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Linux/kernel/bpf/cgroup.c

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  1 /*
  2  * Functions to manage eBPF programs attached to cgroups
  3  *
  4  * Copyright (c) 2016 Daniel Mack
  5  *
  6  * This file is subject to the terms and conditions of version 2 of the GNU
  7  * General Public License.  See the file COPYING in the main directory of the
  8  * Linux distribution for more details.
  9  */
 10 
 11 #include <linux/kernel.h>
 12 #include <linux/atomic.h>
 13 #include <linux/cgroup.h>
 14 #include <linux/slab.h>
 15 #include <linux/bpf.h>
 16 #include <linux/bpf-cgroup.h>
 17 #include <net/sock.h>
 18 
 19 DEFINE_STATIC_KEY_FALSE(cgroup_bpf_enabled_key);
 20 EXPORT_SYMBOL(cgroup_bpf_enabled_key);
 21 
 22 /**
 23  * cgroup_bpf_put() - put references of all bpf programs
 24  * @cgrp: the cgroup to modify
 25  */
 26 void cgroup_bpf_put(struct cgroup *cgrp)
 27 {
 28         unsigned int type;
 29 
 30         for (type = 0; type < ARRAY_SIZE(cgrp->bpf.progs); type++) {
 31                 struct list_head *progs = &cgrp->bpf.progs[type];
 32                 struct bpf_prog_list *pl, *tmp;
 33 
 34                 list_for_each_entry_safe(pl, tmp, progs, node) {
 35                         list_del(&pl->node);
 36                         bpf_prog_put(pl->prog);
 37                         kfree(pl);
 38                         static_branch_dec(&cgroup_bpf_enabled_key);
 39                 }
 40                 bpf_prog_array_free(cgrp->bpf.effective[type]);
 41         }
 42 }
 43 
 44 /* count number of elements in the list.
 45  * it's slow but the list cannot be long
 46  */
 47 static u32 prog_list_length(struct list_head *head)
 48 {
 49         struct bpf_prog_list *pl;
 50         u32 cnt = 0;
 51 
 52         list_for_each_entry(pl, head, node) {
 53                 if (!pl->prog)
 54                         continue;
 55                 cnt++;
 56         }
 57         return cnt;
 58 }
 59 
 60 /* if parent has non-overridable prog attached,
 61  * disallow attaching new programs to the descendent cgroup.
 62  * if parent has overridable or multi-prog, allow attaching
 63  */
 64 static bool hierarchy_allows_attach(struct cgroup *cgrp,
 65                                     enum bpf_attach_type type,
 66                                     u32 new_flags)
 67 {
 68         struct cgroup *p;
 69 
 70         p = cgroup_parent(cgrp);
 71         if (!p)
 72                 return true;
 73         do {
 74                 u32 flags = p->bpf.flags[type];
 75                 u32 cnt;
 76 
 77                 if (flags & BPF_F_ALLOW_MULTI)
 78                         return true;
 79                 cnt = prog_list_length(&p->bpf.progs[type]);
 80                 WARN_ON_ONCE(cnt > 1);
 81                 if (cnt == 1)
 82                         return !!(flags & BPF_F_ALLOW_OVERRIDE);
 83                 p = cgroup_parent(p);
 84         } while (p);
 85         return true;
 86 }
 87 
 88 /* compute a chain of effective programs for a given cgroup:
 89  * start from the list of programs in this cgroup and add
 90  * all parent programs.
