linux/kernel/seccomp.c
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   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 */
  57struct 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 */
  70static 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 */
 100static 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 */
 176static u32 seccomp_run_filters(const 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
 207static inline bool seccomp_may_assign_mode(unsigned long seccomp_mode)
 208{
 209        assert_spin_locked(&current->sighand->siglock);
 210
 211        if (current->seccomp.mode && current->seccomp.mode != seccomp_mode)
 212                return false;
 213
 214        return true;
 215}
 216
 217static 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. */
 233static 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 */
 254static inline pid_t seccomp_can_sync_threads(void)
 255{
 256        struct task_struct *thread, *caller;
 257
 258        BUG_ON(!mutex_is_locked(&current->signal->cred_guard_mutex));
 259        assert_spin_locked(&current->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 */
 295static inline void seccomp_sync_threads(void)
 296{
 297        struct task_struct *thread, *caller;
 298
 299        BUG_ON(!mutex_is_locked(&current->signal->cred_guard_mutex));
 300        assert_spin_locked(&current->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 */
 346static struct seccomp_filter *seccomp_prepare_filter(struct sock_fprog *fprog)
 347{
 348        struct seccomp_filter *sfilter;
 349        int ret;
 350        const bool save_orig = IS_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 */
 391static struct seccomp_filter *
 392seccomp_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);
 409out:
 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 */
 422static 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(&current->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 */
 461void 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
 470static 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 */
 479void 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 */
 497static 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 */
 516static const int mode1_syscalls[] = {
 517        __NR_seccomp_read, __NR_seccomp_write, __NR_seccomp_exit, __NR_seccomp_sigreturn,
 518        0, /* null terminated */
 519};
 520
 521static void __secure_computing_strict(int this_syscall)
 522{
 523        const int *syscall_whitelist = mode1_syscalls;
 524#ifdef CONFIG_COMPAT
 525        if (in_compat_syscall())
 526                syscall_whitelist = get_compat_mode1_syscalls();
 527#endif
 528        do {
 529                if (*syscall_whitelist == this_syscall)
 530                        return;
 531        } while (*++syscall_whitelist);
 532
 533#ifdef SECCOMP_DEBUG
 534        dump_stack();
 535#endif
 536        audit_seccomp(this_syscall, SIGKILL, SECCOMP_RET_KILL);
 537        do_exit(SIGKILL);
 538}
 539
 540#ifndef CONFIG_HAVE_ARCH_SECCOMP_FILTER
 541void secure_computing_strict(int this_syscall)
 542{
 543        int mode = current->seccomp.mode;
 544
 545        if (IS_ENABLED(CONFIG_CHECKPOINT_RESTORE) &&
 546            unlikely(current->ptrace & PT_SUSPEND_SECCOMP))
 547                return;
 548
 549        if (mode == SECCOMP_MODE_DISABLED)
 550                return;
 551        else if (mode == SECCOMP_MODE_STRICT)
 552                __secure_computing_strict(this_syscall);
 553        else
 554                BUG();
 555}
 556#else
 557
 558#ifdef CONFIG_SECCOMP_FILTER
 559static int __seccomp_filter(int this_syscall, const struct seccomp_data *sd,
 560                            const bool recheck_after_trace)
 561{
 562        u32 filter_ret, action;
 563        int data;
 564
 565        /*
 566         * Make sure that any changes to mode from another thread have
 567         * been seen after TIF_SECCOMP was seen.
