net/unix/garbage.c

   1 // SPDX-License-Identifier: GPL-2.0-or-later
   2 /*
   3  * NET3:        Garbage Collector For AF_UNIX sockets
   4  *
   5  * Garbage Collector:
   6  *      Copyright (C) Barak A. Pearlmutter.
   7  *
   8  * Chopped about by Alan Cox 22/3/96 to make it fit the AF_UNIX socket problem.
   9  * If it doesn't work blame me, it worked when Barak sent it.
  10  *
  11  * Assumptions:
  12  *
  13  *  - object w/ a bit
  14  *  - free list
  15  *
  16  * Current optimizations:
  17  *
  18  *  - explicit stack instead of recursion
  19  *  - tail recurse on first born instead of immediate push/pop
  20  *  - we gather the stuff that should not be killed into tree
  21  *    and stack is just a path from root to the current pointer.
  22  *
  23  *  Future optimizations:
  24  *
  25  *  - don't just push entire root set; process in place
  26  *
  27  *  Fixes:
  28  *      Alan Cox        07 Sept 1997    Vmalloc internal stack as needed.
  29  *                                      Cope with changing max_files.
  30  *      Al Viro         11 Oct 1998
  31  *              Graph may have cycles. That is, we can send the descriptor
  32  *              of foo to bar and vice versa. Current code chokes on that.
  33  *              Fix: move SCM_RIGHTS ones into the separate list and then
  34  *              skb_free() them all instead of doing explicit fput's.
  35  *              Another problem: since fput() may block somebody may
  36  *              create a new unix_socket when we are in the middle of sweep
  37  *              phase. Fix: revert the logic wrt MARKED. Mark everything
  38  *              upon the beginning and unmark non-junk ones.
  39  *
  40  *              [12 Oct 1998] AAARGH! New code purges all SCM_RIGHTS
  41  *              sent to connect()'ed but still not accept()'ed sockets.
  42  *              Fixed. Old code had slightly different problem here:
  43  *              extra fput() in situation when we passed the descriptor via
  44  *              such socket and closed it (descriptor). That would happen on
  45  *              each unix_gc() until the accept(). Since the struct file in
  46  *              question would go to the free list and might be reused...
  47  *              That might be the reason of random oopses on filp_close()
  48  *              in unrelated processes.
  49  *
  50  *      AV              28 Feb 1999
  51  *              Kill the explicit allocation of stack. Now we keep the tree
  52  *              with root in dummy + pointer (gc_current) to one of the nodes.
  53  *              Stack is represented as path from gc_current to dummy. Unmark
  54  *              now means "add to tree". Push == "make it a son of gc_current".
  55  *              Pop == "move gc_current to parent". We keep only pointers to
  56  *              parents (->gc_tree).
  57  *      AV              1 Mar 1999
  58  *              Damn. Added missing check for ->dead in listen queues scanning.
  59  *
  60  *      Miklos Szeredi 25 Jun 2007
  61  *              Reimplement with a cycle collecting algorithm. This should
  62  *              solve several problems with the previous code, like being racy
  63  *              wrt receive and holding up unrelated socket operations.
  64  */
  65
  66 #include <linux/kernel.h>
  67 #include <linux/string.h>
  68 #include <linux/socket.h>
  69 #include <linux/un.h>
  70 #include <linux/net.h>
  71 #include <linux/fs.h>
  72 #include <linux/skbuff.h>
  73 #include <linux/netdevice.h>
  74 #include <linux/file.h>
  75 #include <linux/proc_fs.h>
  76 #include <linux/mutex.h>
  77 #include <linux/wait.h>
  78
  79 #include <net/sock.h>
  80 #include <net/af_unix.h>
  81 #include <net/scm.h>
  82 #include <net/tcp_states.h>
  83
  84 struct unix_sock *unix_get_socket(struct file *filp)
  85 {
  86         struct inode *inode = file_inode(filp);
  87
  88         /* Socket ? */
  89         if (S_ISSOCK(inode->i_mode) && !(filp->f_mode & FMODE_PATH)) {
  90                 struct socket *sock = SOCKET_I(inode);
  91                 const struct proto_ops *ops;
  92                 struct sock *sk = sock->sk;
  93
  94                 ops = READ_ONCE(sock->ops);
  95
  96                 /* PF_UNIX ? */
  97                 if (sk && ops && ops->family == PF_UNIX)
  98                         return unix_sk(sk);
  99         }
 100
 101         return NULL;
 102 }
 103
 104 static struct unix_vertex *unix_edge_successor(struct unix_edge *edge)
 105 {
 106         /* If an embryo socket has a fd,
 107          * the listener indirectly holds the fd's refcnt.
