Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jmorris...
[sfrench/cifs-2.6.git] / 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
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  * @insns: 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  */
54 struct seccomp_filter {
55         atomic_t usage;
56         struct seccomp_filter *prev;
57         unsigned short len;  /* Instruction count */
58         struct sock_filter_int insnsi[];
59 };
60
61 /* Limit any path through the tree to 256KB worth of instructions. */
62 #define MAX_INSNS_PER_PATH ((1 << 18) / sizeof(struct sock_filter))
63
64 /*
65  * Endianness is explicitly ignored and left for BPF program authors to manage
66  * as per the specific architecture.
67  */
68 static void populate_seccomp_data(struct seccomp_data *sd)
69 {
70         struct task_struct *task = current;
71         struct pt_regs *regs = task_pt_regs(task);
72
73         sd->nr = syscall_get_nr(task, regs);
74         sd->arch = syscall_get_arch(task, regs);
75
76         /* Unroll syscall_get_args to help gcc on arm. */
77         syscall_get_arguments(task, regs, 0, 1, (unsigned long *) &sd->args[0]);
78         syscall_get_arguments(task, regs, 1, 1, (unsigned long *) &sd->args[1]);
79         syscall_get_arguments(task, regs, 2, 1, (unsigned long *) &sd->args[2]);
80         syscall_get_arguments(task, regs, 3, 1, (unsigned long *) &sd->args[3]);
81         syscall_get_arguments(task, regs, 4, 1, (unsigned long *) &sd->args[4]);
82         syscall_get_arguments(task, regs, 5, 1, (unsigned long *) &sd->args[5]);
83
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 sk_chk_filter) 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_S_LD_W_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_S_LD_W_LEN:
115                         ftest->code = BPF_LD | BPF_IMM;
116                         ftest->k = sizeof(struct seccomp_data);
117                         continue;
118                 case BPF_S_LDX_W_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_S_RET_K:
124                 case BPF_S_RET_A:
125                 case BPF_S_ALU_ADD_K:
126                 case BPF_S_ALU_ADD_X:
127                 case BPF_S_ALU_SUB_K:
128                 case BPF_S_ALU_SUB_X:
129                 case BPF_S_ALU_MUL_K:
130                 case BPF_S_ALU_MUL_X:
131                 case BPF_S_ALU_DIV_X:
132                 case BPF_S_ALU_AND_K:
133                 case BPF_S_ALU_AND_X:
134                 case BPF_S_ALU_OR_K:
135                 case BPF_S_ALU_OR_X:
136                 case BPF_S_ALU_XOR_K:
137                 case BPF_S_ALU_XOR_X:
138                 case BPF_S_ALU_LSH_K:
139                 case BPF_S_ALU_LSH_X:
140                 case BPF_S_ALU_RSH_K:
141                 case BPF_S_ALU_RSH_X:
142                 case BPF_S_ALU_NEG:
143                 case BPF_S_LD_IMM:
144                 case BPF_S_LDX_IMM:
145                 case BPF_S_MISC_TAX:
146                 case BPF_S_MISC_TXA:
147                 case BPF_S_ALU_DIV_K:
148                 case BPF_S_LD_MEM:
149                 case BPF_S_LDX_MEM:
150                 case BPF_S_ST:
151                 case BPF_S_STX:
152                 case BPF_S_JMP_JA:
153                 case BPF_S_JMP_JEQ_K:
154                 case BPF_S_JMP_JEQ_X:
155                 case BPF_S_JMP_JGE_K:
156                 case BPF_S_JMP_JGE_X:
157                 case BPF_S_JMP_JGT_K:
158                 case BPF_S_JMP_JGT_X:
159                 case BPF_S_JMP_JSET_K:
160                 case BPF_S_JMP_JSET_X:
161                         sk_decode_filter(ftest, ftest);
162                         continue;
163                 default:
164                         return -EINVAL;
165                 }
166         }
167         return 0;
168 }
169
170 /**
171  * seccomp_run_filters - evaluates all seccomp filters against @syscall
172  * @syscall: number of the current system call
173  *
174  * Returns valid seccomp BPF response codes.