 568         */
 569        rmb();
 570
 571        filter_ret = seccomp_run_filters(sd);
 572        data = filter_ret & SECCOMP_RET_DATA;
 573        action = filter_ret & SECCOMP_RET_ACTION;
 574
 575        switch (action) {
 576        case SECCOMP_RET_ERRNO:
 577                /* Set low-order bits as an errno, capped at MAX_ERRNO. */
 578                if (data > MAX_ERRNO)
 579                        data = MAX_ERRNO;
 580                syscall_set_return_value(current, task_pt_regs(current),
 581                                         -data, 0);
 582                goto skip;
 583
 584        case SECCOMP_RET_TRAP:
 585                /* Show the handler the original registers. */
 586                syscall_rollback(current, task_pt_regs(current));
 587                /* Let the filter pass back 16 bits of data. */
 588                seccomp_send_sigsys(this_syscall, data);
 589                goto skip;
 590
 591        case SECCOMP_RET_TRACE:
 592                /* We've been put in this state by the ptracer already. */
 593                if (recheck_after_trace)
 594                        return 0;
 595
 596                /* ENOSYS these calls if there is no tracer attached. */
 597                if (!ptrace_event_enabled(current, PTRACE_EVENT_SECCOMP)) {
 598                        syscall_set_return_value(current,
 599                                                 task_pt_regs(current),
 600                                                 -ENOSYS, 0);
 601                        goto skip;
 602                }
 603
 604                /* Allow the BPF to provide the event message */
 605                ptrace_event(PTRACE_EVENT_SECCOMP, data);
 606                /*
 607                 * The delivery of a fatal signal during event
 608                 * notification may silently skip tracer notification,
 609                 * which could leave us with a potentially unmodified
 610                 * syscall that the tracer would have liked to have
 611                 * changed. Since the process is about to die, we just
 612                 * force the syscall to be skipped and let the signal
 613                 * kill the process and correctly handle any tracer exit
 614                 * notifications.
 615                 */
 616                if (fatal_signal_pending(current))
 617                        goto skip;
 618                /* Check if the tracer forced the syscall to be skipped. */
 619                this_syscall = syscall_get_nr(current, task_pt_regs(current));
 620                if (this_syscall < 0)
 621                        goto skip;
 622
 623                /*
 624                 * Recheck the syscall, since it may have changed. This
 625                 * intentionally uses a NULL struct seccomp_data to force
 626                 * a reload of all registers. This does not goto skip since
 627                 * a skip would have already been reported.
 628                 */
 629                if (__seccomp_filter(this_syscall, NULL, true))
 630                        return -1;
 631
 632                return 0;
 633
 634        case SECCOMP_RET_ALLOW:
 635                return 0;
 636
 637        case SECCOMP_RET_KILL:
 638        default:
 639                audit_seccomp(this_syscall, SIGSYS, action);
 640                do_exit(SIGSYS);
 641        }
 642
 643        unreachable();
 644
 645skip:
 646        audit_seccomp(this_syscall, 0, action);
 647        return -1;
 648}
 649#else
 650static int __seccomp_filter(int this_syscall, const struct seccomp_data *sd,
 651                            const bool recheck_after_trace)
 652{
 653        BUG();
 654}
 655#endif
 656
 657int __secure_computing(const struct seccomp_data *sd)
 658{
 659        int mode = current->seccomp.mode;
 660        int this_syscall;
 661
 662        if (IS_ENABLED(CONFIG_CHECKPOINT_RESTORE) &&
 663            unlikely(current->ptrace & PT_SUSPEND_SECCOMP))
 664                return 0;
 665
 666        this_syscall = sd ? sd->nr :
 667                syscall_get_nr(current, task_pt_regs(current));
 668
 669        switch (mode) {
 670        case SECCOMP_MODE_STRICT:
 671                __secure_computing_strict(this_syscall);  /* may call do_exit */
 672                return 0;
 673        case SECCOMP_MODE_FILTER:
 674                return __seccomp_filter(this_syscall, sd, false);
 675        default:
 676                BUG();
 677        }
 678}
 679#endif /* CONFIG_HAVE_ARCH_SECCOMP_FILTER */
 680
 681long prctl_get_seccomp(void)
 682{
 683        return current->seccomp.mode;
 684}
 685
 686/**
 687 * seccomp_set_mode_strict: internal function for setting strict seccomp
 688 *
 689 * Once current->seccomp.mode is non-zero, it may not be changed.
