net/unix/garbage.c

   1 /*
   2  * NET3:        Garbage Collector For AF_UNIX sockets
   3  *
   4  * Garbage Collector:
   5  *      Copyright (C) Barak A. Pearlmutter.
   6  *      Released under the GPL version 2 or later.
   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  *      This program is free software; you can redistribute it and/or
  28  *      modify it under the terms of the GNU General Public License
  29  *      as published by the Free Software Foundation; either version
  30  *      2 of the License, or (at your option) any later version.
  31  *
  32  *  Fixes:
  33  *      Alan Cox        07 Sept 1997    Vmalloc internal stack as needed.
  34  *                                      Cope with changing max_files.
  35  *      Al Viro         11 Oct 1998
  36  *              Graph may have cycles. That is, we can send the descriptor
  37  *              of foo to bar and vice versa. Current code chokes on that.
  38  *              Fix: move SCM_RIGHTS ones into the separate list and then
  39  *              skb_free() them all instead of doing explicit fput's.
  40  *              Another problem: since fput() may block somebody may
  41  *              create a new unix_socket when we are in the middle of sweep
  42  *              phase. Fix: revert the logic wrt MARKED. Mark everything
  43  *              upon the beginning and unmark non-junk ones.
  44  *
  45  *              [12 Oct 1998] AAARGH! New code purges all SCM_RIGHTS
  46  *              sent to connect()'ed but still not accept()'ed sockets.
  47  *              Fixed. Old code had slightly different problem here:
  48  *              extra fput() in situation when we passed the descriptor via
  49  *              such socket and closed it (descriptor). That would happen on
  50  *              each unix_gc() until the accept(). Since the struct file in
  51  *              question would go to the free list and might be reused...
  52  *              That might be the reason of random oopses on filp_close()
  53  *              in unrelated processes.
  54  *
  55  *      AV              28 Feb 1999
  56  *              Kill the explicit allocation of stack. Now we keep the tree
  57  *              with root in dummy + pointer (gc_current) to one of the nodes.
  58  *              Stack is represented as path from gc_current to dummy. Unmark
  59  *              now means "add to tree". Push == "make it a son of gc_current".
  60  *              Pop == "move gc_current to parent". We keep only pointers to
  61  *              parents (->gc_tree).
  62  *      AV              1 Mar 1999
  63  *              Damn. Added missing check for ->dead in listen queues scanning.
  64  *
  65  */
  66
  67 #include <linux/kernel.h>
  68 #include <linux/sched.h>
  69 #include <linux/string.h>
  70 #include <linux/socket.h>
  71 #include <linux/un.h>
  72 #include <linux/net.h>
  73 #include <linux/fs.h>
  74 #include <linux/slab.h>
  75 #include <linux/skbuff.h>
  76 #include <linux/netdevice.h>
  77 #include <linux/file.h>
  78 #include <linux/proc_fs.h>
  79 #include <linux/mutex.h>
  80
  81 #include <net/sock.h>
  82 #include <net/af_unix.h>
  83 #include <net/scm.h>
  84 #include <net/tcp_states.h>
  85
  86 /* Internal data structures and random procedures: */
  87
  88 #define GC_HEAD         ((struct sock *)(-1))
  89 #define GC_ORPHAN       ((struct sock *)(-3))
  90
  91 static struct sock *gc_current = GC_HEAD; /* stack of objects to mark */
  92
  93 atomic_t unix_tot_inflight = ATOMIC_INIT(0);
  94
  95
  96 static struct sock *unix_get_socket(struct file *filp)
  97 {
  98         struct sock *u_sock = NULL;
  99         struct inode *inode = filp->f_dentry->d_inode;
 100
 101         /*
 102          *      Socket ?
 103          */
 104         if (S_ISSOCK(inode->i_mode)) {
 105                 struct socket * sock = SOCKET_I(inode);
 106                 struct sock * s = sock->sk;
 107
 108                 /*
 109                  *      PF_UNIX ?
 110                  */
 111                 if (s && sock->ops && sock->ops->family == PF_UNIX)
 112                         u_sock = s;
 113         }
 114         return u_sock;
 115 }
 116
 117 /*
 118  *      Keep the number of times in flight count for the file
 119  *      descriptor if it is for an AF_UNIX socket.
 120  */
 121
 122 void unix_inflight(struct file *fp)
 123 {
 124         struct sock *s = unix_get_socket(fp);
 125         if(s) {
 126                 atomic_inc(&unix_sk(s)->inflight);
 127                 atomic_inc(&unix_tot_inflight);
 128         }
 129 }
 130
 131 void unix_notinflight(struct file *fp)
 132 {
 133         struct sock *s = unix_get_socket(fp);
 134         if(s) {
 135                 atomic_dec(&unix_sk(s)->inflight);
 136                 atomic_dec(&unix_tot_inflight);
 137         }
 138 }
 139
 140
 141 /*
 142  *      Garbage Collector Support Functions
 143  */
 144
 145 static inline struct sock *pop_stack(void)
 146 {
 147         struct sock *p = gc_current;
 148         gc_current = unix_sk(p)->gc_tree;
 149         return p;
 150 }
 151
 152 static inline int empty_stack(void)
 153 {
 154         return gc_current == GC_HEAD;
 155 }
 156
 157 static void maybe_unmark_and_push(struct sock *x)
 158 {
 159         struct unix_sock *u = unix_sk(x);
 160
 161         if (u->gc_tree != GC_ORPHAN)
 162                 return;
 163         sock_hold(x);
 164         u->gc_tree = gc_current;
 165         gc_current = x;
 166 }
 167
 168
 169 /* The external entry point: unix_gc() */
 170
 171 void unix_gc(void)
 172 {
 173         static DEFINE_MUTEX(unix_gc_sem);
 174         int i;
 175         struct sock *s;
 176         struct sk_buff_head hitlist;
 177         struct sk_buff *skb;
 178
 179         /*
 180          *      Avoid a recursive GC.
