projects/linux·blob v3.16-rc3 · refs

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1/*
2 * linux/kernel/seccomp.c
3 *
4 * Copyright 2004-2005 Andrea Arcangeli <[email protected]>
5 *
6 * Copyright (C) 2012 Google, Inc.
7 * Will Drewry <[email protected]>
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
22/* #define SECCOMP_DEBUG 1 */
23
24#ifdef CONFIG_SECCOMP_FILTER
25#include <asm/syscall.h>
26#include <linux/filter.h>
27#include <linux/ptrace.h>
28#include <linux/security.h>
29#include <linux/slab.h>
30#include <linux/tracehook.h>
31#include <linux/uaccess.h>
32
33/**
34 * struct seccomp_filter - container for seccomp BPF programs
35 *
36 * @usage: reference count to manage the object lifetime.
37 * get/put helpers should be used when accessing an instance
38 * outside of a lifetime-guarded section. In general, this
39 * is only needed for handling filters shared across tasks.
40 * @prev: points to a previously installed, or inherited, filter
41 * @len: the number of instructions in the program
42 * @insnsi: the BPF program instructions to evaluate
43 *
44 * seccomp_filter objects are organized in a tree linked via the @prev
45 * pointer. For any task, it appears to be a singly-linked list starting
46 * with current->seccomp.filter, the most recently attached or inherited filter.
47 * However, multiple filters may share a @prev node, by way of fork(), which
48 * results in a unidirectional tree existing in memory. This is similar to
49 * how namespaces work.
50 *
51 * seccomp_filter objects should never be modified after being attached
52 * to a task_struct (other than @usage).
53 */
54struct seccomp_filter {
55 atomic_t usage;
56 struct seccomp_filter *prev;
57 struct sk_filter *prog;
58};
59
60/* Limit any path through the tree to 256KB worth of instructions. */
61#define MAX_INSNS_PER_PATH ((1 << 18) / sizeof(struct sock_filter))
62
63/*
64 * Endianness is explicitly ignored and left for BPF program authors to manage
65 * as per the specific architecture.
66 */
67static void populate_seccomp_data(struct seccomp_data *sd)
68{
69 struct task_struct *task = current;
70 struct pt_regs *regs = task_pt_regs(task);
71 unsigned long args[6];
72
73 sd->nr = syscall_get_nr(task, regs);
74 sd->arch = syscall_get_arch();
75 syscall_get_arguments(task, regs, 0, 6, args);
76 sd->args[0] = args[0];
77 sd->args[1] = args[1];
78 sd->args[2] = args[2];
79 sd->args[3] = args[3];
80 sd->args[4] = args[4];
81 sd->args[5] = args[5];
82 sd->instruction_pointer = KSTK_EIP(task);
83}
84
85/**
86 * seccomp_check_filter - verify seccomp filter code
87 * @filter: filter to verify
88 * @flen: length of filter
89 *
90 * Takes a previously checked filter (by sk_chk_filter) and
91 * redirects all filter code that loads struct sk_buff data
92 * and related data through seccomp_bpf_load. It also
93 * enforces length and alignment checking of those loads.
94 *
95 * Returns 0 if the rule set is legal or -EINVAL if not.
96 */
97static int seccomp_check_filter(struct sock_filter *filter, unsigned int flen)
98{
99 int pc;
100 for (pc = 0; pc < flen; pc++) {
101 struct sock_filter *ftest = &filter[pc];
102 u16 code = ftest->code;
103 u32 k = ftest->k;
104
105 switch (code) {
106 case BPF_LD | BPF_W | BPF_ABS:
107 ftest->code = BPF_LDX | BPF_W | BPF_ABS;
108 /* 32-bit aligned and not out of bounds. */
109 if (k >= sizeof(struct seccomp_data) || k & 3)
110 return -EINVAL;
111 continue;
112 case BPF_LD | BPF_W | BPF_LEN:
