Merge tag 'gpio-v3.13-3' of git://git.kernel.org/pub/scm/linux/kernel/git/linusw...
[linux-2.6.git] / kernel / seccomp.c
blobb7a10048a32c11fb473515d9075ef2b0782a563a
1 /*
2 * linux/kernel/seccomp.c
4 * Copyright 2004-2005 Andrea Arcangeli <andrea@cpushare.com>
6 * Copyright (C) 2012 Google, Inc.
7 * Will Drewry <wad@chromium.org>
9 * This defines a simple but solid secure-computing facility.
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.
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>
22 /* #define SECCOMP_DEBUG 1 */
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>
33 /**
34 * struct seccomp_filter - container for seccomp BPF programs
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 * @insns: the BPF program instructions to evaluate
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.
51 * seccomp_filter objects should never be modified after being attached
52 * to a task_struct (other than @usage).
54 struct seccomp_filter {
55 atomic_t usage;
56 struct seccomp_filter *prev;
57 unsigned short len; /* Instruction count */
58 struct sock_filter insns[];
61 /* Limit any path through the tree to 256KB worth of instructions. */
62 #define MAX_INSNS_PER_PATH ((1 << 18) / sizeof(struct sock_filter))
64 /**
65 * get_u32 - returns a u32 offset into data
66 * @data: a unsigned 64 bit value
67 * @index: 0 or 1 to return the first or second 32-bits
69 * This inline exists to hide the length of unsigned long. If a 32-bit
70 * unsigned long is passed in, it will be extended and the top 32-bits will be
71 * 0. If it is a 64-bit unsigned long, then whatever data is resident will be
72 * properly returned.
74 * Endianness is explicitly ignored and left for BPF program authors to manage
75 * as per the specific architecture.
77 static inline u32 get_u32(u64 data, int index)
79 return ((u32 *)&data)[index];
82 /* Helper for bpf_load below. */
83 #define BPF_DATA(_name) offsetof(struct seccomp_data, _name)
84 /**
85 * bpf_load: checks and returns a pointer to the requested offset
86 * @off: offset into struct seccomp_data to load from
88 * Returns the requested 32-bits of data.
89 * seccomp_check_filter() should assure that @off is 32-bit aligned
90 * and not out of bounds. Failure to do so is a BUG.
92 u32 seccomp_bpf_load(int off)
94 struct pt_regs *regs = task_pt_regs(current);
95 if (off == BPF_DATA(nr))
96 return syscall_get_nr(current, regs);
97 if (off == BPF_DATA(arch))
98 return syscall_get_arch(current, regs);
99 if (off >= BPF_DATA(args[0]) && off < BPF_DATA(args[6])) {
100 unsigned long value;
101 int arg = (off - BPF_DATA(args[0])) / sizeof(u64);
102 int index = !!(off % sizeof(u64));
103 syscall_get_arguments(current, regs, arg, 1, &value);
104 return get_u32(value, index);
106 if (off == BPF_DATA(instruction_pointer))
107 return get_u32(KSTK_EIP(current), 0);
108 if (off == BPF_DATA(instruction_pointer) + sizeof(u32))
109 return get_u32(KSTK_EIP(current), 1);
110 /* seccomp_check_filter should make this impossible. */
111 BUG();
115 * seccomp_check_filter - verify seccomp filter code
116 * @filter: filter to verify
117 * @flen: length of filter
119 * Takes a previously checked filter (by sk_chk_filter) and
120 * redirects all filter code that loads struct sk_buff data
121 * and related data through seccomp_bpf_load. It also
122 * enforces length and alignment checking of those loads.
124 * Returns 0 if the rule set is legal or -EINVAL if not.
