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 /* 321 * Don't let an unprivileged task work around 322 * the no_new_privs restriction by creating 323 * a thread that sets it up, enters seccomp, 324 * then dies. 325 */ 326 if (task_no_new_privs(caller)) 327 task_set_no_new_privs(thread); 328 329 /* 330 * Opt the other thread into seccomp if needed. 331 * As threads are considered to be trust-realm 332 * equivalent (see ptrace_may_access), it is safe to 333 * allow one thread to transition the other. 334 */ 335 if (thread->seccomp.mode == SECCOMP_MODE_DISABLED) 336 seccomp_assign_mode(thread, SECCOMP_MODE_FILTER); 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 const bool save_orig = config_enabled(CONFIG_CHECKPOINT_RESTORE); 351 352 if (fprog->len == 0 || fprog->len > BPF_MAXINSNS) 353 return ERR_PTR(-EINVAL); 354 355 BUG_ON(INT_MAX / fprog->len < sizeof(struct sock_filter)); 356 357 /* 358 * Installing a seccomp filter requires that the task has 359 * CAP_SYS_ADMIN in its namespace or be running with no_new_privs. 360 * This avoids scenarios where unprivileged tasks can affect the 361 * behavior of privileged children. 362 */ 363 if (!task_no_new_privs(current) && 364 security_capable_noaudit(current_cred(), current_user_ns(), 365 CAP_SYS_ADMIN) != 0) 366 return ERR_PTR(-EACCES); 367 368 /* Allocate a new seccomp_filter */ 369 sfilter = kzalloc(sizeof(*sfilter), GFP_KERNEL | __GFP_NOWARN); 370 if (!sfilter) 371 return ERR_PTR(-ENOMEM); 372 373 ret = bpf_prog_create_from_user(&sfilter->prog, fprog, 374 seccomp_check_filter, save_orig); 375 if (ret < 0) { 376 kfree(sfilter); 377 return ERR_PTR(ret); 378 } 379 380 atomic_set(&sfilter->usage, 1); 381 382 return sfilter; 383 } 384 385 /** 386 * seccomp_prepare_user_filter - prepares a user-supplied sock_fprog 387 * @user_filter: pointer to the user data containing a sock_fprog. 388 * 389 * Returns 0 on success and non-zero otherwise. 390 */ 391 static struct seccomp_filter * 392 seccomp_prepare_user_filter(const char __user *user_filter) 393 { 394 struct sock_fprog fprog; 395 struct seccomp_filter *filter = ERR_PTR(-EFAULT); 396 397 #ifdef CONFIG_COMPAT 398 if (in_compat_syscall()) { 399 struct compat_sock_fprog fprog32; 400 if (copy_from_user(&fprog32, user_filter, sizeof(fprog32))) 401 goto out; 402 fprog.len = fprog32.len; 403 fprog.filter = compat_ptr(fprog32.filter); 404 } else /* falls through to the if below. */ 405 #endif 406 if (copy_from_user(&fprog, user_filter, sizeof(fprog))) 407 goto out; 408 filter = seccomp_prepare_filter(&fprog); 409 out: 410 return filter; 411 } 412 413 /** 414 * seccomp_attach_filter: validate and attach filter 415 * @flags: flags to change filter behavior 416 * @filter: seccomp filter to add to the current process 417 * 418 * Caller must be holding current->sighand->siglock lock. 419 * 420 * Returns 0 on success, -ve on error. 421 */ 422 static long seccomp_attach_filter(unsigned int flags, 423 struct seccomp_filter *filter) 424 { 425 unsigned long total_insns; 426 struct seccomp_filter *walker; 427 428 assert_spin_locked(¤t->sighand->siglock); 429 430 /* Validate resulting filter length. */ 431 total_insns = filter->prog->len; 432 for (walker = current->seccomp.filter; walker; walker = walker->prev) 433 total_insns += walker->prog->len + 4; /* 4 instr penalty */ 434 if (total_insns > MAX_INSNS_PER_PATH) 435 return -ENOMEM; 436 437 /* If thread sync has been requested, check that it is possible. */ 438 if (flags & SECCOMP_FILTER_FLAG_TSYNC) { 439 int ret; 440 441 ret = seccomp_can_sync_threads(); 442 if (ret) 443 return ret; 444 } 445 446 /* 447 * If there is an existing filter, make it the prev and don't drop its 448 * task reference. 