113 ftest->code = BPF_LD | BPF_IMM;
114 ftest->k = sizeof(struct seccomp_data);
115 continue;
116 case BPF_LDX | BPF_W | BPF_LEN:
117 ftest->code = BPF_LDX | BPF_IMM;
118 ftest->k = sizeof(struct seccomp_data);
119 continue;
120 /* Explicitly include allowed calls. */
121 case BPF_RET | BPF_K:
122 case BPF_RET | BPF_A:
123 case BPF_ALU | BPF_ADD | BPF_K:
124 case BPF_ALU | BPF_ADD | BPF_X:
125 case BPF_ALU | BPF_SUB | BPF_K:
126 case BPF_ALU | BPF_SUB | BPF_X:
127 case BPF_ALU | BPF_MUL | BPF_K:
128 case BPF_ALU | BPF_MUL | BPF_X:
129 case BPF_ALU | BPF_DIV | BPF_K:
130 case BPF_ALU | BPF_DIV | BPF_X:
131 case BPF_ALU | BPF_AND | BPF_K:
132 case BPF_ALU | BPF_AND | BPF_X:
133 case BPF_ALU | BPF_OR | BPF_K:
134 case BPF_ALU | BPF_OR | BPF_X:
135 case BPF_ALU | BPF_XOR | BPF_K:
136 case BPF_ALU | BPF_XOR | BPF_X:
137 case BPF_ALU | BPF_LSH | BPF_K:
138 case BPF_ALU | BPF_LSH | BPF_X:
139 case BPF_ALU | BPF_RSH | BPF_K:
140 case BPF_ALU | BPF_RSH | BPF_X:
141 case BPF_ALU | BPF_NEG:
142 case BPF_LD | BPF_IMM:
143 case BPF_LDX | BPF_IMM:
144 case BPF_MISC | BPF_TAX:
145 case BPF_MISC | BPF_TXA:
146 case BPF_LD | BPF_MEM:
147 case BPF_LDX | BPF_MEM:
148 case BPF_ST:
149 case BPF_STX:
150 case BPF_JMP | BPF_JA:
151 case BPF_JMP | BPF_JEQ | BPF_K:
152 case BPF_JMP | BPF_JEQ | BPF_X:
153 case BPF_JMP | BPF_JGE | BPF_K:
154 case BPF_JMP | BPF_JGE | BPF_X:
155 case BPF_JMP | BPF_JGT | BPF_K:
156 case BPF_JMP | BPF_JGT | BPF_X:
157 case BPF_JMP | BPF_JSET | BPF_K:
158 case BPF_JMP | BPF_JSET | BPF_X:
159 continue;
160 default:
161 return -EINVAL;
162 }
163 }
164 return 0;
165}
166
167/**
168 * seccomp_run_filters - evaluates all seccomp filters against @syscall
169 * @syscall: number of the current system call
170 *
171 * Returns valid seccomp BPF response codes.
172 */
173static u32 seccomp_run_filters(int syscall)
174{
175 struct seccomp_filter *f;
176 struct seccomp_data sd;
177 u32 ret = SECCOMP_RET_ALLOW;
178
179 /* Ensure unexpected behavior doesn't result in failing open. */
180 if (WARN_ON(current->seccomp.filter == NULL))
181 return SECCOMP_RET_KILL;
182
183 populate_seccomp_data(&sd);
184
185 /*
186 * All filters in the list are evaluated and the lowest BPF return
187 * value always takes priority (ignoring the DATA).
188 */
189 for (f = current->seccomp.filter; f; f = f->prev) {
190 u32 cur_ret = SK_RUN_FILTER(f->prog, (void *)&sd);
191
192 if ((cur_ret & SECCOMP_RET_ACTION) < (ret & SECCOMP_RET_ACTION))
193 ret = cur_ret;
194 }
195 return ret;
196}
197
198/**
199 * seccomp_attach_filter: Attaches a seccomp filter to current.
200 * @fprog: BPF program to install
201 *
202 * Returns 0 on success or an errno on failure.
203 */
204static long seccomp_attach_filter(struct sock_fprog *fprog)
205{
206 struct seccomp_filter *filter;
207 unsigned long fp_size = fprog->len * sizeof(struct sock_filter);
208 unsigned long total_insns = fprog->len;
209 struct sock_filter *fp;
210 int new_len;
211 long ret;
212
213 if (fprog->len == 0 || fprog->len > BPF_MAXINSNS)
214 return -EINVAL;
215
216 for (filter = current->seccomp.filter; filter; filter = filter->prev)
217 total_insns += filter->prog->len + 4; /* include a 4 instr penalty */
218 if (total_insns > MAX_INSNS_PER_PATH)
219 return -ENOMEM;
220
221 /*
222 * Installing a seccomp filter requires that the task has
223 * CAP_SYS_ADMIN in its namespace or be running with no_new_privs.
224 * This avoids scenarios where unprivileged tasks can affect the
225 * behavior of privileged children.