175  */
176 static u32 seccomp_run_filters(int syscall)
177 {
178         struct seccomp_filter *f;
179         struct seccomp_data sd;
180         u32 ret = SECCOMP_RET_ALLOW;
181
182         /* Ensure unexpected behavior doesn't result in failing open. */
183         if (WARN_ON(current->seccomp.filter == NULL))
184                 return SECCOMP_RET_KILL;
185
186         populate_seccomp_data(&sd);
187
188         /*
189          * All filters in the list are evaluated and the lowest BPF return
190          * value always takes priority (ignoring the DATA).
191          */
192         for (f = current->seccomp.filter; f; f = f->prev) {
193                 u32 cur_ret = sk_run_filter_int_seccomp(&sd, f->insnsi);
194                 if ((cur_ret & SECCOMP_RET_ACTION) < (ret & SECCOMP_RET_ACTION))
195                         ret = cur_ret;
196         }
197         return ret;
198 }
199
200 /**
201  * seccomp_attach_filter: Attaches a seccomp filter to current.
202  * @fprog: BPF program to install
203  *
204  * Returns 0 on success or an errno on failure.
205  */
206 static long seccomp_attach_filter(struct sock_fprog *fprog)
207 {
208         struct seccomp_filter *filter;
209         unsigned long fp_size = fprog->len * sizeof(struct sock_filter);
210         unsigned long total_insns = fprog->len;
211         struct sock_filter *fp;
212         int new_len;
213         long ret;
214
215         if (fprog->len == 0 || fprog->len > BPF_MAXINSNS)
216                 return -EINVAL;
217
218         for (filter = current->seccomp.filter; filter; filter = filter->prev)
219                 total_insns += filter->len + 4;  /* include a 4 instr penalty */
220         if (total_insns > MAX_INSNS_PER_PATH)
221                 return -ENOMEM;
222
223         /*
224          * Installing a seccomp filter requires that the task have
225          * CAP_SYS_ADMIN in its namespace or be running with no_new_privs.
226          * This avoids scenarios where unprivileged tasks can affect the
227          * behavior of privileged children.
228          */
229         if (!current->no_new_privs &&
230             security_capable_noaudit(current_cred(), current_user_ns(),
231                                      CAP_SYS_ADMIN) != 0)
232                 return -EACCES;
233
234         fp = kzalloc(fp_size, GFP_KERNEL|__GFP_NOWARN);
235         if (!fp)
236                 return -ENOMEM;
237
238         /* Copy the instructions from fprog. */
239         ret = -EFAULT;
240         if (copy_from_user(fp, fprog->filter, fp_size))
241                 goto free_prog;
242
243         /* Check and rewrite the fprog via the skb checker */
244         ret = sk_chk_filter(fp, fprog->len);
245         if (ret)
246                 goto free_prog;
247
248         /* Check and rewrite the fprog for seccomp use */
249         ret = seccomp_check_filter(fp, fprog->len);
250         if (ret)
251                 goto free_prog;
252
253         /* Convert 'sock_filter' insns to 'sock_filter_int' insns */
254         ret = sk_convert_filter(fp, fprog->len, NULL, &new_len);
255         if (ret)
256                 goto free_prog;
257
258         /* Allocate a new seccomp_filter */
259         filter = kzalloc(sizeof(struct seccomp_filter) +
260                          sizeof(struct sock_filter_int) * new_len,
261                          GFP_KERNEL|__GFP_NOWARN);
262         if (!filter)
263                 goto free_prog;
264
265         ret = sk_convert_filter(fp, fprog->len, filter->insnsi, &new_len);
266         if (ret)
267                 goto free_filter;
268
269         atomic_set(&filter->usage, 1);
270         filter->len = new_len;
271
272         /*
273          * If there is an existing filter, make it the prev and don't drop its
274          * task reference.
275          */
276         filter->prev = current->seccomp.filter;
277         current->seccomp.filter = filter;
278         return 0;
279
280 free_filter:
281         kfree(filter);
282 free_prog:
283         kfree(fp);
284         return ret;
285 }
286
287 /**
288  * seccomp_attach_user_filter - attaches a user-supplied sock_fprog
289  * @user_filter: pointer to the user data containing a sock_fprog.