449 */ 450 filter->prev = current->seccomp.filter; 451 current->seccomp.filter = filter; 452 453 /* Now that the new filter is in place, synchronize to all threads. */ 454 if (flags & SECCOMP_FILTER_FLAG_TSYNC) 455 seccomp_sync_threads(); 456 457 return 0; 458 } 459 460 /* get_seccomp_filter - increments the reference count of the filter on @tsk */ 461 void get_seccomp_filter(struct task_struct *tsk) 462 { 463 struct seccomp_filter *orig = tsk->seccomp.filter; 464 if (!orig) 465 return; 466 /* Reference count is bounded by the number of total processes. */ 467 atomic_inc(&orig->usage); 468 } 469 470 static inline void seccomp_filter_free(struct seccomp_filter *filter) 471 { 472 if (filter) { 473 bpf_prog_destroy(filter->prog); 474 kfree(filter); 475 } 476 } 477 478 /* put_seccomp_filter - decrements the ref count of tsk->seccomp.filter */ 479 void put_seccomp_filter(struct task_struct *tsk) 480 { 481 struct seccomp_filter *orig = tsk->seccomp.filter; 482 /* Clean up single-reference branches iteratively. */ 483 while (orig && atomic_dec_and_test(&orig->usage)) { 484 struct seccomp_filter *freeme = orig; 485 orig = orig->prev; 486 seccomp_filter_free(freeme); 487 } 488 } 489 490 /** 491 * seccomp_send_sigsys - signals the task to allow in-process syscall emulation 492 * @syscall: syscall number to send to userland 493 * @reason: filter-supplied reason code to send to userland (via si_errno) 494 * 495 * Forces a SIGSYS with a code of SYS_SECCOMP and related sigsys info. 496 */ 497 static void seccomp_send_sigsys(int syscall, int reason) 498 { 499 struct siginfo info; 500 memset(&info, 0, sizeof(info)); 501 info.si_signo = SIGSYS; 502 info.si_code = SYS_SECCOMP; 503 info.si_call_addr = (void __user *)KSTK_EIP(current); 504 info.si_errno = reason; 505 info.si_arch = syscall_get_arch(); 506 info.si_syscall = syscall; 507 force_sig_info(SIGSYS, &info, current); 508 } 509 #endif /* CONFIG_SECCOMP_FILTER */ 510 511 /* 512 * Secure computing mode 1 allows only read/write/exit/sigreturn. 513 * To be fully secure this must be combined with rlimit 514 * to limit the stack allocations too. 515 */ 516 static int mode1_syscalls[] = { 517 __NR_seccomp_read, __NR_seccomp_write, __NR_seccomp_exit, __NR_seccomp_sigreturn, 518 0, /* null terminated */ 519 }; 520 521 #ifdef CONFIG_COMPAT 522 static int mode1_syscalls_32[] = { 523 __NR_seccomp_read_32, __NR_seccomp_write_32, __NR_seccomp_exit_32, __NR_seccomp_sigreturn_32, 524 0, /* null terminated */ 525 }; 526 #endif 527 528 static void __secure_computing_strict(int this_syscall) 529 { 530 int *syscall_whitelist = mode1_syscalls; 531 #ifdef CONFIG_COMPAT 532 if (in_compat_syscall()) 533 syscall_whitelist = mode1_syscalls_32; 534 #endif 535 do { 536 if (*syscall_whitelist == this_syscall) 537 return; 538 } while (*++syscall_whitelist); 539 540 #ifdef SECCOMP_DEBUG 541 dump_stack(); 542 #endif 543 audit_seccomp(this_syscall, SIGKILL, SECCOMP_RET_KILL); 544 do_exit(SIGKILL); 545 } 546 547 #ifndef CONFIG_HAVE_ARCH_SECCOMP_FILTER 548 void secure_computing_strict(int this_syscall) 549 { 550 int mode = current->seccomp.mode; 551 552 if (config_enabled(CONFIG_CHECKPOINT_RESTORE) && 553 unlikely(current->ptrace & PT_SUSPEND_SECCOMP)) 554 return; 555 556 if (mode == SECCOMP_MODE_DISABLED) 557 return; 558 else if (mode == SECCOMP_MODE_STRICT) 559 __secure_computing_strict(this_syscall); 