226 */
227 if (!current->no_new_privs &&
228 security_capable_noaudit(current_cred(), current_user_ns(),
229 CAP_SYS_ADMIN) != 0)
230 return -EACCES;
231
232 fp = kzalloc(fp_size, GFP_KERNEL|__GFP_NOWARN);
233 if (!fp)
234 return -ENOMEM;
235
236 /* Copy the instructions from fprog. */
237 ret = -EFAULT;
238 if (copy_from_user(fp, fprog->filter, fp_size))
239 goto free_prog;
240
241 /* Check and rewrite the fprog via the skb checker */
242 ret = sk_chk_filter(fp, fprog->len);
243 if (ret)
244 goto free_prog;
245
246 /* Check and rewrite the fprog for seccomp use */
247 ret = seccomp_check_filter(fp, fprog->len);
248 if (ret)
249 goto free_prog;
250
251 /* Convert 'sock_filter' insns to 'sock_filter_int' insns */
252 ret = sk_convert_filter(fp, fprog->len, NULL, &new_len);
253 if (ret)
254 goto free_prog;
255
256 /* Allocate a new seccomp_filter */
257 ret = -ENOMEM;
258 filter = kzalloc(sizeof(struct seccomp_filter),
259 GFP_KERNEL|__GFP_NOWARN);
260 if (!filter)
261 goto free_prog;
262
263 filter->prog = kzalloc(sk_filter_size(new_len),
264 GFP_KERNEL|__GFP_NOWARN);
265 if (!filter->prog)
266 goto free_filter;
267
268 ret = sk_convert_filter(fp, fprog->len, filter->prog->insnsi, &new_len);
269 if (ret)
270 goto free_filter_prog;
271 kfree(fp);
272
273 atomic_set(&filter->usage, 1);
274 filter->prog->len = new_len;
275
276 sk_filter_select_runtime(filter->prog);
277
278 /*
279 * If there is an existing filter, make it the prev and don't drop its
280 * task reference.
281 */
282 filter->prev = current->seccomp.filter;
283 current->seccomp.filter = filter;
284 return 0;
285
286free_filter_prog:
287 kfree(filter->prog);
288free_filter:
289 kfree(filter);
290free_prog:
291 kfree(fp);
292 return ret;
293}
294
295/**
296 * seccomp_attach_user_filter - attaches a user-supplied sock_fprog
297 * @user_filter: pointer to the user data containing a sock_fprog.
298 *
299 * Returns 0 on success and non-zero otherwise.
300 */
301static long seccomp_attach_user_filter(char __user *user_filter)
302{
303 struct sock_fprog fprog;
304 long ret = -EFAULT;
305
306#ifdef CONFIG_COMPAT
307 if (is_compat_task()) {
308 struct compat_sock_fprog fprog32;
309 if (copy_from_user(&fprog32, user_filter, sizeof(fprog32)))
310 goto out;
311 fprog.len = fprog32.len;
312 fprog.filter = compat_ptr(fprog32.filter);
313 } else /* falls through to the if below. */
314#endif
315 if (copy_from_user(&fprog, user_filter, sizeof(fprog)))
316 goto out;
317 ret = seccomp_attach_filter(&fprog);
318out:
319 return ret;
320}
321
322/* get_seccomp_filter - increments the reference count of the filter on @tsk */
323void get_seccomp_filter(struct task_struct *tsk)
324{
325 struct seccomp_filter *orig = tsk->seccomp.filter;
326 if (!orig)
327 return;
328 /* Reference count is bounded by the number of total processes. */
329 atomic_inc(&orig->usage);
330}
331
332/* put_seccomp_filter - decrements the ref count of tsk->seccomp.filter */
333void put_seccomp_filter(struct task_struct *tsk)
334{
335 struct seccomp_filter *orig = tsk->seccomp.filter;
336 /* Clean up single-reference branches iteratively. */
337 while (orig && atomic_dec_and_test(&orig->usage)) {
338 struct seccomp_filter *freeme = orig;
339 orig = orig->prev;
340 sk_filter_free(freeme->prog);
341 kfree(freeme);
342 }
343}
344
345/**
346 * seccomp_send_sigsys - signals the task to allow in-process syscall emulation
347 * @syscall: syscall number to send to userland
348 * @reason: filter-supplied reason code to send to userland (via si_errno)
349 *
350 * Forces a SIGSYS with a code of SYS_SECCOMP and related sigsys info.
351 */
352static void seccomp_send_sigsys(int syscall, int reason)
353{
354 struct siginfo info;
355 memset(&info, 0, sizeof(info));
356 info.si_signo = SIGSYS;
357 info.si_code = SYS_SECCOMP;
358 info.si_call_addr = (void __user *)KSTK_EIP(current);
359 info.si_errno = reason;
360 info.si_arch = syscall_get_arch();
361 info.si_syscall = syscall;
362 force_sig_info(SIGSYS, &info, current);
363}
364#endif /* CONFIG_SECCOMP_FILTER */
365
366/*
367 * Secure computing mode 1 allows only read/write/exit/sigreturn.
368 * To be fully secure this must be combined with rlimit
369 * to limit the stack allocations too.
