605 606 if (likely(phase1_result == SECCOMP_PHASE1_OK)) 607 return 0; 608 else if (likely(phase1_result == SECCOMP_PHASE1_SKIP)) 609 return -1; 610 else 611 return seccomp_phase2(phase1_result); 612 } 613 614 #ifdef CONFIG_SECCOMP_FILTER 615 static u32 __seccomp_phase1_filter(int this_syscall, struct seccomp_data *sd) 616 { 617 u32 filter_ret, action; 618 int data; 619 620 /* 621 * Make sure that any changes to mode from another thread have 622 * been seen after TIF_SECCOMP was seen. 623 */ 624 rmb(); 625 626 filter_ret = seccomp_run_filters(sd); 627 data = filter_ret & SECCOMP_RET_DATA; 628 action = filter_ret & SECCOMP_RET_ACTION; 629 630 switch (action) { 631 case SECCOMP_RET_ERRNO: 632 /* Set the low-order 16-bits as a errno. */ 633 syscall_set_return_value(current, task_pt_regs(current), 634 -data, 0); 635 goto skip; 636 637 case SECCOMP_RET_TRAP: 638 /* Show the handler the original registers. */ 639 syscall_rollback(current, task_pt_regs(current)); 640 /* Let the filter pass back 16 bits of data. */ 641 seccomp_send_sigsys(this_syscall, data); 642 goto skip; 643 644 case SECCOMP_RET_TRACE: 645 return filter_ret; /* Save the rest for phase 2. */ 646 647 case SECCOMP_RET_ALLOW: 648 return SECCOMP_PHASE1_OK; 649 650 case SECCOMP_RET_KILL: 651 default: 652 audit_seccomp(this_syscall, SIGSYS, action); 653 do_exit(SIGSYS); 654 } 655 656 unreachable(); 657 658 skip: 659 audit_seccomp(this_syscall, 0, action); 660 return SECCOMP_PHASE1_SKIP; 661 } 662 #endif 663 664 /** 665 * seccomp_phase1() - run fast path seccomp checks on the current syscall 666 * @arg sd: The seccomp_data or NULL 667 * 668 * This only reads pt_regs via the syscall_xyz helpers. The only change 669 * it will make to pt_regs is via syscall_set_return_value, and it will 670 * only do that if it returns SECCOMP_PHASE1_SKIP. 671 * 672 * If sd is provided, it will not read pt_regs at all. 673 * 674 * It may also call do_exit or force a signal; these actions must be 675 * safe. 676 * 677 * If it returns SECCOMP_PHASE1_OK, the syscall passes checks and should 678 * be processed normally. 679 * 680 * If it returns SECCOMP_PHASE1_SKIP, then the syscall should not be 681 * invoked. In this case, seccomp_phase1 will have set the return value 682 * using syscall_set_return_value. 683 * 684 * If it returns anything else, then the return value should be passed 685 * to seccomp_phase2 from a context in which ptrace hooks are safe. 686 */ 687 u32 seccomp_phase1(struct seccomp_data *sd) 688 { 689 int mode = current->seccomp.mode; 690 int this_syscall = sd ? sd->nr : 691 syscall_get_nr(current, task_pt_regs(current)); 692 693 switch (mode) { 694 case SECCOMP_MODE_STRICT: 695 __secure_computing_strict(this_syscall); /* may call do_exit */ 696 return SECCOMP_PHASE1_OK; 697 #ifdef CONFIG_SECCOMP_FILTER 698 case SECCOMP_MODE_FILTER: 699 return __seccomp_phase1_filter(this_syscall, sd); 700 #endif 701 default: 702 BUG(); 703 } 704 } 705 706 /** 707 * seccomp_phase2() - finish slow path seccomp work for the current syscall 708 * @phase1_result: The return value from seccomp_phase1() 709 * 710 * This must be called from a context in which ptrace hooks can be used. 711 * 712 * Returns 0 if the syscall should be processed or -1 to skip the syscall. 713 */ 714 int seccomp_phase2(u32 phase1_result) 715 { 716 struct pt_regs *regs = task_pt_regs(current); 717 u32 action = phase1_result & SECCOMP_RET_ACTION; 718 int data = phase1_result & SECCOMP_RET_DATA; 719 720 BUG_ON(action != SECCOMP_RET_TRACE); 721 722 audit_seccomp(syscall_get_nr(current, regs), 0, action); 723 724 /* Skip these calls if there is no tracer. */ 725 if (!ptrace_event_enabled(current, PTRACE_EVENT_SECCOMP)) { 726 syscall_set_return_value(current, regs, 727 -ENOSYS, 0); 728 return -1; 729 } 730 731 /* Allow the BPF to provide the event message */ 732 ptrace_event(PTRACE_EVENT_SECCOMP, data); 733 /* 734 * The delivery of a fatal signal during event 735 * notification may silently skip tracer notification. 736 * Terminating the task now avoids executing a system 737 * call that may not be intended. 