 108          */
 109         if (edge->successor->listener)
 110                 return unix_sk(edge->successor->listener)->vertex;
 111
 112         return edge->successor->vertex;
 113 }
 114
 115 static bool unix_graph_maybe_cyclic;
 116 static bool unix_graph_grouped;
 117
 118 static void unix_update_graph(struct unix_vertex *vertex)
 119 {
 120         /* If the receiver socket is not inflight, no cyclic
 121          * reference could be formed.
 122          */
 123         if (!vertex)
 124                 return;
 125
 126         unix_graph_maybe_cyclic = true;
 127         unix_graph_grouped = false;
 128 }
 129
 130 static LIST_HEAD(unix_unvisited_vertices);
 131
 132 enum unix_vertex_index {
 133         UNIX_VERTEX_INDEX_MARK1,
 134         UNIX_VERTEX_INDEX_MARK2,
 135         UNIX_VERTEX_INDEX_START,
 136 };
 137
 138 static unsigned long unix_vertex_unvisited_index = UNIX_VERTEX_INDEX_MARK1;
 139
 140 static void unix_add_edge(struct scm_fp_list *fpl, struct unix_edge *edge)
 141 {
 142         struct unix_vertex *vertex = edge->predecessor->vertex;
 143
 144         if (!vertex) {
 145                 vertex = list_first_entry(&fpl->vertices, typeof(*vertex), entry);
 146                 vertex->index = unix_vertex_unvisited_index;
 147                 vertex->out_degree = 0;
 148                 INIT_LIST_HEAD(&vertex->edges);
 149                 INIT_LIST_HEAD(&vertex->scc_entry);
 150
 151                 list_move_tail(&vertex->entry, &unix_unvisited_vertices);
 152                 edge->predecessor->vertex = vertex;
 153         }
 154
 155         vertex->out_degree++;
 156         list_add_tail(&edge->vertex_entry, &vertex->edges);
 157
 158         unix_update_graph(unix_edge_successor(edge));
 159 }
 160
 161 static void unix_del_edge(struct scm_fp_list *fpl, struct unix_edge *edge)
 162 {
 163         struct unix_vertex *vertex = edge->predecessor->vertex;
 164
 165         if (!fpl->dead)
 166                 unix_update_graph(unix_edge_successor(edge));
 167
 168         list_del(&edge->vertex_entry);
 169         vertex->out_degree--;
 170
 171         if (!vertex->out_degree) {
 172                 edge->predecessor->vertex = NULL;
 173                 list_move_tail(&vertex->entry, &fpl->vertices);
 174         }
 175 }
 176
 177 static void unix_free_vertices(struct scm_fp_list *fpl)
 178 {
 179         struct unix_vertex *vertex, *next_vertex;
 180
 181         list_for_each_entry_safe(vertex, next_vertex, &fpl->vertices, entry) {
 182                 list_del(&vertex->entry);
 183                 kfree(vertex);
 184         }
 185 }
 186
 187 static DEFINE_SPINLOCK(unix_gc_lock);
 188 unsigned int unix_tot_inflight;
 189
 190 void unix_add_edges(struct scm_fp_list *fpl, struct unix_sock *receiver)
 191 {
 192         int i = 0, j = 0;
 193
 194         spin_lock(&unix_gc_lock);
 195
 196         if (!fpl->count_unix)
 197                 goto out;
 198
 199         do {
 200                 struct unix_sock *inflight = unix_get_socket(fpl->fp[j++]);
 201                 struct unix_edge *edge;
 202
 203                 if (!inflight)
 204                         continue;
 205
 206                 edge = fpl->edges + i++;
 207                 edge->predecessor = inflight;
 208                 edge->successor = receiver;
 209
 210                 unix_add_edge(fpl, edge);
 211         } while (i < fpl->count_unix);
 212
 213         receiver->scm_stat.nr_unix_fds += fpl->count_unix;