 181          */
 182
 183         if (!mutex_trylock(&unix_gc_sem))
 184                 return;
 185
 186         spin_lock(&unix_table_lock);
 187
 188         forall_unix_sockets(i, s)
 189         {
 190                 unix_sk(s)->gc_tree = GC_ORPHAN;
 191         }
 192         /*
 193          *      Everything is now marked
 194          */
 195
 196         /* Invariant to be maintained:
 197                 - everything unmarked is either:
 198                 -- (a) on the stack, or
 199                 -- (b) has all of its children unmarked
 200                 - everything on the stack is always unmarked
 201                 - nothing is ever pushed onto the stack twice, because:
 202                 -- nothing previously unmarked is ever pushed on the stack
 203          */
 204
 205         /*
 206          *      Push root set
 207          */
 208
 209         forall_unix_sockets(i, s)
 210         {
 211                 int open_count = 0;
 212
 213                 /*
 214                  *      If all instances of the descriptor are not
 215                  *      in flight we are in use.
 216                  *
 217                  *      Special case: when socket s is embrion, it may be
 218                  *      hashed but still not in queue of listening socket.
 219                  *      In this case (see unix_create1()) we set artificial
 220                  *      negative inflight counter to close race window.
 221                  *      It is trick of course and dirty one.
 222                  */
 223                 if (s->sk_socket && s->sk_socket->file)
 224                         open_count = file_count(s->sk_socket->file);
 225                 if (open_count > atomic_read(&unix_sk(s)->inflight))
 226                         maybe_unmark_and_push(s);
 227         }
 228
 229         /*
 230          *      Mark phase
 231          */
 232
 233         while (!empty_stack())
 234         {
 235                 struct sock *x = pop_stack();
 236                 struct sock *sk;
 237
 238                 spin_lock(&x->sk_receive_queue.lock);
 239                 skb = skb_peek(&x->sk_receive_queue);
 240
 241                 /*
 242                  *      Loop through all but first born
 243                  */
 244
 245                 while (skb && skb != (struct sk_buff *)&x->sk_receive_queue) {
 246                         /*
 247                          *      Do we have file descriptors ?
 248                          */
 249                         if(UNIXCB(skb).fp)
 250                         {
 251                                 /*
 252                                  *      Process the descriptors of this socket
 253                                  */
 254                                 int nfd=UNIXCB(skb).fp->count;
 255                                 struct file **fp = UNIXCB(skb).fp->fp;
 256                                 while(nfd--)
 257                                 {
 258                                         /*
 259                                          *      Get the socket the fd matches if
 260                                          *      it indeed does so
 261                                          */
 262                                         if((sk=unix_get_socket(*fp++))!=NULL)
 263                                         {
 264                                                 maybe_unmark_and_push(sk);
 265                                         }
 266                                 }
 267                         }
 268                         /* We have to scan not-yet-accepted ones too */
 269                         if (x->sk_state == TCP_LISTEN)
 270                                 maybe_unmark_and_push(skb->sk);
 271                         skb=skb->next;
 272                 }
 273                 spin_unlock(&x->sk_receive_queue.lock);
 274                 sock_put(x);
 275         }
 276
 277         skb_queue_head_init(&hitlist);
 278
 279         forall_unix_sockets(i, s)
 280         {
 281                 struct unix_sock *u = unix_sk(s);
 282
 283                 if (u->gc_tree == GC_ORPHAN) {
 284                         struct sk_buff *nextsk;
 285
 286                         spin_lock(&s->sk_receive_queue.lock);
 287                         skb = skb_peek(&s->sk_receive_queue);
 288                         while (skb &&
 289                                skb != (struct sk_buff *)&s->sk_receive_queue) {
 290                                 nextsk = skb->next;
 291                                 /*
 292                                  *      Do we have file descriptors ?
 293                                  */
 294                                 if (UNIXCB(skb).fp) {
 295                                         __skb_unlink(skb,
 296                                                      &s->sk_receive_queue);
 297                                         __skb_queue_tail(&hitlist, skb);
 298                                 }
 299                                 skb = nextsk;
 300                         }
 301                         spin_unlock(&s->sk_receive_queue.lock);
 302                 }
 303                 u->gc_tree = GC_ORPHAN;
 304         }
 305         spin_unlock(&unix_table_lock);
 306
 307         /*
 308          *      Here we are. Hitlist is filled. Die.
 309          */
 310
 311         __skb_queue_purge(&hitlist);
 312         mutex_unlock(&unix_gc_sem);
 313 }