 690 *
 691 * Returns 0 on success or -EINVAL on failure.
 692 */
 693static long seccomp_set_mode_strict(void)
 694{
 695        const unsigned long seccomp_mode = SECCOMP_MODE_STRICT;
 696        long ret = -EINVAL;
 697
 698        spin_lock_irq(&current->sighand->siglock);
 699
 700        if (!seccomp_may_assign_mode(seccomp_mode))
 701                goto out;
 702
 703#ifdef TIF_NOTSC
 704        disable_TSC();
 705#endif
 706        seccomp_assign_mode(current, seccomp_mode);
 707        ret = 0;
 708
 709out:
 710        spin_unlock_irq(&current->sighand->siglock);
 711
 712        return ret;
 713}
 714
 715#ifdef CONFIG_SECCOMP_FILTER
 716/**
 717 * seccomp_set_mode_filter: internal function for setting seccomp filter
 718 * @flags:  flags to change filter behavior
 719 * @filter: struct sock_fprog containing filter
 720 *
 721 * This function may be called repeatedly to install additional filters.
 722 * Every filter successfully installed will be evaluated (in reverse order)
 723 * for each system call the task makes.
 724 *
 725 * Once current->seccomp.mode is non-zero, it may not be changed.
 726 *
 727 * Returns 0 on success or -EINVAL on failure.
 728 */
 729static long seccomp_set_mode_filter(unsigned int flags,
 730                                    const char __user *filter)
 731{
 732        const unsigned long seccomp_mode = SECCOMP_MODE_FILTER;
 733        struct seccomp_filter *prepared = NULL;
 734        long ret = -EINVAL;
 735
 736        /* Validate flags. */
 737        if (flags & ~SECCOMP_FILTER_FLAG_MASK)
 738                return -EINVAL;
 739
 740        /* Prepare the new filter before holding any locks. */
 741        prepared = seccomp_prepare_user_filter(filter);
 742        if (IS_ERR(prepared))
 743                return PTR_ERR(prepared);
 744
 745        /*
 746         * Make sure we cannot change seccomp or nnp state via TSYNC
 747         * while another thread is in the middle of calling exec.
 748         */
 749        if (flags & SECCOMP_FILTER_FLAG_TSYNC &&
 750            mutex_lock_killable(&current->signal->cred_guard_mutex))
 751                goto out_free;
 752
 753        spin_lock_irq(&current->sighand->siglock);
 754
 755        if (!seccomp_may_assign_mode(seccomp_mode))
 756                goto out;
 757
 758        ret = seccomp_attach_filter(flags, prepared);
 759        if (ret)
 760                goto out;
 761        /* Do not free the successfully attached filter. */
 762        prepared = NULL;
 763
 764        seccomp_assign_mode(current, seccomp_mode);
 765out:
 766        spin_unlock_irq(&current->sighand->siglock);
 767        if (flags & SECCOMP_FILTER_FLAG_TSYNC)
 768                mutex_unlock(&current->signal->cred_guard_mutex);
 769out_free:
 770        seccomp_filter_free(prepared);
 771        return ret;
 772}
 773#else
 774static inline long seccomp_set_mode_filter(unsigned int flags,
 775                                           const char __user *filter)
 776{
 777        return -EINVAL;
 778}
 779#endif
 780
 781/* Common entry point for both prctl and syscall. */
 782static long do_seccomp(unsigned int op, unsigned int flags,
 783                       const char __user *uargs)
 784{
 785        switch (op) {
 786        case SECCOMP_SET_MODE_STRICT:
 787                if (flags != 0 || uargs != NULL)
 788                        return -EINVAL;
 789                return seccomp_set_mode_strict();
 790        case SECCOMP_SET_MODE_FILTER:
 791                return seccomp_set_mode_filter(flags, uargs);
 792        default:
 793                return -EINVAL;
 794        }
 795}
 796
 797SYSCALL_DEFINE3(seccomp, unsigned int, op, unsigned int, flags,
 798                         const char __user *, uargs)
 799{
 800        return do_seccomp(op, flags, uargs);
 801}
 802
 803/**
 804 * prctl_set_seccomp: configures current->seccomp.mode
 805 * @seccomp_mode: requested mode to use
 806 * @filter: optional struct sock_fprog for use with SECCOMP_MODE_FILTER
 807 *
 808 * Returns 0 on success or -EINVAL on failure.
