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Linux/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
908 

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