kernel/seccomp.c

   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  * @prog: the BPF program to evaluate
  45  *
  46  * seccomp_filter objects are organized in a tree linked via the @prev
  47  * pointer.  For any task, it appears to be a singly-linked list starting
  48  * with current->seccomp.filter, the most recently attached or inherited filter.
  49  * However, multiple filters may share a @prev node, by way of fork(), which
  50  * results in a unidirectional tree existing in memory.  This is similar to
  51  * how namespaces work.
  52  *
  53  * seccomp_filter objects should never be modified after being attached
  54  * to a task_struct (other than @usage).
  55  */
  56 struct seccomp_filter {
  57         atomic_t usage;
  58         struct seccomp_filter *prev;
  59         struct bpf_prog *prog;
  60 };
  61
  62 /* Limit any path through the tree to 256KB worth of instructions. */
  63 #define MAX_INSNS_PER_PATH ((1 << 18) / sizeof(struct sock_filter))
  64
  65 /*
  66  * Endianness is explicitly ignored and left for BPF program authors to manage
  67  * as per the specific architecture.
  68  */
  69 static void populate_seccomp_data(struct seccomp_data *sd)
  70 {
  71         struct task_struct *task = current;
  72         struct pt_regs *regs = task_pt_regs(task);
  73         unsigned long args[6];
  74
  75         sd->nr = syscall_get_nr(task, regs);
  76         sd->arch = syscall_get_arch();
  77         syscall_get_arguments(task, regs, 0, 6, args);
  78         sd->args[0] = args[0];
  79         sd->args[1] = args[1];
  80         sd->args[2] = args[2];
  81         sd->args[3] = args[3];
  82         sd->args[4] = args[4];
  83         sd->args[5] = args[5];
  84         sd->instruction_pointer = KSTK_EIP(task);
  85 }
  86
  87 /**
  88  *      seccomp_check_filter - verify seccomp filter code
  89  *      @filter: filter to verify
  90  *      @flen: length of filter
  91  *
  92  * Takes a previously checked filter (by bpf_check_classic) and
  93  * redirects all filter code that loads struct sk_buff data
  94  * and related data through seccomp_bpf_load.  It also
  95  * enforces length and alignment checking of those loads.
  96  *
  97  * Returns 0 if the rule set is legal or -EINVAL if not.
  98  */
  99 static int seccomp_check_filter(struct sock_filter *filter, unsigned int flen)
 100 {
 101         int pc;
 102         for (pc = 0; pc < flen; pc++) {
 103                 struct sock_filter *ftest = &filter[pc];
 104                 u16 code = ftest->code;
 105                 u32 k = ftest->k;
 106
 107                 switch (code) {
 108                 case BPF_LD | BPF_W | BPF_ABS:
 109                         ftest->code = BPF_LDX | BPF_W | BPF_ABS;
 110                         /* 32-bit aligned and not out of bounds. */
 111                         if (k >= sizeof(struct seccomp_data) || k & 3)
 112                                 return -EINVAL;
 113                         continue;
 114                 case BPF_LD | BPF_W | BPF_LEN:
 115                         ftest->code = BPF_LD | BPF_IMM;
 116                         ftest->k = sizeof(struct seccomp_data);
 117                         continue;
 118                 case BPF_LDX | BPF_W | BPF_LEN:
 119                         ftest->code = BPF_LDX | BPF_IMM;
 120                         ftest->k = sizeof(struct seccomp_data);
 121                         continue;
 122                 /* Explicitly include allowed calls. */
 123                 case BPF_RET | BPF_K:
 124                 case BPF_RET | BPF_A:
 125                 case BPF_ALU | BPF_ADD | BPF_K:
 126                 case BPF_ALU | BPF_ADD | BPF_X:
 127                 case BPF_ALU | BPF_SUB | BPF_K:
 128                 case BPF_ALU | BPF_SUB | BPF_X:
 129                 case BPF_ALU | BPF_MUL | BPF_K:
 130                 case BPF_ALU | BPF_MUL | BPF_X:
 131                 case BPF_ALU | BPF_DIV | BPF_K:
 132                 case BPF_ALU | BPF_DIV | BPF_X:
 133                 case BPF_ALU | BPF_AND | BPF_K:
 134                 case BPF_ALU | BPF_AND | BPF_X:
 135                 case BPF_ALU | BPF_OR | BPF_K:
 136                 case BPF_ALU | BPF_OR | BPF_X:
 137                 case BPF_ALU | BPF_XOR | BPF_K:
 138                 case BPF_ALU | BPF_XOR | BPF_X:
 139                 case BPF_ALU | BPF_LSH | BPF_K:
 140                 case BPF_ALU | BPF_LSH | BPF_X:
 141                 case BPF_ALU | BPF_RSH | BPF_K:
 142                 case BPF_ALU | BPF_RSH | BPF_X:
 143                 case BPF_ALU | BPF_NEG:
 144                 case BPF_LD | BPF_IMM:
 145                 case BPF_LDX | BPF_IMM:
 146                 case BPF_MISC | BPF_TAX:
 147                 case BPF_MISC | BPF_TXA:
 148                 case BPF_LD | BPF_MEM:
 149                 case BPF_LDX | BPF_MEM:
 150                 case BPF_ST:
 151                 case BPF_STX:
 152                 case BPF_JMP | BPF_JA:
 153                 case BPF_JMP | BPF_JEQ | BPF_K:
 154                 case BPF_JMP | BPF_JEQ | BPF_X:
 155                 case BPF_JMP | BPF_JGE | BPF_K:
 156                 case BPF_JMP | BPF_JGE | BPF_X:
 157                 case BPF_JMP | BPF_JGT | BPF_K:
 158                 case BPF_JMP | BPF_JGT | BPF_X:
 159                 case BPF_JMP | BPF_JSET | BPF_K:
 160                 case BPF_JMP | BPF_JSET | BPF_X:
 161                         continue;
 162                 default:
 163                         return -EINVAL;
 164                 }
 165         }
 166         return 0;
 167 }
 168
 169 /**
 170  * seccomp_run_filters - evaluates all seccomp filters against @sd
 171  * @sd: optional seccomp data to be passed to filters
 172  *
 173  * Returns valid seccomp BPF response codes.
 174  */
 175 static u32 seccomp_run_filters(const struct seccomp_data *sd)
 176 {
 177         struct seccomp_data sd_local;
 178         u32 ret = SECCOMP_RET_ALLOW;
 179         /* Make sure cross-thread synced filter points somewhere sane. */
 180         struct seccomp_filter *f =
 181                         lockless_dereference(current->seccomp.filter);
 182
 183         /* Ensure unexpected behavior doesn't result in failing open. */
 184         if (unlikely(WARN_ON(f == NULL)))
 185                 return SECCOMP_RET_KILL;
 186
 187         if (!sd) {
 188                 populate_seccomp_data(&sd_local);
 189                 sd = &sd_local;
 190         }
 191
 192         /*
 193          * All filters in the list are evaluated and the lowest BPF return
 194          * value always takes priority (ignoring the DATA).
 195          */
 196         for (; f; f = f->prev) {
 197                 u32 cur_ret = BPF_PROG_RUN(f->prog, sd);
 198
 199                 if ((cur_ret & SECCOMP_RET_ACTION) < (ret & SECCOMP_RET_ACTION))
 200                         ret = cur_ret;
 201         }
 202         return ret;
 203 }
 204 #endif /* CONFIG_SECCOMP_FILTER */
 205
 206 static inline bool seccomp_may_assign_mode(unsigned long seccomp_mode)
 207 {
 208         assert_spin_locked(&current->sighand->siglock);
 209
 210         if (current->seccomp.mode && current->seccomp.mode != seccomp_mode)
 211                 return false;
 212
 213         return true;
 214 }
 215
 216 static inline void seccomp_assign_mode(struct task_struct *task,
 217                                        unsigned long seccomp_mode)
 218 {
 219         assert_spin_locked(&task->sighand->siglock);
 220
 221         task->seccomp.mode = seccomp_mode;
 222         /*
 223          * Make sure TIF_SECCOMP cannot be set before the mode (and
 224          * filter) is set.