 809 */
 810long prctl_set_seccomp(unsigned long seccomp_mode, char __user *filter)
 811{
 812        unsigned int op;
 813        char __user *uargs;
 814
 815        switch (seccomp_mode) {
 816        case SECCOMP_MODE_STRICT:
 817                op = SECCOMP_SET_MODE_STRICT;
 818                /*
 819                 * Setting strict mode through prctl always ignored filter,
 820                 * so make sure it is always NULL here to pass the internal
 821                 * check in do_seccomp().
 822                 */
 823                uargs = NULL;
 824                break;
 825        case SECCOMP_MODE_FILTER:
 826                op = SECCOMP_SET_MODE_FILTER;
 827                uargs = filter;
 828                break;
 829        default:
 830                return -EINVAL;
 831        }
 832
 833        /* prctl interface doesn't have flags, so they are always zero. */
 834        return do_seccomp(op, 0, uargs);
 835}
 836
 837#if defined(CONFIG_SECCOMP_FILTER) && defined(CONFIG_CHECKPOINT_RESTORE)
 838long seccomp_get_filter(struct task_struct *task, unsigned long filter_off,
 839                        void __user *data)
 840{
 841        struct seccomp_filter *filter;
 842        struct sock_fprog_kern *fprog;
 843        long ret;
 844        unsigned long count = 0;
 845
 846        if (!capable(CAP_SYS_ADMIN) ||
 847            current->seccomp.mode != SECCOMP_MODE_DISABLED) {
 848                return -EACCES;
 849        }
 850
 851        spin_lock_irq(&task->sighand->siglock);
 852        if (task->seccomp.mode != SECCOMP_MODE_FILTER) {
 853                ret = -EINVAL;
 854                goto out;
 855        }
 856
 857        filter = task->seccomp.filter;
 858        while (filter) {
 859                filter = filter->prev;
 860                count++;
 861        }
 862
 863        if (filter_off >= count) {
 864                ret = -ENOENT;
 865                goto out;
 866        }
 867        count -= filter_off;
 868
 869        filter = task->seccomp.filter;
 870        while (filter && count > 1) {
 871                filter = filter->prev;
 872                count--;
 873        }
 874
 875        if (WARN_ON(count != 1 || !filter)) {
 876                /* The filter tree shouldn't shrink while we're using it. */
 877                ret = -ENOENT;
 878                goto out;
 879        }
 880
 881        fprog = filter->prog->orig_prog;
 882        if (!fprog) {
 883                /* This must be a new non-cBPF filter, since we save
 884                 * every cBPF filter's orig_prog above when
 885                 * CONFIG_CHECKPOINT_RESTORE is enabled.
 886                 */
 887                ret = -EMEDIUMTYPE;
 888                goto out;
 889        }
 890
 891        ret = fprog->len;
 892        if (!data)
 893                goto out;
 894
 895        get_seccomp_filter(task);
 896        spin_unlock_irq(&task->sighand->siglock);
 897
 898        if (copy_to_user(data, fprog->filter, bpf_classic_proglen(fprog)))
 899                ret = -EFAULT;
 900
 901        put_seccomp_filter(task);
 902        return ret;
 903
 904out:
 905        spin_unlock_irq(&task->sighand->siglock);
 906        return ret;
 907}
 908#endif
 909