 214         WRITE_ONCE(unix_tot_inflight, unix_tot_inflight + fpl->count_unix);
 215 out:
 216         WRITE_ONCE(fpl->user->unix_inflight, fpl->user->unix_inflight + fpl->count);
 217
 218         spin_unlock(&unix_gc_lock);
 219
 220         fpl->inflight = true;
 221
 222         unix_free_vertices(fpl);
 223 }
 224
 225 void unix_del_edges(struct scm_fp_list *fpl)
 226 {
 227         struct unix_sock *receiver;
 228         int i = 0;
 229
 230         spin_lock(&unix_gc_lock);
 231
 232         if (!fpl->count_unix)
 233                 goto out;
 234
 235         do {
 236                 struct unix_edge *edge = fpl->edges + i++;
 237
 238                 unix_del_edge(fpl, edge);
 239         } while (i < fpl->count_unix);
 240
 241         if (!fpl->dead) {
 242                 receiver = fpl->edges[0].successor;
 243                 receiver->scm_stat.nr_unix_fds -= fpl->count_unix;
 244         }
 245         WRITE_ONCE(unix_tot_inflight, unix_tot_inflight - fpl->count_unix);
 246 out:
 247         WRITE_ONCE(fpl->user->unix_inflight, fpl->user->unix_inflight - fpl->count);
 248
 249         spin_unlock(&unix_gc_lock);
 250
 251         fpl->inflight = false;
 252 }
 253
 254 void unix_update_edges(struct unix_sock *receiver)
 255 {
 256         /* nr_unix_fds is only updated under unix_state_lock().
 257          * If it's 0 here, the embryo socket is not part of the
 258          * inflight graph, and GC will not see it, so no lock needed.
 259          */
 260         if (!receiver->scm_stat.nr_unix_fds) {
 261                 receiver->listener = NULL;
 262         } else {
 263                 spin_lock(&unix_gc_lock);
 264                 unix_update_graph(unix_sk(receiver->listener)->vertex);
 265                 receiver->listener = NULL;
 266                 spin_unlock(&unix_gc_lock);
 267         }
 268 }
 269
 270 int unix_prepare_fpl(struct scm_fp_list *fpl)
 271 {
 272         struct unix_vertex *vertex;
 273         int i;
 274
 275         if (!fpl->count_unix)
 276                 return 0;
 277
 278         for (i = 0; i < fpl->count_unix; i++) {
 279                 vertex = kmalloc(sizeof(*vertex), GFP_KERNEL);
 280                 if (!vertex)
 281                         goto err;
 282
 283                 list_add(&vertex->entry, &fpl->vertices);
 284         }
 285
 286         fpl->edges = kvmalloc_array(fpl->count_unix, sizeof(*fpl->edges),
 287                                     GFP_KERNEL_ACCOUNT);
 288         if (!fpl->edges)
 289                 goto err;
 290
 291         return 0;
 292
 293 err:
 294         unix_free_vertices(fpl);
 295         return -ENOMEM;
 296 }
 297
 298 void unix_destroy_fpl(struct scm_fp_list *fpl)
 299 {
 300         if (fpl->inflight)
 301                 unix_del_edges(fpl);
 302
 303         kvfree(fpl->edges);
 304         unix_free_vertices(fpl);
 305 }
 306
 307 static bool unix_vertex_dead(struct unix_vertex *vertex)
 308 {
 309         struct unix_edge *edge;
 310         struct unix_sock *u;
 311         long total_ref;
 312
 313         list_for_each_entry(edge, &vertex->edges, vertex_entry) {
 314                 struct unix_vertex *next_vertex = unix_edge_successor(edge);
 315
 316                 /* The vertex's fd can be received by a non-inflight socket. */
 317                 if (!next_vertex)
 318                         return false;
 319
 320                 /* The vertex's fd can be received by an inflight socket in
 321                  * another SCC.
