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_path.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 } 314