 225          */
 226         smp_mb__before_atomic();
 227         set_tsk_thread_flag(task, TIF_SECCOMP);
 228 }
 229
 230 #ifdef CONFIG_SECCOMP_FILTER
 231 /* Returns 1 if the parent is an ancestor of the child. */
 232 static int is_ancestor(struct seccomp_filter *parent,
 233                        struct seccomp_filter *child)
 234 {
 235         /* NULL is the root ancestor. */
 236         if (parent == NULL)
 237                 return 1;
 238         for (; child; child = child->prev)
 239                 if (child == parent)
 240                         return 1;
 241         return 0;
 242 }
 243
 244 /**
 245  * seccomp_can_sync_threads: checks if all threads can be synchronized
 246  *
 247  * Expects sighand and cred_guard_mutex locks to be held.
 248  *
 249  * Returns 0 on success, -ve on error, or the pid of a thread which was
 250  * either not in the correct seccomp mode or it did not have an ancestral
 251  * seccomp filter.
 252  */
 253 static inline pid_t seccomp_can_sync_threads(void)
 254 {
 255         struct task_struct *thread, *caller;
 256
 257         BUG_ON(!mutex_is_locked(&current->signal->cred_guard_mutex));
 258         assert_spin_locked(&current->sighand->siglock);
 259
 260         /* Validate all threads being eligible for synchronization. */
 261         caller = current;
 262         for_each_thread(caller, thread) {
 263                 pid_t failed;
 264
 265                 /* Skip current, since it is initiating the sync. */
 266                 if (thread == caller)
 267                         continue;
 268
 269                 if (thread->seccomp.mode == SECCOMP_MODE_DISABLED ||
 270                     (thread->seccomp.mode == SECCOMP_MODE_FILTER &&
 271                      is_ancestor(thread->seccomp.filter,
 272                                  caller->seccomp.filter)))
 273                         continue;
 274
 275                 /* Return the first thread that cannot be synchronized. */
 276                 failed = task_pid_vnr(thread);
 277                 /* If the pid cannot be resolved, then return -ESRCH */
 278                 if (unlikely(WARN_ON(failed == 0)))
 279                         failed = -ESRCH;
 280                 return failed;
 281         }
 282
 283         return 0;
 284 }
 285
 286 /**
 287  * seccomp_sync_threads: sets all threads to use current's filter
 288  *
 289  * Expects sighand and cred_guard_mutex locks to be held, and for
 290  * seccomp_can_sync_threads() to have returned success already
 291  * without dropping the locks.
 292  *
 293  */
 294 static inline void seccomp_sync_threads(void)
 295 {
 296         struct task_struct *thread, *caller;
 297
 298         BUG_ON(!mutex_is_locked(&current->signal->cred_guard_mutex));
 299         assert_spin_locked(&current->sighand->siglock);
 300
 301         /* Synchronize all threads. */
 302         caller = current;
 303         for_each_thread(caller, thread) {
 304                 /* Skip current, since it needs no changes. */
 305                 if (thread == caller)
 306                         continue;
 307
 308                 /* Get a task reference for the new leaf node. */
 309                 get_seccomp_filter(caller);
 310                 /*
 311                  * Drop the task reference to the shared ancestor since
 312                  * current's path will hold a reference.  (This also
 313                  * allows a put before the assignment.)