 91  * Note that parent's F_ALLOW_OVERRIDE-type program is yielding
 92  * to programs in this cgroup
 93  */
 94 static int compute_effective_progs(struct cgroup *cgrp,
 95                                    enum bpf_attach_type type,
 96                                    struct bpf_prog_array __rcu **array)
 97 {
 98         struct bpf_prog_array __rcu *progs;
 99         struct bpf_prog_list *pl;
100         struct cgroup *p = cgrp;
101         int cnt = 0;
102 
103         /* count number of effective programs by walking parents */
104         do {
105                 if (cnt == 0 || (p->bpf.flags[type] & BPF_F_ALLOW_MULTI))
106                         cnt += prog_list_length(&p->bpf.progs[type]);
107                 p = cgroup_parent(p);
108         } while (p);
109 
110         progs = bpf_prog_array_alloc(cnt, GFP_KERNEL);
111         if (!progs)
112                 return -ENOMEM;
113 
114         /* populate the array with effective progs */
115         cnt = 0;
116         p = cgrp;
117         do {
118                 if (cnt == 0 || (p->bpf.flags[type] & BPF_F_ALLOW_MULTI))
119                         list_for_each_entry(pl,
120                                             &p->bpf.progs[type], node) {
121                                 if (!pl->prog)
122                                         continue;
123                                 rcu_dereference_protected(progs, 1)->
124                                         progs[cnt++] = pl->prog;
125                         }
126                 p = cgroup_parent(p);
127         } while (p);
128 
129         *array = progs;
130         return 0;
131 }
132 
133 static void activate_effective_progs(struct cgroup *cgrp,
134                                      enum bpf_attach_type type,
135                                      struct bpf_prog_array __rcu *array)
136 {
137         struct bpf_prog_array __rcu *old_array;
138 
139         old_array = xchg(&cgrp->bpf.effective[type], array);
140         /* free prog array after grace period, since __cgroup_bpf_run_*()
141          * might be still walking the array
142          */
143         bpf_prog_array_free(old_array);
144 }
145 
146 /**
147  * cgroup_bpf_inherit() - inherit effective programs from parent
148  * @cgrp: the cgroup to modify
149  */
150 int cgroup_bpf_inherit(struct cgroup *cgrp)
151 {
152 /* has to use marco instead of const int, since compiler thinks
153  * that array below is variable length
154  */
155 #define NR ARRAY_SIZE(cgrp->bpf.effective)
156         struct bpf_prog_array __rcu *arrays[NR] = {};
157         int i;
158 
159         for (i = 0; i < NR; i++)
160                 INIT_LIST_HEAD(&cgrp->bpf.progs[i]);
161 
162         for (i = 0; i < NR; i++)
163                 if (compute_effective_progs(cgrp, i, &arrays[i]))
164                         goto cleanup;
165 
166         for (i = 0; i < NR; i++)
167                 activate_effective_progs(cgrp, i, arrays[i]);
168 
169         return 0;
170 cleanup:
171         for (i = 0; i < NR; i++)
172                 bpf_prog_array_free(arrays[i]);
173         return -ENOMEM;
174 }
175 
176 #define BPF_CGROUP_MAX_PROGS 64
177 
178 /**
179  * __cgroup_bpf_attach() - Attach the program to a cgroup, and
180  *                         propagate the change to descendants
181  * @cgrp: The cgroup which descendants to traverse
182  * @prog: A program to attach
183  * @type: Type of attach operation
184  *
185  * Must be called with cgroup_mutex held.
186  */
187 int __cgroup_bpf_attach(struct cgroup *cgrp, struct bpf_prog *prog,
188                         enum bpf_attach_type type, u32 flags)
189 {
190         struct list_head *progs = &cgrp->bpf.progs[type];
191         struct bpf_prog *old_prog = NULL;
192         struct cgroup_subsys_state *css;
193         struct bpf_prog_list *pl;
194         bool pl_was_allocated;
195         int err;
196 
197         if ((flags & BPF_F_ALLOW_OVERRIDE) && (flags & BPF_F_ALLOW_MULTI))
198                 /* invalid combination */
199                 return -EINVAL;
200 
201         if (!hierarchy_allows_attach(cgrp, type, flags))
202                 return -EPERM;
203 
204         if (!list_empty(progs) && cgrp->bpf.flags[type] != flags)
205                 /* Disallow attaching non-overridable on top
206                  * of existing overridable in this cgroup.