738 */ 739 if (fatal_signal_pending(current)) 740 do_exit(SIGSYS); 741 if (syscall_get_nr(current, regs) < 0) 742 return -1; /* Explicit request to skip. */ 743 744 return 0; 745 } 746 #endif /* CONFIG_HAVE_ARCH_SECCOMP_FILTER */ 747 748 long prctl_get_seccomp(void) 749 { 750 return current->seccomp.mode; 751 } 752 753 /** 754 * seccomp_set_mode_strict: internal function for setting strict seccomp 755 * 756 * Once current->seccomp.mode is non-zero, it may not be changed. 757 * 758 * Returns 0 on success or -EINVAL on failure. 759 */ 760 static long seccomp_set_mode_strict(void) 761 { 762 const unsigned long seccomp_mode = SECCOMP_MODE_STRICT; 763 long ret = -EINVAL; 764 765 spin_lock_irq(¤t->sighand->siglock); 766 767 if (!seccomp_may_assign_mode(seccomp_mode)) 768 goto out; 769 770 #ifdef TIF_NOTSC 771 disable_TSC(); 772 #endif 773 seccomp_assign_mode(current, seccomp_mode); 774 ret = 0; 775 776 out: 777 spin_unlock_irq(¤t->sighand->siglock); 778 779 return ret; 780 } 781 782 #ifdef CONFIG_SECCOMP_FILTER 783 /** 784 * seccomp_set_mode_filter: internal function for setting seccomp filter 785 * @flags: flags to change filter behavior 786 * @filter: struct sock_fprog containing filter 787 * 788 * This function may be called repeatedly to install additional filters. 789 * Every filter successfully installed will be evaluated (in reverse order) 790 * for each system call the task makes. 791 * 792 * Once current->seccomp.mode is non-zero, it may not be changed. 793 * 794 * Returns 0 on success or -EINVAL on failure. 795 */ 796 static long seccomp_set_mode_filter(unsigned int flags, 797 const char __user *filter) 798 { 799 const unsigned long seccomp_mode = SECCOMP_MODE_FILTER; 800 struct seccomp_filter *prepared = NULL; 801 long ret = -EINVAL; 802 803 /* Validate flags. */ 804 if (flags & ~SECCOMP_FILTER_FLAG_MASK) 805 return -EINVAL; 806 807 /* Prepare the new filter before holding any locks. */ 808 prepared = seccomp_prepare_user_filter(filter); 809 if (IS_ERR(prepared)) 810 return PTR_ERR(prepared); 811 812 /* 813 * Make sure we cannot change seccomp or nnp state via TSYNC 814 * while another thread is in the middle of calling exec. 815 */ 816 if (flags & SECCOMP_FILTER_FLAG_TSYNC && 817 mutex_lock_killable(¤t->signal->cred_guard_mutex)) 818 goto out_free; 819 820 spin_lock_irq(¤t->sighand->siglock); 821 822 if (!seccomp_may_assign_mode(seccomp_mode)) 823 goto out; 824 825 ret = seccomp_attach_filter(flags, prepared); 826 if (ret) 827 goto out; 828 /* Do not free the successfully attached filter. */ 829 prepared = NULL; 830 831 seccomp_assign_mode(current, seccomp_mode); 832 out: 833 spin_unlock_irq(¤t->sighand->siglock); 834 if (flags & SECCOMP_FILTER_FLAG_TSYNC) 835 mutex_unlock(¤t->signal->cred_guard_mutex); 836 out_free: 837 seccomp_filter_free(prepared); 838 return ret; 839 } 840 #else 841 static inline long seccomp_set_mode_filter(unsigned int flags, 842 const char __user *filter) 843 { 844 return -EINVAL; 845 } 846 #endif 847 848 /* Common entry point for both prctl and syscall. */ 849 static long do_seccomp(unsigned int op, unsigned int flags, 850 const char __user *uargs) 851 { 852 switch (op) { 853 case SECCOMP_SET_MODE_STRICT: 854 if (flags != 0 || uargs != NULL) 855 return -EINVAL; 856 return seccomp_set_mode_strict(); 857 case SECCOMP_SET_MODE_FILTER: 858 return seccomp_set_mode_filter(flags, uargs); 859 default: 860 return -EINVAL; 861 } 862 } 863 864 SYSCALL_DEFINE3(seccomp, unsigned int, op, unsigned int, flags, 865 const char __user *, uargs) 866 { 867 return do_seccomp(op, flags, uargs); 868 } 869 870 /** 871 * prctl_set_seccomp: configures current->seccomp.mode 872 * @seccomp_mode: requested mode to use 873 * @filter: optional struct sock_fprog for use with SECCOMP_MODE_FILTER 874 * 875 * Returns 0 on success or -EINVAL on failure. 876 */ 877 long prctl_set_seccomp(unsigned long seccomp_mode, char __user *filter) 878 { 879 unsigned int op; 880 char __user *uargs; 881 882 switch (seccomp_mode) { 883 case SECCOMP_MODE_STRICT: 884 op = SECCOMP_SET_MODE_STRICT; 885 /* 886 * Setting strict mode through prctl always ignored filter, 887 * so make sure it is always NULL here to pass the internal 888 * check in do_seccomp(). 889 */ 890 uargs = NULL; 891 break; 892 case SECCOMP_MODE_FILTER: 893 op = SECCOMP_SET_MODE_FILTER; 894 uargs = filter; 895 break; 896 default: 897 return -EINVAL; 898 } 899 900 /* prctl interface doesn't have flags, so they are always zero. */ 901 return do_seccomp(op, 0, uargs); 902 } 903