 314                  */
 315                 put_seccomp_filter(thread);
 316                 smp_store_release(&thread->seccomp.filter,
 317                                   caller->seccomp.filter);
 318
 319                 /*
 320                  * Don't let an unprivileged task work around
 321                  * the no_new_privs restriction by creating
 322                  * a thread that sets it up, enters seccomp,
 323                  * then dies.
 324                  */
 325                 if (task_no_new_privs(caller))
 326                         task_set_no_new_privs(thread);
 327
 328                 /*
 329                  * Opt the other thread into seccomp if needed.
 330                  * As threads are considered to be trust-realm
 331                  * equivalent (see ptrace_may_access), it is safe to
 332                  * allow one thread to transition the other.
 333                  */
 334                 if (thread->seccomp.mode == SECCOMP_MODE_DISABLED)
 335                         seccomp_assign_mode(thread, SECCOMP_MODE_FILTER);
 336         }
 337 }
 338
 339 /**
 340  * seccomp_prepare_filter: Prepares a seccomp filter for use.
 341  * @fprog: BPF program to install
 342  *
 343  * Returns filter on success or an ERR_PTR on failure.
 344  */
 345 static struct seccomp_filter *seccomp_prepare_filter(struct sock_fprog *fprog)
 346 {
 347         struct seccomp_filter *sfilter;
 348         int ret;
 349         const bool save_orig = IS_ENABLED(CONFIG_CHECKPOINT_RESTORE);
 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, save_orig);
 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 (in_compat_syscall()) {
 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(&current->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_destroy(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 const int mode1_syscalls[] = {
 516         __NR_seccomp_read, __NR_seccomp_write, __NR_seccomp_exit, __NR_seccomp_sigreturn,
 517         0, /* null terminated */
 518 };
 519
 520 static void __secure_computing_strict(int this_syscall)
 521 {
 522         const int *syscall_whitelist = mode1_syscalls;
 523 #ifdef CONFIG_COMPAT
 524         if (in_compat_syscall())
 525                 syscall_whitelist = get_compat_mode1_syscalls();
 526 #endif
 527         do {
 528                 if (*syscall_whitelist == this_syscall)
 529                         return;
 530         } while (*++syscall_whitelist);
 531
 532 #ifdef SECCOMP_DEBUG
 533         dump_stack();
 534 #endif
 535         audit_seccomp(this_syscall, SIGKILL, SECCOMP_RET_KILL);
 536         do_exit(SIGKILL);
 537 }
 538
 539 #ifndef CONFIG_HAVE_ARCH_SECCOMP_FILTER
 540 void secure_computing_strict(int this_syscall)
 541 {
 542         int mode = current->seccomp.mode;
 543
 544         if (IS_ENABLED(CONFIG_CHECKPOINT_RESTORE) &&
 545             unlikely(current->ptrace & PT_SUSPEND_SECCOMP))
 546                 return;
 547
 548         if (mode == SECCOMP_MODE_DISABLED)
 549                 return;
 550         else if (mode == SECCOMP_MODE_STRICT)
 551                 __secure_computing_strict(this_syscall);
 552         else
 553                 BUG();
 554 }
 555 #else
 556
 557 #ifdef CONFIG_SECCOMP_FILTER
 558 static int __seccomp_filter(int this_syscall, const struct seccomp_data *sd,
 559                             const bool recheck_after_trace)
 560 {
 561         u32 filter_ret, action;
 562         int data;
 563
 564         /*
 565          * Make sure that any changes to mode from another thread have
 566          * been seen after TIF_SECCOMP was seen.