207                  * Disallow attaching multi-prog if overridable or none
208                  */
209                 return -EPERM;
210 
211         if (prog_list_length(progs) >= BPF_CGROUP_MAX_PROGS)
212                 return -E2BIG;
213 
214         if (flags & BPF_F_ALLOW_MULTI) {
215                 list_for_each_entry(pl, progs, node)
216                         if (pl->prog == prog)
217                                 /* disallow attaching the same prog twice */
218                                 return -EINVAL;
219 
220                 pl = kmalloc(sizeof(*pl), GFP_KERNEL);
221                 if (!pl)
222                         return -ENOMEM;
223                 pl_was_allocated = true;
224                 pl->prog = prog;
225                 list_add_tail(&pl->node, progs);
226         } else {
227                 if (list_empty(progs)) {
228                         pl = kmalloc(sizeof(*pl), GFP_KERNEL);
229                         if (!pl)
230                                 return -ENOMEM;
231                         pl_was_allocated = true;
232                         list_add_tail(&pl->node, progs);
233                 } else {
234                         pl = list_first_entry(progs, typeof(*pl), node);
235                         old_prog = pl->prog;
236                         pl_was_allocated = false;
237                 }
238                 pl->prog = prog;
239         }
240 
241         cgrp->bpf.flags[type] = flags;
242 
243         /* allocate and recompute effective prog arrays */
244         css_for_each_descendant_pre(css, &cgrp->self) {
245                 struct cgroup *desc = container_of(css, struct cgroup, self);
246 
247                 err = compute_effective_progs(desc, type, &desc->bpf.inactive);
248                 if (err)
249                         goto cleanup;
250         }
251 
252         /* all allocations were successful. Activate all prog arrays */
253         css_for_each_descendant_pre(css, &cgrp->self) {
254                 struct cgroup *desc = container_of(css, struct cgroup, self);
255 
256                 activate_effective_progs(desc, type, desc->bpf.inactive);
257                 desc->bpf.inactive = NULL;
258         }
259 
260         static_branch_inc(&cgroup_bpf_enabled_key);
261         if (old_prog) {
262                 bpf_prog_put(old_prog);
263                 static_branch_dec(&cgroup_bpf_enabled_key);
264         }
265         return 0;
266 
267 cleanup:
268         /* oom while computing effective. Free all computed effective arrays
269          * since they were not activated
270          */
271         css_for_each_descendant_pre(css, &cgrp->self) {
272                 struct cgroup *desc = container_of(css, struct cgroup, self);
273 
274                 bpf_prog_array_free(desc->bpf.inactive);
275                 desc->bpf.inactive = NULL;
276         }
277 
278         /* and cleanup the prog list */
279         pl->prog = old_prog;
280         if (pl_was_allocated) {
281                 list_del(&pl->node);
282                 kfree(pl);
283         }
284         return err;
285 }
286 
287 /**
288  * __cgroup_bpf_detach() - Detach the program from a cgroup, and
289  *                         propagate the change to descendants
290  * @cgrp: The cgroup which descendants to traverse
291  * @prog: A program to detach or NULL
292  * @type: Type of detach operation
293  *
294  * Must be called with cgroup_mutex held.
295  */
296 int __cgroup_bpf_detach(struct cgroup *cgrp, struct bpf_prog *prog,
297                         enum bpf_attach_type type, u32 unused_flags)
298 {
299         struct list_head *progs = &cgrp->bpf.progs[type];
300         u32 flags = cgrp->bpf.flags[type];
301         struct bpf_prog *old_prog = NULL;
302         struct cgroup_subsys_state *css;
303         struct bpf_prog_list *pl;
304         int err;
305 
306         if (flags & BPF_F_ALLOW_MULTI) {
307                 if (!prog)
308                         /* to detach MULTI prog the user has to specify valid FD
309                          * of the program to be detached
310                          */
311                         return -EINVAL;
312         } else {
313                 if (list_empty(progs))
314                         /* report error when trying to detach and nothing is attached */
315                         return -ENOENT;
316         }
317 
318         if (flags & BPF_F_ALLOW_MULTI) {
319                 /* find the prog and detach it */
320                 list_for_each_entry(pl, progs, node) {
321                         if (pl->prog != prog)
322                                 continue;
323                         old_prog = prog;