 322                  */
 323                 if (next_vertex->scc_index != vertex->scc_index)
 324                         return false;
 325         }
 326
 327         /* No receiver exists out of the same SCC. */
 328
 329         edge = list_first_entry(&vertex->edges, typeof(*edge), vertex_entry);
 330         u = edge->predecessor;
 331         total_ref = file_count(u->sk.sk_socket->file);
 332
 333         /* If not close()d, total_ref > out_degree. */
 334         if (total_ref != vertex->out_degree)
 335                 return false;
 336
 337         return true;
 338 }
 339
 340 static void unix_collect_queue(struct unix_sock *u, struct sk_buff_head *hitlist)
 341 {
 342         skb_queue_splice_init(&u->sk.sk_receive_queue, hitlist);
 343
 344 #if IS_ENABLED(CONFIG_AF_UNIX_OOB)
 345         if (u->oob_skb) {
 346                 WARN_ON_ONCE(skb_unref(u->oob_skb));
 347                 u->oob_skb = NULL;
 348         }
 349 #endif
 350 }
 351
 352 static void unix_collect_skb(struct list_head *scc, struct sk_buff_head *hitlist)
 353 {
 354         struct unix_vertex *vertex;
 355
 356         list_for_each_entry_reverse(vertex, scc, scc_entry) {
 357                 struct sk_buff_head *queue;
 358                 struct unix_edge *edge;
 359                 struct unix_sock *u;
 360
 361                 edge = list_first_entry(&vertex->edges, typeof(*edge), vertex_entry);
 362                 u = edge->predecessor;
 363                 queue = &u->sk.sk_receive_queue;
 364
 365                 spin_lock(&queue->lock);
 366
 367                 if (u->sk.sk_state == TCP_LISTEN) {
 368                         struct sk_buff *skb;
 369
 370                         skb_queue_walk(queue, skb) {
 371                                 struct sk_buff_head *embryo_queue = &skb->sk->sk_receive_queue;
 372
 373                                 spin_lock(&embryo_queue->lock);
 374                                 unix_collect_queue(unix_sk(skb->sk), hitlist);
 375                                 spin_unlock(&embryo_queue->lock);
 376                         }
 377                 } else {
 378                         unix_collect_queue(u, hitlist);
 379                 }
 380
 381                 spin_unlock(&queue->lock);
 382         }
 383 }
 384
 385 static bool unix_scc_cyclic(struct list_head *scc)
 386 {
 387         struct unix_vertex *vertex;
 388         struct unix_edge *edge;
 389
 390         /* SCC containing multiple vertices ? */
 391         if (!list_is_singular(scc))
 392                 return true;
 393
 394         vertex = list_first_entry(scc, typeof(*vertex), scc_entry);
 395
 396         /* Self-reference or a embryo-listener circle ? */
 397         list_for_each_entry(edge, &vertex->edges, vertex_entry) {
 398                 if (unix_edge_successor(edge) == vertex)
 399                         return true;
 400         }
 401
 402         return false;
 403 }
 404
 405 static LIST_HEAD(unix_visited_vertices);
 406 static unsigned long unix_vertex_grouped_index = UNIX_VERTEX_INDEX_MARK2;
 407
 408 static void __unix_walk_scc(struct unix_vertex *vertex, unsigned long *last_index,
 409                             struct sk_buff_head *hitlist)
 410 {
 411         LIST_HEAD(vertex_stack);
 412         struct unix_edge *edge;
 413         LIST_HEAD(edge_stack);
 414
 415 next_vertex:
 416         /* Push vertex to vertex_stack and mark it as on-stack
 417          * (index >= UNIX_VERTEX_INDEX_START).
 418          * The vertex will be popped when finalising SCC later.