 567          */
 568         rmb();
 569
 570         filter_ret = seccomp_run_filters(sd);
 571         data = filter_ret & SECCOMP_RET_DATA;
 572         action = filter_ret & SECCOMP_RET_ACTION;
 573
 574         switch (action) {
 575         case SECCOMP_RET_ERRNO:
 576                 /* Set low-order bits as an errno, capped at MAX_ERRNO. */
 577                 if (data > MAX_ERRNO)
 578                         data = MAX_ERRNO;
 579                 syscall_set_return_value(current, task_pt_regs(current),
 580                                          -data, 0);
 581                 goto skip;
 582
 583         case SECCOMP_RET_TRAP:
 584                 /* Show the handler the original registers. */
 585                 syscall_rollback(current, task_pt_regs(current));
 586                 /* Let the filter pass back 16 bits of data. */
 587                 seccomp_send_sigsys(this_syscall, data);
 588                 goto skip;
 589
 590         case SECCOMP_RET_TRACE:
 591                 /* We've been put in this state by the ptracer already. */
 592                 if (recheck_after_trace)
 593                         return 0;
 594
 595                 /* ENOSYS these calls if there is no tracer attached. */
 596                 if (!ptrace_event_enabled(current, PTRACE_EVENT_SECCOMP)) {
 597                         syscall_set_return_value(current,
 598                                                  task_pt_regs(current),
 599                                                  -ENOSYS, 0);
 600                         goto skip;
 601                 }
 602
 603                 /* Allow the BPF to provide the event message */
 604                 ptrace_event(PTRACE_EVENT_SECCOMP, data);
 605                 /*
 606                  * The delivery of a fatal signal during event
 607                  * notification may silently skip tracer notification,
 608                  * which could leave us with a potentially unmodified
 609                  * syscall that the tracer would have liked to have
 610                  * changed. Since the process is about to die, we just
 611                  * force the syscall to be skipped and let the signal
 612                  * kill the process and correctly handle any tracer exit
 613                  * notifications.
 614                  */
 615                 if (fatal_signal_pending(current))
 616                         goto skip;
 617                 /* Check if the tracer forced the syscall to be skipped. */
 618                 this_syscall = syscall_get_nr(current, task_pt_regs(current));
 619                 if (this_syscall < 0)
 620                         goto skip;
 621
 622                 /*
 623                  * Recheck the syscall, since it may have changed. This
 624                  * intentionally uses a NULL struct seccomp_data to force
 625                  * a reload of all registers. This does not goto skip since
 626                  * a skip would have already been reported.
 627                  */
 628                 if (__seccomp_filter(this_syscall, NULL, true))
 629                         return -1;
 630
 631                 return 0;
 632
 633         case SECCOMP_RET_ALLOW:
 634                 return 0;
 635
 636         case SECCOMP_RET_KILL:
 637         default:
 638                 audit_seccomp(this_syscall, SIGSYS, action);
 639                 do_exit(SIGSYS);
 640         }
 641
 642         unreachable();
 643
 644 skip:
 645         audit_seccomp(this_syscall, 0, action);
 646         return -1;
 647 }
 648 #else
 649 static int __seccomp_filter(int this_syscall, const struct seccomp_data *sd,
 650                             const bool recheck_after_trace)
 651 {
 652         BUG();
 653 }
 654 #endif
 655
 656 int __secure_computing(const struct seccomp_data *sd)
 657 {
 658         int mode = current->seccomp.mode;
 659         int this_syscall;
 660
 661         if (IS_ENABLED(CONFIG_CHECKPOINT_RESTORE) &&
 662             unlikely(current->ptrace & PT_SUSPEND_SECCOMP))
 663                 return 0;
 664
 665         this_syscall = sd ? sd->nr :
 666                 syscall_get_nr(current, task_pt_regs(current));
 667
 668         switch (mode) {
 669         case SECCOMP_MODE_STRICT:
 670                 __secure_computing_strict(this_syscall);  /* may call do_exit */
 671                 return 0;
 672         case SECCOMP_MODE_FILTER:
 673                 return __seccomp_filter(this_syscall, sd, false);
 674         default:
 675                 BUG();
 676         }
 677 }
 678 #endif /* CONFIG_HAVE_ARCH_SECCOMP_FILTER */
 679
 680 long prctl_get_seccomp(void)
 681 {
 682         return current->seccomp.mode;
 683 }
 684
 685 /**
 686  * seccomp_set_mode_strict: internal function for setting strict seccomp
 687  *
 688  * Once current->seccomp.mode is non-zero, it may not be changed.