126 static int seccomp_check_filter(struct sock_filter *filter, unsigned int flen)
128 int pc;
129 for (pc = 0; pc < flen; pc++) {
130 struct sock_filter *ftest = &filter[pc];
131 u16 code = ftest->code;
132 u32 k = ftest->k;
134 switch (code) {
135 case BPF_S_LD_W_ABS:
136 ftest->code = BPF_S_ANC_SECCOMP_LD_W;
137 /* 32-bit aligned and not out of bounds. */
138 if (k >= sizeof(struct seccomp_data) || k & 3)
139 return -EINVAL;
140 continue;
141 case BPF_S_LD_W_LEN:
142 ftest->code = BPF_S_LD_IMM;
143 ftest->k = sizeof(struct seccomp_data);
144 continue;
145 case BPF_S_LDX_W_LEN:
146 ftest->code = BPF_S_LDX_IMM;
147 ftest->k = sizeof(struct seccomp_data);
148 continue;
149 /* Explicitly include allowed calls. */
150 case BPF_S_RET_K:
151 case BPF_S_RET_A:
152 case BPF_S_ALU_ADD_K:
153 case BPF_S_ALU_ADD_X:
154 case BPF_S_ALU_SUB_K:
155 case BPF_S_ALU_SUB_X:
156 case BPF_S_ALU_MUL_K:
157 case BPF_S_ALU_MUL_X:
158 case BPF_S_ALU_DIV_X:
159 case BPF_S_ALU_AND_K:
160 case BPF_S_ALU_AND_X:
161 case BPF_S_ALU_OR_K:
162 case BPF_S_ALU_OR_X:
163 case BPF_S_ALU_XOR_K:
164 case BPF_S_ALU_XOR_X:
165 case BPF_S_ALU_LSH_K:
166 case BPF_S_ALU_LSH_X:
167 case BPF_S_ALU_RSH_K:
168 case BPF_S_ALU_RSH_X:
169 case BPF_S_ALU_NEG:
170 case BPF_S_LD_IMM:
171 case BPF_S_LDX_IMM:
172 case BPF_S_MISC_TAX:
173 case BPF_S_MISC_TXA:
174 case BPF_S_ALU_DIV_K:
175 case BPF_S_LD_MEM:
176 case BPF_S_LDX_MEM:
177 case BPF_S_ST:
178 case BPF_S_STX:
179 case BPF_S_JMP_JA:
180 case BPF_S_JMP_JEQ_K:
181 case BPF_S_JMP_JEQ_X:
182 case BPF_S_JMP_JGE_K:
183 case BPF_S_JMP_JGE_X:
184 case BPF_S_JMP_JGT_K:
185 case BPF_S_JMP_JGT_X:
186 case BPF_S_JMP_JSET_K:
187 case BPF_S_JMP_JSET_X:
188 continue;
189 default:
190 return -EINVAL;
193 return 0;
197 * seccomp_run_filters - evaluates all seccomp filters against @syscall
198 * @syscall: number of the current system call
200 * Returns valid seccomp BPF response codes.
202 static u32 seccomp_run_filters(int syscall)
204 struct seccomp_filter *f;
205 u32 ret = SECCOMP_RET_ALLOW;
207 /* Ensure unexpected behavior doesn't result in failing open. */
208 if (WARN_ON(current->seccomp.filter == NULL))
209 return SECCOMP_RET_KILL;
212 * All filters in the list are evaluated and the lowest BPF return
213 * value always takes priority (ignoring the DATA).
215 for (f = current->seccomp.filter; f; f = f->prev) {
216 u32 cur_ret = sk_run_filter(NULL, f->insns);
217 if ((cur_ret & SECCOMP_RET_ACTION) < (ret & SECCOMP_RET_ACTION))
218 ret = cur_ret;
220 return ret;
224 * seccomp_attach_filter: Attaches a seccomp filter to current.
225 * @fprog: BPF program to install
227 * Returns 0 on success or an errno on failure.
229 static long seccomp_attach_filter(struct sock_fprog *fprog)
231 struct seccomp_filter *filter;
232 unsigned long fp_size = fprog->len * sizeof(struct sock_filter);
233 unsigned long total_insns = fprog->len;
234 long ret;
236 if (fprog->len == 0 || fprog->len > BPF_MAXINSNS)
237 return -EINVAL;
239 for (filter = current->seccomp.filter; filter; filter = filter->prev)
240 total_insns += filter->len + 4; /* include a 4 instr penalty */
241 if (total_insns > MAX_INSNS_PER_PATH)
242 return -ENOMEM;
245 * Installing a seccomp filter requires that the task have
246 * CAP_SYS_ADMIN in its namespace or be running with no_new_privs.
247 * This avoids scenarios where unprivileged tasks can affect the
248 * behavior of privileged children.