 419          */
 420         list_add(&vertex->scc_entry, &vertex_stack);
 421
 422         vertex->index = *last_index;
 423         vertex->scc_index = *last_index;
 424         (*last_index)++;
 425
 426         /* Explore neighbour vertices (receivers of the current vertex's fd). */
 427         list_for_each_entry(edge, &vertex->edges, vertex_entry) {
 428                 struct unix_vertex *next_vertex = unix_edge_successor(edge);
 429
 430                 if (!next_vertex)
 431                         continue;
 432
 433                 if (next_vertex->index == unix_vertex_unvisited_index) {
 434                         /* Iterative deepening depth first search
 435                          *
 436                          *   1. Push a forward edge to edge_stack and set
 437                          *      the successor to vertex for the next iteration.
 438                          */
 439                         list_add(&edge->stack_entry, &edge_stack);
 440
 441                         vertex = next_vertex;
 442                         goto next_vertex;
 443
 444                         /*   2. Pop the edge directed to the current vertex
 445                          *      and restore the ancestor for backtracking.
 446                          */
 447 prev_vertex:
 448                         edge = list_first_entry(&edge_stack, typeof(*edge), stack_entry);
 449                         list_del_init(&edge->stack_entry);
 450
 451                         next_vertex = vertex;
 452                         vertex = edge->predecessor->vertex;
 453
 454                         /* If the successor has a smaller scc_index, two vertices
 455                          * are in the same SCC, so propagate the smaller scc_index
 456                          * to skip SCC finalisation.
 457                          */
 458                         vertex->scc_index = min(vertex->scc_index, next_vertex->scc_index);
 459                 } else if (next_vertex->index != unix_vertex_grouped_index) {
 460                         /* Loop detected by a back/cross edge.
 461                          *
 462                          * The successor is on vertex_stack, so two vertices are in
 463                          * the same SCC.  If the successor has a smaller *scc_index*,
 464                          * propagate it to skip SCC finalisation.
 465                          */
 466                         vertex->scc_index = min(vertex->scc_index, next_vertex->scc_index);
 467                 } else {
 468                         /* The successor was already grouped as another SCC */
 469                 }
 470         }
 471
 472         if (vertex->index == vertex->scc_index) {
 473                 struct unix_vertex *v;
 474                 struct list_head scc;
 475                 bool scc_dead = true;
 476
 477                 /* SCC finalised.
 478                  *
 479                  * If the scc_index was not updated, all the vertices above on
 480                  * vertex_stack are in the same SCC.  Group them using scc_entry.
 481                  */
 482                 __list_cut_position(&scc, &vertex_stack, &vertex->scc_entry);
 483
 484                 list_for_each_entry_reverse(v, &scc, scc_entry) {
 485                         /* Don't restart DFS from this vertex in unix_walk_scc(). */
 486                         list_move_tail(&v->entry, &unix_visited_vertices);
 487
 488                         /* Mark vertex as off-stack. */
 489                         v->index = unix_vertex_grouped_index;
 490
 491                         if (scc_dead)
 492                                 scc_dead = unix_vertex_dead(v);
 493                 }
 494
 495                 if (scc_dead)
 496                         unix_collect_skb(&scc, hitlist);
 497                 else if (!unix_graph_maybe_cyclic)
 498                         unix_graph_maybe_cyclic = unix_scc_cyclic(&scc);
 499
 500                 list_del(&scc);
 501         }
 502
 503         /* Need backtracking ? */
 504         if (!list_empty(&edge_stack))
 505                 goto prev_vertex;
 506 }
 507
 508 static void unix_walk_scc(struct sk_buff_head *hitlist)
 509 {
 510         unsigned long last_index = UNIX_VERTEX_INDEX_START;
 511
 512         unix_graph_maybe_cyclic = false;
 513
 514         /* Visit every vertex exactly once.
 515          * __unix_walk_scc() moves visited vertices to unix_visited_vertices.