370 */
371static int mode1_syscalls[] = {
372 __NR_seccomp_read, __NR_seccomp_write, __NR_seccomp_exit, __NR_seccomp_sigreturn,
373 0, /* null terminated */
374};
375
376#ifdef CONFIG_COMPAT
377static int mode1_syscalls_32[] = {
378 __NR_seccomp_read_32, __NR_seccomp_write_32, __NR_seccomp_exit_32, __NR_seccomp_sigreturn_32,
379 0, /* null terminated */
380};
381#endif
382
383int __secure_computing(int this_syscall)
384{
385 int mode = current->seccomp.mode;
386 int exit_sig = 0;
387 int *syscall;
388 u32 ret;
389
390 switch (mode) {
391 case SECCOMP_MODE_STRICT:
392 syscall = mode1_syscalls;
393#ifdef CONFIG_COMPAT
394 if (is_compat_task())
395 syscall = mode1_syscalls_32;
396#endif
397 do {
398 if (*syscall == this_syscall)
399 return 0;
400 } while (*++syscall);
401 exit_sig = SIGKILL;
402 ret = SECCOMP_RET_KILL;
403 break;
404#ifdef CONFIG_SECCOMP_FILTER
405 case SECCOMP_MODE_FILTER: {
406 int data;
407 struct pt_regs *regs = task_pt_regs(current);
408 ret = seccomp_run_filters(this_syscall);
409 data = ret & SECCOMP_RET_DATA;
410 ret &= SECCOMP_RET_ACTION;
411 switch (ret) {
412 case SECCOMP_RET_ERRNO:
413 /* Set the low-order 16-bits as a errno. */
414 syscall_set_return_value(current, regs,
415 -data, 0);
416 goto skip;
417 case SECCOMP_RET_TRAP:
418 /* Show the handler the original registers. */
419 syscall_rollback(current, regs);
420 /* Let the filter pass back 16 bits of data. */
421 seccomp_send_sigsys(this_syscall, data);
422 goto skip;
423 case SECCOMP_RET_TRACE:
424 /* Skip these calls if there is no tracer. */
425 if (!ptrace_event_enabled(current, PTRACE_EVENT_SECCOMP)) {
426 syscall_set_return_value(current, regs,
427 -ENOSYS, 0);
428 goto skip;
429 }
430 /* Allow the BPF to provide the event message */
431 ptrace_event(PTRACE_EVENT_SECCOMP, data);
432 /*
433 * The delivery of a fatal signal during event
434 * notification may silently skip tracer notification.
435 * Terminating the task now avoids executing a system
436 * call that may not be intended.
437 */
438 if (fatal_signal_pending(current))
439 break;
440 if (syscall_get_nr(current, regs) < 0)
441 goto skip; /* Explicit request to skip. */
442
443 return 0;
444 case SECCOMP_RET_ALLOW:
445 return 0;
446 case SECCOMP_RET_KILL:
447 default:
448 break;
449 }
450 exit_sig = SIGSYS;
451 break;
452 }
453#endif
454 default:
455 BUG();
456 }
457
458#ifdef SECCOMP_DEBUG
459 dump_stack();
460#endif
461 audit_seccomp(this_syscall, exit_sig, ret);
462 do_exit(exit_sig);
463#ifdef CONFIG_SECCOMP_FILTER
464skip:
465 audit_seccomp(this_syscall, exit_sig, ret);
466#endif
467 return -1;
468}
469
470long prctl_get_seccomp(void)
471{
472 return current->seccomp.mode;
473}
474
475/**
476 * prctl_set_seccomp: configures current->seccomp.mode
477 * @seccomp_mode: requested mode to use
478 * @filter: optional struct sock_fprog for use with SECCOMP_MODE_FILTER
479 *
480 * This function may be called repeatedly with a @seccomp_mode of
481 * SECCOMP_MODE_FILTER to install additional filters. Every filter
482 * successfully installed will be evaluated (in reverse order) for each system
483 * call the task makes.
484 *
485 * Once current->seccomp.mode is non-zero, it may not be changed.
486 *
487 * Returns 0 on success or -EINVAL on failure.
488 */
489long prctl_set_seccomp(unsigned long seccomp_mode, char __user *filter)
490{
491 long ret = -EINVAL;
492
493 if (current->seccomp.mode &&
494 current->seccomp.mode != seccomp_mode)
495 goto out;
496
497 switch (seccomp_mode) {
498 case SECCOMP_MODE_STRICT:
499 ret = 0;
500#ifdef TIF_NOTSC
501 disable_TSC();
502#endif
503 break;
504#ifdef CONFIG_SECCOMP_FILTER
505 case SECCOMP_MODE_FILTER:
506 ret = seccomp_attach_user_filter(filter);
507 if (ret)
508 goto out;
509 break;
510#endif
511 default:
512 goto out;
513 }
514
515 current->seccomp.mode = seccomp_mode;
516 set_thread_flag(TIF_SECCOMP);
517out:
518 return ret;
519}