250 if (!current->no_new_privs &&
251 security_capable_noaudit(current_cred(), current_user_ns(),
252 CAP_SYS_ADMIN) != 0)
253 return -EACCES;
255 /* Allocate a new seccomp_filter */
256 filter = kzalloc(sizeof(struct seccomp_filter) + fp_size,
257 GFP_KERNEL|__GFP_NOWARN);
258 if (!filter)
259 return -ENOMEM;
260 atomic_set(&filter->usage, 1);
261 filter->len = fprog->len;
263 /* Copy the instructions from fprog. */
264 ret = -EFAULT;
265 if (copy_from_user(filter->insns, fprog->filter, fp_size))
266 goto fail;
268 /* Check and rewrite the fprog via the skb checker */
269 ret = sk_chk_filter(filter->insns, filter->len);
270 if (ret)
271 goto fail;
273 /* Check and rewrite the fprog for seccomp use */
274 ret = seccomp_check_filter(filter->insns, filter->len);
275 if (ret)
276 goto fail;
279 * If there is an existing filter, make it the prev and don't drop its
280 * task reference.
282 filter->prev = current->seccomp.filter;
283 current->seccomp.filter = filter;
284 return 0;
285 fail:
286 kfree(filter);
287 return ret;
291 * seccomp_attach_user_filter - attaches a user-supplied sock_fprog
292 * @user_filter: pointer to the user data containing a sock_fprog.
294 * Returns 0 on success and non-zero otherwise.
296 long seccomp_attach_user_filter(char __user *user_filter)
298 struct sock_fprog fprog;
299 long ret = -EFAULT;
301 #ifdef CONFIG_COMPAT
302 if (is_compat_task()) {
303 struct compat_sock_fprog fprog32;
304 if (copy_from_user(&fprog32, user_filter, sizeof(fprog32)))
305 goto out;
306 fprog.len = fprog32.len;
307 fprog.filter = compat_ptr(fprog32.filter);
308 } else /* falls through to the if below. */
309 #endif
310 if (copy_from_user(&fprog, user_filter, sizeof(fprog)))
311 goto out;
312 ret = seccomp_attach_filter(&fprog);
313 out:
314 return ret;
317 /* get_seccomp_filter - increments the reference count of the filter on @tsk */
318 void get_seccomp_filter(struct task_struct *tsk)
320 struct seccomp_filter *orig = tsk->seccomp.filter;
321 if (!orig)
322 return;
323 /* Reference count is bounded by the number of total processes. */
324 atomic_inc(&orig->usage);
327 /* put_seccomp_filter - decrements the ref count of tsk->seccomp.filter */
328 void put_seccomp_filter(struct task_struct *tsk)
330 struct seccomp_filter *orig = tsk->seccomp.filter;
331 /* Clean up single-reference branches iteratively. */
332 while (orig && atomic_dec_and_test(&orig->usage)) {
333 struct seccomp_filter *freeme = orig;
334 orig = orig->prev;
335 kfree(freeme);
340 * seccomp_send_sigsys - signals the task to allow in-process syscall emulation
341 * @syscall: syscall number to send to userland
342 * @reason: filter-supplied reason code to send to userland (via si_errno)
344 * Forces a SIGSYS with a code of SYS_SECCOMP and related sigsys info.
346 static void seccomp_send_sigsys(int syscall, int reason)
348 struct siginfo info;
349 memset(&info, 0, sizeof(info));
350 info.si_signo = SIGSYS;
351 info.si_code = SYS_SECCOMP;
352 info.si_call_addr = (void __user *)KSTK_EIP(current);
353 info.si_errno = reason;
354 info.si_arch = syscall_get_arch(current, task_pt_regs(current));
355 info.si_syscall = syscall;
356 force_sig_info(SIGSYS, &info, current);
358 #endif /* CONFIG_SECCOMP_FILTER */
361 * Secure computing mode 1 allows only read/write/exit/sigreturn.
362 * To be fully secure this must be combined with rlimit
363 * to limit the stack allocations too.