324                         /* mark it deleted, so it's ignored while
325                          * recomputing effective
326                          */
327                         pl->prog = NULL;
328                         break;
329                 }
330                 if (!old_prog)
331                         return -ENOENT;
332         } else {
333                 /* to maintain backward compatibility NONE and OVERRIDE cgroups
334                  * allow detaching with invalid FD (prog==NULL)
335                  */
336                 pl = list_first_entry(progs, typeof(*pl), node);
337                 old_prog = pl->prog;
338                 pl->prog = NULL;
339         }
340 
341         /* allocate and recompute effective prog arrays */
342         css_for_each_descendant_pre(css, &cgrp->self) {
343                 struct cgroup *desc = container_of(css, struct cgroup, self);
344 
345                 err = compute_effective_progs(desc, type, &desc->bpf.inactive);
346                 if (err)
347                         goto cleanup;
348         }
349 
350         /* all allocations were successful. Activate all prog arrays */
351         css_for_each_descendant_pre(css, &cgrp->self) {
352                 struct cgroup *desc = container_of(css, struct cgroup, self);
353 
354                 activate_effective_progs(desc, type, desc->bpf.inactive);
355                 desc->bpf.inactive = NULL;
356         }
357 
358         /* now can actually delete it from this cgroup list */
359         list_del(&pl->node);
360         kfree(pl);
361         if (list_empty(progs))
362                 /* last program was detached, reset flags to zero */
363                 cgrp->bpf.flags[type] = 0;
364 
365         bpf_prog_put(old_prog);
366         static_branch_dec(&cgroup_bpf_enabled_key);
367         return 0;
368 
369 cleanup:
370         /* oom while computing effective. Free all computed effective arrays
371          * since they were not activated
372          */
373         css_for_each_descendant_pre(css, &cgrp->self) {
374                 struct cgroup *desc = container_of(css, struct cgroup, self);
375 
376                 bpf_prog_array_free(desc->bpf.inactive);
377                 desc->bpf.inactive = NULL;
378         }
379 
380         /* and restore back old_prog */
381         pl->prog = old_prog;
382         return err;
383 }
384 
385 /* Must be called with cgroup_mutex held to avoid races. */
386 int __cgroup_bpf_query(struct cgroup *cgrp, const union bpf_attr *attr,
387                        union bpf_attr __user *uattr)
388 {
389         __u32 __user *prog_ids = u64_to_user_ptr(attr->query.prog_ids);
390         enum bpf_attach_type type = attr->query.attach_type;
391         struct list_head *progs = &cgrp->bpf.progs[type];
392         u32 flags = cgrp->bpf.flags[type];
393         int cnt, ret = 0, i;
394 
395         if (attr->query.query_flags & BPF_F_QUERY_EFFECTIVE)
396                 cnt = bpf_prog_array_length(cgrp->bpf.effective[type]);
397         else
398                 cnt = prog_list_length(progs);
399 
400         if (copy_to_user(&uattr->query.attach_flags, &flags, sizeof(flags)))
401                 return -EFAULT;
402         if (copy_to_user(&uattr->query.prog_cnt, &cnt, sizeof(cnt)))
403                 return -EFAULT;
404         if (attr->query.prog_cnt == 0 || !prog_ids || !cnt)
405                 /* return early if user requested only program count + flags */
406                 return 0;
407         if (attr->query.prog_cnt < cnt) {
408                 cnt = attr->query.prog_cnt;
409                 ret = -ENOSPC;
410         }
411 
412         if (attr->query.query_flags & BPF_F_QUERY_EFFECTIVE) {
413                 return bpf_prog_array_copy_to_user(cgrp->bpf.effective[type],
414                                                    prog_ids, cnt);
415         } else {
416                 struct bpf_prog_list *pl;
417                 u32 id;
418 
419                 i = 0;
420                 list_for_each_entry(pl, progs, node) {
421                         id = pl->prog->aux->id;
422                         if (copy_to_user(prog_ids + i, &id, sizeof(id)))
423                                 return -EFAULT;
424                         if (++i == cnt)
425                                 break;
426                 }
427         }
428         return ret;
429 }
430 
431 /**
432  * __cgroup_bpf_run_filter_skb() - Run a program for packet filtering
433  * @sk: The socket sending or receiving traffic
434  * @skb: The skb that is being sent or received
435  * @type: The type of program to be exectuted
436  *
437  * If no socket is passed, or the socket is not of type INET or INET6,
438  * this function does nothing and returns 0.