290  *
291  * Returns 0 on success and non-zero otherwise.
292  */
293 static long seccomp_attach_user_filter(char __user *user_filter)
294 {
295         struct sock_fprog fprog;
296         long ret = -EFAULT;
297
298 #ifdef CONFIG_COMPAT
299         if (is_compat_task()) {
300                 struct compat_sock_fprog fprog32;
301                 if (copy_from_user(&fprog32, user_filter, sizeof(fprog32)))
302                         goto out;
303                 fprog.len = fprog32.len;
304                 fprog.filter = compat_ptr(fprog32.filter);
305         } else /* falls through to the if below. */
306 #endif
307         if (copy_from_user(&fprog, user_filter, sizeof(fprog)))
308                 goto out;
309         ret = seccomp_attach_filter(&fprog);
310 out:
311         return ret;
312 }
313
314 /* get_seccomp_filter - increments the reference count of the filter on @tsk */
315 void get_seccomp_filter(struct task_struct *tsk)
316 {
317         struct seccomp_filter *orig = tsk->seccomp.filter;
318         if (!orig)
319                 return;
320         /* Reference count is bounded by the number of total processes. */
321         atomic_inc(&orig->usage);
322 }
323
324 /* put_seccomp_filter - decrements the ref count of tsk->seccomp.filter */
325 void put_seccomp_filter(struct task_struct *tsk)
326 {
327         struct seccomp_filter *orig = tsk->seccomp.filter;
328         /* Clean up single-reference branches iteratively. */
329         while (orig && atomic_dec_and_test(&orig->usage)) {
330                 struct seccomp_filter *freeme = orig;
331                 orig = orig->prev;
332                 kfree(freeme);
333         }
334 }
335
336 /**
337  * seccomp_send_sigsys - signals the task to allow in-process syscall emulation
338  * @syscall: syscall number to send to userland
339  * @reason: filter-supplied reason code to send to userland (via si_errno)
340  *
341  * Forces a SIGSYS with a code of SYS_SECCOMP and related sigsys info.
342  */
343 static void seccomp_send_sigsys(int syscall, int reason)
344 {
345         struct siginfo info;
346         memset(&info, 0, sizeof(info));
347         info.si_signo = SIGSYS;
348         info.si_code = SYS_SECCOMP;
349         info.si_call_addr = (void __user *)KSTK_EIP(current);
350         info.si_errno = reason;
351         info.si_arch = syscall_get_arch(current, task_pt_regs(current));
352         info.si_syscall = syscall;
353         force_sig_info(SIGSYS, &info, current);
354 }
355 #endif  /* CONFIG_SECCOMP_FILTER */
356
357 /*
358  * Secure computing mode 1 allows only read/write/exit/sigreturn.
359  * To be fully secure this must be combined with rlimit
360  * to limit the stack allocations too.