365 static int mode1_syscalls[] = {
366 __NR_seccomp_read, __NR_seccomp_write, __NR_seccomp_exit, __NR_seccomp_sigreturn,
367 0, /* null terminated */
370 #ifdef CONFIG_COMPAT
371 static int mode1_syscalls_32[] = {
372 __NR_seccomp_read_32, __NR_seccomp_write_32, __NR_seccomp_exit_32, __NR_seccomp_sigreturn_32,
373 0, /* null terminated */
375 #endif
377 int __secure_computing(int this_syscall)
379 int mode = current->seccomp.mode;
380 int exit_sig = 0;
381 int *syscall;
382 u32 ret;
384 switch (mode) {
385 case SECCOMP_MODE_STRICT:
386 syscall = mode1_syscalls;
387 #ifdef CONFIG_COMPAT
388 if (is_compat_task())
389 syscall = mode1_syscalls_32;
390 #endif
391 do {
392 if (*syscall == this_syscall)
393 return 0;
394 } while (*++syscall);
395 exit_sig = SIGKILL;
396 ret = SECCOMP_RET_KILL;
397 break;
398 #ifdef CONFIG_SECCOMP_FILTER
399 case SECCOMP_MODE_FILTER: {
400 int data;
401 struct pt_regs *regs = task_pt_regs(current);
402 ret = seccomp_run_filters(this_syscall);
403 data = ret & SECCOMP_RET_DATA;
404 ret &= SECCOMP_RET_ACTION;
405 switch (ret) {
406 case SECCOMP_RET_ERRNO:
407 /* Set the low-order 16-bits as a errno. */
408 syscall_set_return_value(current, regs,
409 -data, 0);
410 goto skip;
411 case SECCOMP_RET_TRAP:
412 /* Show the handler the original registers. */
413 syscall_rollback(current, regs);
414 /* Let the filter pass back 16 bits of data. */
415 seccomp_send_sigsys(this_syscall, data);
416 goto skip;
417 case SECCOMP_RET_TRACE:
418 /* Skip these calls if there is no tracer. */
419 if (!ptrace_event_enabled(current, PTRACE_EVENT_SECCOMP)) {
420 syscall_set_return_value(current, regs,
421 -ENOSYS, 0);
422 goto skip;
424 /* Allow the BPF to provide the event message */
425 ptrace_event(PTRACE_EVENT_SECCOMP, data);
427 * The delivery of a fatal signal during event
428 * notification may silently skip tracer notification.
429 * Terminating the task now avoids executing a system
430 * call that may not be intended.
432 if (fatal_signal_pending(current))
433 break;
434 if (syscall_get_nr(current, regs) < 0)
435 goto skip; /* Explicit request to skip. */
437 return 0;
438 case SECCOMP_RET_ALLOW:
439 return 0;
440 case SECCOMP_RET_KILL:
441 default:
442 break;
444 exit_sig = SIGSYS;
445 break;
447 #endif
448 default:
449 BUG();
452 #ifdef SECCOMP_DEBUG
453 dump_stack();
454 #endif
455 audit_seccomp(this_syscall, exit_sig, ret);
456 do_exit(exit_sig);
457 #ifdef CONFIG_SECCOMP_FILTER
458 skip:
459 audit_seccomp(this_syscall, exit_sig, ret);
460 #endif
461 return -1;
464 long prctl_get_seccomp(void)
466 return current->seccomp.mode;
470 * prctl_set_seccomp: configures current->seccomp.mode
471 * @seccomp_mode: requested mode to use
472 * @filter: optional struct sock_fprog for use with SECCOMP_MODE_FILTER
474 * This function may be called repeatedly with a @seccomp_mode of
475 * SECCOMP_MODE_FILTER to install additional filters. Every filter
476 * successfully installed will be evaluated (in reverse order) for each system
477 * call the task makes.
479 * Once current->seccomp.mode is non-zero, it may not be changed.
481 * Returns 0 on success or -EINVAL on failure.
483 long prctl_set_seccomp(unsigned long seccomp_mode, char __user *filter)
485 long ret = -EINVAL;
487 if (current->seccomp.mode &&
488 current->seccomp.mode != seccomp_mode)
489 goto out;
491 switch (seccomp_mode) {
492 case SECCOMP_MODE_STRICT:
493 ret = 0;
494 #ifdef TIF_NOTSC
495 disable_TSC();
496 #endif
497 break;
498 #ifdef CONFIG_SECCOMP_FILTER
499 case SECCOMP_MODE_FILTER:
500 ret = seccomp_attach_user_filter(filter);
501 if (ret)
502 goto out;
503 break;
504 #endif
505 default:
506 goto out;
509 current->seccomp.mode = seccomp_mode;
510 set_thread_flag(TIF_SECCOMP);
511 out:
512 return ret;