439  *
440  * The program type passed in via @type must be suitable for network
441  * filtering. No further check is performed to assert that.
442  *
443  * This function will return %-EPERM if any if an attached program was found
444  * and if it returned != 1 during execution. In all other cases, 0 is returned.
445  */
446 int __cgroup_bpf_run_filter_skb(struct sock *sk,
447                                 struct sk_buff *skb,
448                                 enum bpf_attach_type type)
449 {
450         unsigned int offset = skb->data - skb_network_header(skb);
451         struct sock *save_sk;
452         struct cgroup *cgrp;
453         int ret;
454 
455         if (!sk || !sk_fullsock(sk))
456                 return 0;
457 
458         if (sk->sk_family != AF_INET && sk->sk_family != AF_INET6)
459                 return 0;
460 
461         cgrp = sock_cgroup_ptr(&sk->sk_cgrp_data);
462         save_sk = skb->sk;
463         skb->sk = sk;
464         __skb_push(skb, offset);
465         ret = BPF_PROG_RUN_ARRAY(cgrp->bpf.effective[type], skb,
466                                  bpf_prog_run_save_cb);
467         __skb_pull(skb, offset);
468         skb->sk = save_sk;
469         return ret == 1 ? 0 : -EPERM;
470 }
471 EXPORT_SYMBOL(__cgroup_bpf_run_filter_skb);
472 
473 /**
474  * __cgroup_bpf_run_filter_sk() - Run a program on a sock
475  * @sk: sock structure to manipulate
476  * @type: The type of program to be exectuted
477  *
478  * socket is passed is expected to be of type INET or INET6.
479  *
480  * The program type passed in via @type must be suitable for sock
481  * filtering. No further check is performed to assert that.
482  *
483  * This function will return %-EPERM if any if an attached program was found
484  * and if it returned != 1 during execution. In all other cases, 0 is returned.
485  */
486 int __cgroup_bpf_run_filter_sk(struct sock *sk,
487                                enum bpf_attach_type type)
488 {
489         struct cgroup *cgrp = sock_cgroup_ptr(&sk->sk_cgrp_data);
490         int ret;
491 
492         ret = BPF_PROG_RUN_ARRAY(cgrp->bpf.effective[type], sk, BPF_PROG_RUN);
493         return ret == 1 ? 0 : -EPERM;
494 }
495 EXPORT_SYMBOL(__cgroup_bpf_run_filter_sk);
496 
497 /**
498  * __cgroup_bpf_run_filter_sock_addr() - Run a program on a sock and
499  *                                       provided by user sockaddr
500  * @sk: sock struct that will use sockaddr
501  * @uaddr: sockaddr struct provided by user
502  * @type: The type of program to be exectuted
503  *
504  * socket is expected to be of type INET or INET6.
505  *
506  * This function will return %-EPERM if an attached program is found and
507  * returned value != 1 during execution. In all other cases, 0 is returned.
508  */
509 int __cgroup_bpf_run_filter_sock_addr(struct sock *sk,
510                                       struct sockaddr *uaddr,
511                                       enum bpf_attach_type type)
512 {
513         struct bpf_sock_addr_kern ctx = {
514                 .sk = sk,
515                 .uaddr = uaddr,
516         };
517         struct cgroup *cgrp;
518         int ret;
519 
520         /* Check socket family since not all sockets represent network
521          * endpoint (e.g. AF_UNIX).
522          */
523         if (sk->sk_family != AF_INET && sk->sk_family != AF_INET6)
524                 return 0;
525 
526         cgrp = sock_cgroup_ptr(&sk->sk_cgrp_data);
527         ret = BPF_PROG_RUN_ARRAY(cgrp->bpf.effective[type], &ctx, BPF_PROG_RUN);
528 
529         return ret == 1 ? 0 : -EPERM;
530 }
531 EXPORT_SYMBOL(__cgroup_bpf_run_filter_sock_addr);
532 
533 /**
534  * __cgroup_bpf_run_filter_sock_ops() - Run a program on a sock
535  * @sk: socket to get cgroup from
536  * @sock_ops: bpf_sock_ops_kern struct to pass to program. Contains
537  * sk with connection information (IP addresses, etc.) May not contain
538  * cgroup info if it is a req sock.