560 else 561 BUG(); 562 } 563 #else 564 int __secure_computing(void) 565 { 566 u32 phase1_result = seccomp_phase1(NULL); 567 568 if (likely(phase1_result == SECCOMP_PHASE1_OK)) 569 return 0; 570 else if (likely(phase1_result == SECCOMP_PHASE1_SKIP)) 571 return -1; 572 else 573 return seccomp_phase2(phase1_result); 574 } 575 576 #ifdef CONFIG_SECCOMP_FILTER 577 static u32 __seccomp_phase1_filter(int this_syscall, struct seccomp_data *sd) 578 { 579 u32 filter_ret, action; 580 int data; 581 582 /* 583 * Make sure that any changes to mode from another thread have 584 * been seen after TIF_SECCOMP was seen. 585 */ 586 rmb(); 587 588 filter_ret = seccomp_run_filters(sd); 589 data = filter_ret & SECCOMP_RET_DATA; 590 action = filter_ret & SECCOMP_RET_ACTION; 591 592 switch (action) { 593 case SECCOMP_RET_ERRNO: 594 /* Set low-order bits as an errno, capped at MAX_ERRNO. */ 595 if (data > MAX_ERRNO) 596 data = MAX_ERRNO; 597 syscall_set_return_value(current, task_pt_regs(current), 598 -data, 0); 599 goto skip; 600 601 case SECCOMP_RET_TRAP: 602 /* Show the handler the original registers. */ 603 syscall_rollback(current, task_pt_regs(current)); 604 /* Let the filter pass back 16 bits of data. */ 605 seccomp_send_sigsys(this_syscall, data); 606 goto skip; 607 608 case SECCOMP_RET_TRACE: 609 return filter_ret; /* Save the rest for phase 2. */ 610 611 case SECCOMP_RET_ALLOW: 612 return SECCOMP_PHASE1_OK; 613 614 case SECCOMP_RET_KILL: 615 default: 616 audit_seccomp(this_syscall, SIGSYS, action); 617 do_exit(SIGSYS); 618 } 619 620 unreachable(); 621 622 skip: 623 audit_seccomp(this_syscall, 0, action); 624 return SECCOMP_PHASE1_SKIP; 625 } 626 #endif 627 628 /** 629 * seccomp_phase1() - run fast path seccomp checks on the current syscall 630 * @arg sd: The seccomp_data or NULL 631 * 632 * This only reads pt_regs via the syscall_xyz helpers. The only change 633 * it will make to pt_regs is via syscall_set_return_value, and it will 634 * only do that if it returns SECCOMP_PHASE1_SKIP. 635 * 636 * If sd is provided, it will not read pt_regs at all. 637 * 638 * It may also call do_exit or force a signal; these actions must be 639 * safe. 640 * 641 * If it returns SECCOMP_PHASE1_OK, the syscall passes checks and should 642 * be processed normally. 643 * 644 * If it returns SECCOMP_PHASE1_SKIP, then the syscall should not be 645 * invoked. In this case, seccomp_phase1 will have set the return value 646 * using syscall_set_return_value. 647 * 648 * If it returns anything else, then the return value should be passed 649 * to seccomp_phase2 from a context in which ptrace hooks are safe. 650 */ 651 u32 seccomp_phase1(struct seccomp_data *sd) 652 { 653 int mode = current->seccomp.mode; 654 int this_syscall = sd ? sd->nr : 655 syscall_get_nr(current, task_pt_regs(current)); 656 657 if (config_enabled(CONFIG_CHECKPOINT_RESTORE) && 658 unlikely(current->ptrace & PT_SUSPEND_SECCOMP)) 659 return SECCOMP_PHASE1_OK; 660 661 switch (mode) { 662 case SECCOMP_MODE_STRICT: 663 __secure_computing_strict(this_syscall); /* may call do_exit */ 664 return SECCOMP_PHASE1_OK; 665 #ifdef CONFIG_SECCOMP_FILTER 666 case SECCOMP_MODE_FILTER: 667 return __seccomp_phase1_filter(this_syscall, sd); 668 #endif 669 default: 670 BUG(); 671 } 672 } 673 674 /** 675 * seccomp_phase2() - finish slow path seccomp work for the current syscall 676 * @phase1_result: The return value from seccomp_phase1() 677 * 678 * This must be called from a context in which ptrace hooks can be used. 679 * 680 * Returns 0 if the syscall should be processed or -1 to skip the syscall. 