 689  *
 690  * Returns 0 on success or -EINVAL on failure.
 691  */
 692 static long seccomp_set_mode_strict(void)
 693 {
 694         const unsigned long seccomp_mode = SECCOMP_MODE_STRICT;
 695         long ret = -EINVAL;
 696
 697         spin_lock_irq(&current->sighand->siglock);
 698
 699         if (!seccomp_may_assign_mode(seccomp_mode))
 700                 goto out;
 701
 702 #ifdef TIF_NOTSC
 703         disable_TSC();
 704 #endif
 705         seccomp_assign_mode(current, seccomp_mode);
 706         ret = 0;
 707
 708 out:
 709         spin_unlock_irq(&current->sighand->siglock);
 710
 711         return ret;
 712 }
 713
 714 #ifdef CONFIG_SECCOMP_FILTER
 715 /**
 716  * seccomp_set_mode_filter: internal function for setting seccomp filter
 717  * @flags:  flags to change filter behavior
 718  * @filter: struct sock_fprog containing filter
 719  *
 720  * This function may be called repeatedly to install additional filters.
 721  * Every filter successfully installed will be evaluated (in reverse order)
 722  * for each system call the task makes.
 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_filter(unsigned int flags,
 729                                     const char __user *filter)
 730 {
 731         const unsigned long seccomp_mode = SECCOMP_MODE_FILTER;
 732         struct seccomp_filter *prepared = NULL;
 733         long ret = -EINVAL;
 734
 735         /* Validate flags. */
 736         if (flags & ~SECCOMP_FILTER_FLAG_MASK)
 737                 return -EINVAL;
 738
 739         /* Prepare the new filter before holding any locks. */
 740         prepared = seccomp_prepare_user_filter(filter);
 741         if (IS_ERR(prepared))
 742                 return PTR_ERR(prepared);
 743
 744         /*
 745          * Make sure we cannot change seccomp or nnp state via TSYNC
 746          * while another thread is in the middle of calling exec.
 747          */
 748         if (flags & SECCOMP_FILTER_FLAG_TSYNC &&
 749             mutex_lock_killable(&current->signal->cred_guard_mutex))
 750                 goto out_free;
 751
 752         spin_lock_irq(&current->sighand->siglock);
 753
 754         if (!seccomp_may_assign_mode(seccomp_mode))
 755                 goto out;
 756
 757         ret = seccomp_attach_filter(flags, prepared);
 758         if (ret)
 759                 goto out;
 760         /* Do not free the successfully attached filter. */
 761         prepared = NULL;
 762
 763         seccomp_assign_mode(current, seccomp_mode);
 764 out:
 765         spin_unlock_irq(&current->sighand->siglock);
 766         if (flags & SECCOMP_FILTER_FLAG_TSYNC)
 767                 mutex_unlock(&current->signal->cred_guard_mutex);
 768 out_free:
 769         seccomp_filter_free(prepared);
 770         return ret;
 771 }
 772 #else
 773 static inline long seccomp_set_mode_filter(unsigned int flags,
 774                                            const char __user *filter)
 775 {
 776         return -EINVAL;
 777 }
 778 #endif
 779
 780 /* Common entry point for both prctl and syscall. */
 781 static long do_seccomp(unsigned int op, unsigned int flags,
 782                        const char __user *uargs)
 783 {
 784         switch (op) {
 785         case SECCOMP_SET_MODE_STRICT:
 786                 if (flags != 0 || uargs != NULL)
 787                         return -EINVAL;
 788                 return seccomp_set_mode_strict();
 789         case SECCOMP_SET_MODE_FILTER:
 790                 return seccomp_set_mode_filter(flags, uargs);
 791         default:
 792                 return -EINVAL;
 793         }
 794 }
 795
 796 SYSCALL_DEFINE3(seccomp, unsigned int, op, unsigned int, flags,
 797                          const char __user *, uargs)
 798 {
 799         return do_seccomp(op, flags, uargs);
 800 }
 801
 802 /**
 803  * prctl_set_seccomp: configures current->seccomp.mode
 804  * @seccomp_mode: requested mode to use
 805  * @filter: optional struct sock_fprog for use with SECCOMP_MODE_FILTER
 806  *
 807  * Returns 0 on success or -EINVAL on failure.