539  * @type: The type of program to be exectuted
540  *
541  * socket passed is expected to be of type INET or INET6.
542  *
543  * The program type passed in via @type must be suitable for sock_ops
544  * filtering. No further check is performed to assert that.
545  *
546  * This function will return %-EPERM if any if an attached program was found
547  * and if it returned != 1 during execution. In all other cases, 0 is returned.
548  */
549 int __cgroup_bpf_run_filter_sock_ops(struct sock *sk,
550                                      struct bpf_sock_ops_kern *sock_ops,
551                                      enum bpf_attach_type type)
552 {
553         struct cgroup *cgrp = sock_cgroup_ptr(&sk->sk_cgrp_data);
554         int ret;
555 
556         ret = BPF_PROG_RUN_ARRAY(cgrp->bpf.effective[type], sock_ops,
557                                  BPF_PROG_RUN);
558         return ret == 1 ? 0 : -EPERM;
559 }
560 EXPORT_SYMBOL(__cgroup_bpf_run_filter_sock_ops);
561 
562 int __cgroup_bpf_check_dev_permission(short dev_type, u32 major, u32 minor,
563                                       short access, enum bpf_attach_type type)
564 {
565         struct cgroup *cgrp;
566         struct bpf_cgroup_dev_ctx ctx = {
567                 .access_type = (access << 16) | dev_type,
568                 .major = major,
569                 .minor = minor,
570         };
571         int allow = 1;
572 
573         rcu_read_lock();
574         cgrp = task_dfl_cgroup(current);
575         allow = BPF_PROG_RUN_ARRAY(cgrp->bpf.effective[type], &ctx,
576                                    BPF_PROG_RUN);
577         rcu_read_unlock();
578 
579         return !allow;
580 }
581 EXPORT_SYMBOL(__cgroup_bpf_check_dev_permission);
582 
583 static const struct bpf_func_proto *
584 cgroup_dev_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
585 {
586         switch (func_id) {
587         case BPF_FUNC_map_lookup_elem:
588                 return &bpf_map_lookup_elem_proto;
589         case BPF_FUNC_map_update_elem:
590                 return &bpf_map_update_elem_proto;
591         case BPF_FUNC_map_delete_elem:
592                 return &bpf_map_delete_elem_proto;
593         case BPF_FUNC_get_current_uid_gid:
594                 return &bpf_get_current_uid_gid_proto;
595         case BPF_FUNC_trace_printk:
596                 if (capable(CAP_SYS_ADMIN))
597                         return bpf_get_trace_printk_proto();
598         default:
599                 return NULL;
600         }
601 }
602 
603 static bool cgroup_dev_is_valid_access(int off, int size,
604                                        enum bpf_access_type type,
605                                        const struct bpf_prog *prog,
606                                        struct bpf_insn_access_aux *info)
607 {
608         const int size_default = sizeof(__u32);
609 
610         if (type == BPF_WRITE)
611                 return false;
612 
613         if (off < 0 || off + size > sizeof(struct bpf_cgroup_dev_ctx))
614                 return false;
615         /* The verifier guarantees that size > 0. */
616         if (off % size != 0)
617                 return false;
618 
619         switch (off) {
620         case bpf_ctx_range(struct bpf_cgroup_dev_ctx, access_type):
621                 bpf_ctx_record_field_size(info, size_default);
622                 if (!bpf_ctx_narrow_access_ok(off, size, size_default))
623                         return false;
624                 break;
625         default:
626                 if (size != size_default)
627                         return false;
628         }
629 
630         return true;
631 }
632 
633 const struct bpf_prog_ops cg_dev_prog_ops = {
634 };
635 
636 const struct bpf_verifier_ops cg_dev_verifier_ops = {
637         .get_func_proto         = cgroup_dev_func_proto,
638         .is_valid_access        = cgroup_dev_is_valid_access,
639 };
640 

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