681 */ 682 int seccomp_phase2(u32 phase1_result) 683 { 684 struct pt_regs *regs = task_pt_regs(current); 685 u32 action = phase1_result & SECCOMP_RET_ACTION; 686 int data = phase1_result & SECCOMP_RET_DATA; 687 688 BUG_ON(action != SECCOMP_RET_TRACE); 689 690 audit_seccomp(syscall_get_nr(current, regs), 0, action); 691 692 /* Skip these calls if there is no tracer. */ 693 if (!ptrace_event_enabled(current, PTRACE_EVENT_SECCOMP)) { 694 syscall_set_return_value(current, regs, 695 -ENOSYS, 0); 696 return -1; 697 } 698 699 /* Allow the BPF to provide the event message */ 700 ptrace_event(PTRACE_EVENT_SECCOMP, data); 701 /* 702 * The delivery of a fatal signal during event 703 * notification may silently skip tracer notification. 704 * Terminating the task now avoids executing a system 705 * call that may not be intended. 706 */ 707 if (fatal_signal_pending(current)) 708 do_exit(SIGSYS); 709 if (syscall_get_nr(current, regs) < 0) 710 return -1; /* Explicit request to skip. */ 711 712 return 0; 713 } 714 #endif /* CONFIG_HAVE_ARCH_SECCOMP_FILTER */ 715 716 long prctl_get_seccomp(void) 717 { 718 return current->seccomp.mode; 719 } 720 721 /** 722 * seccomp_set_mode_strict: internal function for setting strict seccomp 723 * 724 * Once current->seccomp.mode is non-zero, it may not be changed. 725 * 726 * Returns 0 on success or -EINVAL on failure. 727 */ 728 static long seccomp_set_mode_strict(void) 729 { 730 const unsigned long seccomp_mode = SECCOMP_MODE_STRICT; 731 long ret = -EINVAL; 732 733 spin_lock_irq(¤t->sighand->siglock); 734 735 if (!seccomp_may_assign_mode(seccomp_mode)) 736 goto out; 737 738 #ifdef TIF_NOTSC 739 disable_TSC(); 740 #endif 741 seccomp_assign_mode(current, seccomp_mode); 742 ret = 0; 743 744 out: 745 spin_unlock_irq(¤t->sighand->siglock); 746 747 return ret; 748 } 749 750 #ifdef CONFIG_SECCOMP_FILTER 751 /** 752 * seccomp_set_mode_filter: internal function for setting seccomp filter 753 * @flags: flags to change filter behavior 754 * @filter: struct sock_fprog containing filter 755 * 756 * This function may be called repeatedly to install additional filters. 757 * Every filter successfully installed will be evaluated (in reverse order) 758 * for each system call the task makes. 759 * 760 * Once current->seccomp.mode is non-zero, it may not be changed. 761 * 762 * Returns 0 on success or -EINVAL on failure. 763 */ 764 static long seccomp_set_mode_filter(unsigned int flags, 765 const char __user *filter) 766 { 767 const unsigned long seccomp_mode = SECCOMP_MODE_FILTER; 768 struct seccomp_filter *prepared = NULL; 769 long ret = -EINVAL; 770 771 /* Validate flags. */ 772 if (flags & ~SECCOMP_FILTER_FLAG_MASK) 773 return -EINVAL; 774 775 /* Prepare the new filter before holding any locks. */ 776 prepared = seccomp_prepare_user_filter(filter); 777 if (IS_ERR(prepared)) 778 return PTR_ERR(prepared); 779 780 /* 781 * Make sure we cannot change seccomp or nnp state via TSYNC 782 * while another thread is in the middle of calling exec. 783 */ 784 if (flags & SECCOMP_FILTER_FLAG_TSYNC && 785 mutex_lock_killable(¤t->signal->cred_guard_mutex)) 786 goto out_free; 787 788 spin_lock_irq(¤t->sighand->siglock); 789 790 if (!seccomp_may_assign_mode(seccomp_mode)) 791 goto out; 792 793 ret = seccomp_attach_filter(flags, prepared); 794 if (ret) 795 goto out; 796 /* Do not free the successfully attached filter. */ 797 prepared = NULL; 798 799 seccomp_assign_mode(current, seccomp_mode); 800 out: 801 