 516          */
 517         while (!list_empty(&unix_unvisited_vertices)) {
 518                 struct unix_vertex *vertex;
 519
 520                 vertex = list_first_entry(&unix_unvisited_vertices, typeof(*vertex), entry);
 521                 __unix_walk_scc(vertex, &last_index, hitlist);
 522         }
 523
 524         list_replace_init(&unix_visited_vertices, &unix_unvisited_vertices);
 525         swap(unix_vertex_unvisited_index, unix_vertex_grouped_index);
 526
 527         unix_graph_grouped = true;
 528 }
 529
 530 static void unix_walk_scc_fast(struct sk_buff_head *hitlist)
 531 {
 532         unix_graph_maybe_cyclic = false;
 533
 534         while (!list_empty(&unix_unvisited_vertices)) {
 535                 struct unix_vertex *vertex;
 536                 struct list_head scc;
 537                 bool scc_dead = true;
 538
 539                 vertex = list_first_entry(&unix_unvisited_vertices, typeof(*vertex), entry);
 540                 list_add(&scc, &vertex->scc_entry);
 541
 542                 list_for_each_entry_reverse(vertex, &scc, scc_entry) {
 543                         list_move_tail(&vertex->entry, &unix_visited_vertices);
 544
 545                         if (scc_dead)
 546                                 scc_dead = unix_vertex_dead(vertex);
 547                 }
 548
 549                 if (scc_dead)
 550                         unix_collect_skb(&scc, hitlist);
 551                 else if (!unix_graph_maybe_cyclic)
 552                         unix_graph_maybe_cyclic = unix_scc_cyclic(&scc);
 553
 554                 list_del(&scc);
 555         }
 556
 557         list_replace_init(&unix_visited_vertices, &unix_unvisited_vertices);
 558 }
 559
 560 static bool gc_in_progress;
 561
 562 static void __unix_gc(struct work_struct *work)
 563 {
 564         struct sk_buff_head hitlist;
 565         struct sk_buff *skb;
 566
 567         spin_lock(&unix_gc_lock);
 568
 569         if (!unix_graph_maybe_cyclic) {
 570                 spin_unlock(&unix_gc_lock);
 571                 goto skip_gc;
 572         }
 573
 574         __skb_queue_head_init(&hitlist);
 575
 576         if (unix_graph_grouped)
 577                 unix_walk_scc_fast(&hitlist);
 578         else
 579                 unix_walk_scc(&hitlist);
 580
 581         spin_unlock(&unix_gc_lock);
 582
 583         skb_queue_walk(&hitlist, skb) {
 584                 if (UNIXCB(skb).fp)
 585                         UNIXCB(skb).fp->dead = true;
 586         }
 587
 588         __skb_queue_purge(&hitlist);
 589 skip_gc:
 590         WRITE_ONCE(gc_in_progress, false);
 591 }
 592
 593 static DECLARE_WORK(unix_gc_work, __unix_gc);
 594
 595 void unix_gc(void)
 596 {
 597         WRITE_ONCE(gc_in_progress, true);
 598         queue_work(system_unbound_wq, &unix_gc_work);
 599 }
 600
 601 #define UNIX_INFLIGHT_TRIGGER_GC 16000
 602 #define UNIX_INFLIGHT_SANE_USER (SCM_MAX_FD * 8)
 603
 604 void wait_for_unix_gc(struct scm_fp_list *fpl)
 605 {
 606         /* If number of inflight sockets is insane,
 607          * force a garbage collect right now.
 608          *
 609          * Paired with the WRITE_ONCE() in unix_inflight(),
 610          * unix_notinflight(), and __unix_gc().
 611          */
 612         if (READ_ONCE(unix_tot_inflight) > UNIX_INFLIGHT_TRIGGER_GC &&
 613             !READ_ONCE(gc_in_progress))
 614                 unix_gc();
 615
 616         /* Penalise users who want to send AF_UNIX sockets
 617          * but whose sockets have not been received yet.
 618          */
 619         if (!fpl || !fpl->count_unix ||
 620             READ_ONCE(fpl->user->unix_inflight) < UNIX_INFLIGHT_SANE_USER)
 621                 return;
 622
 623         if (READ_ONCE(gc_in_progress))
 624                 flush_work(&unix_gc_work);
 625 }