361  */
362 static int mode1_syscalls[] = {
363         __NR_seccomp_read, __NR_seccomp_write, __NR_seccomp_exit, __NR_seccomp_sigreturn,
364         0, /* null terminated */
365 };
366
367 #ifdef CONFIG_COMPAT
368 static int mode1_syscalls_32[] = {
369         __NR_seccomp_read_32, __NR_seccomp_write_32, __NR_seccomp_exit_32, __NR_seccomp_sigreturn_32,
370         0, /* null terminated */
371 };
372 #endif
373
374 int __secure_computing(int this_syscall)
375 {
376         int mode = current->seccomp.mode;
377         int exit_sig = 0;
378         int *syscall;
379         u32 ret;
380
381         switch (mode) {
382         case SECCOMP_MODE_STRICT:
383                 syscall = mode1_syscalls;
384 #ifdef CONFIG_COMPAT
385                 if (is_compat_task())
386                         syscall = mode1_syscalls_32;
387 #endif
388                 do {
389                         if (*syscall == this_syscall)
390                                 return 0;
391                 } while (*++syscall);
392                 exit_sig = SIGKILL;
393                 ret = SECCOMP_RET_KILL;
394                 break;
395 #ifdef CONFIG_SECCOMP_FILTER
396         case SECCOMP_MODE_FILTER: {
397                 int data;
398                 struct pt_regs *regs = task_pt_regs(current);
399                 ret = seccomp_run_filters(this_syscall);
400                 data = ret & SECCOMP_RET_DATA;
401                 ret &= SECCOMP_RET_ACTION;
402                 switch (ret) {
403                 case SECCOMP_RET_ERRNO:
404                         /* Set the low-order 16-bits as a errno. */
405                         syscall_set_return_value(current, regs,
406                                                  -data, 0);
407                         goto skip;
408                 case SECCOMP_RET_TRAP:
409                         /* Show the handler the original registers. */
410                         syscall_rollback(current, regs);
411                         /* Let the filter pass back 16 bits of data. */
412                         seccomp_send_sigsys(this_syscall, data);
413                         goto skip;
414                 case SECCOMP_RET_TRACE:
415                         /* Skip these calls if there is no tracer. */
416                         if (!ptrace_event_enabled(current, PTRACE_EVENT_SECCOMP)) {
417                                 syscall_set_return_value(current, regs,
418                                                          -ENOSYS, 0);
419                                 goto skip;
420                         }
421                         /* Allow the BPF to provide the event message */
422                         ptrace_event(PTRACE_EVENT_SECCOMP, data);
423                         /*
424                          * The delivery of a fatal signal during event
425                          * notification may silently skip tracer notification.
426                          * Terminating the task now avoids executing a system
427                          * call that may not be intended.
428                          */
429                         if (fatal_signal_pending(current))
430                                 break;
431                         if (syscall_get_nr(current, regs) < 0)
432                                 goto skip;  /* Explicit request to skip. */
433
434                         return 0;
435                 case SECCOMP_RET_ALLOW:
436                         return 0;
437                 case SECCOMP_RET_KILL:
438                 default:
439                         break;
440                 }
441                 exit_sig = SIGSYS;
442                 break;
443         }
444 #endif
445         default:
446                 BUG();
447         }
448
449 #ifdef SECCOMP_DEBUG
450         dump_stack();
451 #endif
452         audit_seccomp(this_syscall, exit_sig, ret);
453         do_exit(exit_sig);
454 #ifdef CONFIG_SECCOMP_FILTER
455 skip:
456         audit_seccomp(this_syscall, exit_sig, ret);
457 #endif
458         return -1;
459 }
460
461 long prctl_get_seccomp(void)
462 {
463         return current->seccomp.mode;
464 }
465
466 /**
467  * prctl_set_seccomp: configures current->seccomp.mode
468  * @seccomp_mode: requested mode to use
469  * @filter: optional struct sock_fprog for use with SECCOMP_MODE_FILTER
470  *
471  * This function may be called repeatedly with a @seccomp_mode of
472  * SECCOMP_MODE_FILTER to install additional filters.  Every filter
473  * successfully installed will be evaluated (in reverse order) for each system
474  * call the task makes.
475  *
476  * Once current->seccomp.mode is non-zero, it may not be changed.
477  *
478  * Returns 0 on success or -EINVAL on failure.
479  */
480 long prctl_set_seccomp(unsigned long seccomp_mode, char __user *filter)
481 {
482         long ret = -EINVAL;
483
484         if (current->seccomp.mode &&
485             current->seccomp.mode != seccomp_mode)
486                 goto out;
487
488         switch (seccomp_mode) {
489         case SECCOMP_MODE_STRICT:
490                 ret = 0;
491 #ifdef TIF_NOTSC
492                 disable_TSC();
493 #endif
494                 break;
495 #ifdef CONFIG_SECCOMP_FILTER
496         case SECCOMP_MODE_FILTER:
497                 ret = seccomp_attach_user_filter(filter);
498                 if (ret)
499                         goto out;
500                 break;
501 #endif
502         default:
503                 goto out;
504         }
505
506         current->seccomp.mode = seccomp_mode;
507         set_thread_flag(TIF_SECCOMP);
508 out:
509         return ret;
510 }