spin_unlock_irq(¤t->sighand->siglock); 802 if (flags & SECCOMP_FILTER_FLAG_TSYNC) 803 mutex_unlock(¤t->signal->cred_guard_mutex); 804 out_free: 805 seccomp_filter_free(prepared); 806 return ret; 807 } 808 #else 809 static inline long seccomp_set_mode_filter(unsigned int flags, 810 const char __user *filter) 811 { 812 return -EINVAL; 813 } 814 #endif 815 816 /* Common entry point for both prctl and syscall. */ 817 static long do_seccomp(unsigned int op, unsigned int flags, 818 const char __user *uargs) 819 { 820 switch (op) { 821 case SECCOMP_SET_MODE_STRICT: 822 if (flags != 0 || uargs != NULL) 823 return -EINVAL; 824 return seccomp_set_mode_strict(); 825 case SECCOMP_SET_MODE_FILTER: 826 return seccomp_set_mode_filter(flags, uargs); 827 default: 828 return -EINVAL; 829 } 830 } 831 832 SYSCALL_DEFINE3(seccomp, unsigned int, op, unsigned int, flags, 833 const char __user *, uargs) 834 { 835 return do_seccomp(op, flags, uargs); 836 } 837 838 /** 839 * prctl_set_seccomp: configures current->seccomp.mode 840 * @seccomp_mode: requested mode to use 841 * @filter: optional struct sock_fprog for use with SECCOMP_MODE_FILTER 842 * 843 * Returns 0 on success or -EINVAL on failure. 844 */ 845 long prctl_set_seccomp(unsigned long seccomp_mode, char __user *filter) 846 { 847 unsigned int op; 848 char __user *uargs; 849 850 switch (seccomp_mode) { 851 case SECCOMP_MODE_STRICT: 852 op = SECCOMP_SET_MODE_STRICT; 853 /* 854 * Setting strict mode through prctl always ignored filter, 855 * so make sure it is always NULL here to pass the internal 856 * check in do_seccomp(). 857 */ 858 uargs = NULL; 859 break; 860 case SECCOMP_MODE_FILTER: 861 op = SECCOMP_SET_MODE_FILTER; 862 uargs = filter; 863 break; 864 default: 865 return -EINVAL; 866 } 867 868 /* prctl interface doesn't have flags, so they are always zero. */ 869 return do_seccomp(op, 0, uargs); 870 } 871 872 #if defined(CONFIG_SECCOMP_FILTER) && defined(CONFIG_CHECKPOINT_RESTORE) 873 long seccomp_get_filter(struct task_struct *task, unsigned long filter_off, 874 void __user *data) 875 { 876 struct seccomp_filter *filter; 877 struct sock_fprog_kern *fprog; 878 long ret; 879 unsigned long count = 0; 880 881 if (!capable(CAP_SYS_ADMIN) || 882 current->seccomp.mode != SECCOMP_MODE_DISABLED) { 883 return -EACCES; 884 } 885 886 spin_lock_irq(&task->sighand->siglock); 887 if (task->seccomp.mode != SECCOMP_MODE_FILTER) { 888 ret = -EINVAL; 889 goto out; 890 } 891 892 filter = task->seccomp.filter; 893 while (filter) { 894 filter = filter->prev; 895 count++; 896 } 897 898 if (filter_off >= count) { 899 ret = -ENOENT; 900 goto out; 901 } 902 count -= filter_off; 903 904 filter = task->seccomp.filter; 905 while (filter && count > 1) { 906 filter = filter->prev; 907 count--; 908 } 909 910 if (WARN_ON(count != 1 || !filter)) { 911 /* The filter tree shouldn't shrink while we're using it. */ 912 ret = -ENOENT; 913 goto out; 914 } 915 916 fprog = filter->prog->orig_prog; 917 if (!fprog) { 918 /* This must be a new non-cBPF filter, since we save every 919 * every cBPF filter's orig_prog above when 920 * CONFIG_CHECKPOINT_RESTORE is enabled. 921 */ 922 ret = -EMEDIUMTYPE; 923 goto out; 924 } 925 926 ret = fprog->len; 927 if (!data) 928 goto out; 929 930 get_seccomp_filter(task); 931 spin_unlock_irq(&task->sighand->siglock); 932 933 if (copy_to_user(data, fprog->filter, bpf_classic_proglen(fprog))) 934 ret = -EFAULT; 935 936 put_seccomp_filter(task); 937 return ret; 938 939 out: 940 spin_unlock_irq(&task->sighand->siglock); 941 return ret; 942 } 943 #endif 944