 808  */
 809 long prctl_set_seccomp(unsigned long seccomp_mode, char __user *filter)
 810 {
 811         unsigned int op;
 812         char __user *uargs;
 813
 814         switch (seccomp_mode) {
 815         case SECCOMP_MODE_STRICT:
 816                 op = SECCOMP_SET_MODE_STRICT;
 817                 /*
 818                  * Setting strict mode through prctl always ignored filter,
 819                  * so make sure it is always NULL here to pass the internal
 820                  * check in do_seccomp().
 821                  */
 822                 uargs = NULL;
 823                 break;
 824         case SECCOMP_MODE_FILTER:
 825                 op = SECCOMP_SET_MODE_FILTER;
 826                 uargs = filter;
 827                 break;
 828         default:
 829                 return -EINVAL;
 830         }
 831
 832         /* prctl interface doesn't have flags, so they are always zero. */
 833         return do_seccomp(op, 0, uargs);
 834 }
 835
 836 #if defined(CONFIG_SECCOMP_FILTER) && defined(CONFIG_CHECKPOINT_RESTORE)
 837 long seccomp_get_filter(struct task_struct *task, unsigned long filter_off,
 838                         void __user *data)
 839 {
 840         struct seccomp_filter *filter;
 841         struct sock_fprog_kern *fprog;
 842         long ret;
 843         unsigned long count = 0;
 844
 845         if (!capable(CAP_SYS_ADMIN) ||
 846             current->seccomp.mode != SECCOMP_MODE_DISABLED) {
 847                 return -EACCES;
 848         }
 849
 850         spin_lock_irq(&task->sighand->siglock);
 851         if (task->seccomp.mode != SECCOMP_MODE_FILTER) {
 852                 ret = -EINVAL;
 853                 goto out;
 854         }
 855
 856         filter = task->seccomp.filter;
 857         while (filter) {
 858                 filter = filter->prev;
 859                 count++;
 860         }
 861
 862         if (filter_off >= count) {
 863                 ret = -ENOENT;
 864                 goto out;
 865         }
 866         count -= filter_off;
 867
 868         filter = task->seccomp.filter;
 869         while (filter && count > 1) {
 870                 filter = filter->prev;
 871                 count--;
 872         }
 873
 874         if (WARN_ON(count != 1 || !filter)) {
 875                 /* The filter tree shouldn't shrink while we're using it. */
 876                 ret = -ENOENT;
 877                 goto out;
 878         }
 879
 880         fprog = filter->prog->orig_prog;
 881         if (!fprog) {
 882                 /* This must be a new non-cBPF filter, since we save
 883                  * every cBPF filter's orig_prog above when
 884                  * CONFIG_CHECKPOINT_RESTORE is enabled.
 885                  */
 886                 ret = -EMEDIUMTYPE;
 887                 goto out;
 888         }
 889
 890         ret = fprog->len;
 891         if (!data)
 892                 goto out;
 893
 894         get_seccomp_filter(task);
 895         spin_unlock_irq(&task->sighand->siglock);
 896
 897         if (copy_to_user(data, fprog->filter, bpf_classic_proglen(fprog)))
 898                 ret = -EFAULT;
 899
 900         put_seccomp_filter(task);
 901         return ret;
 902
 903 out:
 904         spin_unlock_irq(&task->sighand->siglock);
 905         return ret;
 906 }
 907 #endif