--- /dev/null
+<?php
+/*
+ *
+ *
+ * function: nfslock
+ * original author: Chuck Cranor <chuck@maria.wustl.edu>
+ * rewritten by: Alexis Rosen <alexis@panix.com>
+ * rewritten by: Cedric Morin <cedric@yterium.com> for php&SPIP
+ *
+ * (Excerpts from Chuck's notes:
+ * this becomes complex, due to our dear friend, the NFS mounted mail spool.
+ * the netbsd code didn't do this properly, as far as I could tell.
+ *
+ * - you can't trust exclusive creating opens over NFS, the protocol
+ * just doesn't support it. so to do a lock you have to create
+ * a tmp file and then try and hard link it to your lock file.
+ * - to detect a stale lock file you have to see how old it is, but
+ * you can't use time(0) because that is the time on the local system
+ * and the file gets the times of the NFS server. when is a lock
+ * file stale? people seem to like 120 or 300 seconds.)
+ *
+ * NB: It is _critical_ that nfslock()ed files be unlocked by nfsunlock().
+ * Simply unlinking the lock file is a good way to trash someone else's lock
+ * file. All it takes is for the process doing the unlink to get hung for
+ * a few minutes when it doesn't expect it. Meanwhile, its lock expires and
+ * a second process forces the lock and creates its own. Then the first
+ * process comes along and kills the second process' lock while it's still
+ * valid.
+ *
+ * Security considerations:
+ * If we're root, be very careful to see that the temp file we opened is
+ * what we think it is. The problem is that we could lose a race with
+ * someone who takes our tmp file and replaces it with, say, a hard
+ * link to /etc/passwd. Then, if the first lock attempt fails, we'll
+ * write a char to the file (see 4. below); this would truncate the
+ * passwd file. So we make sure that the link count is 1. We don't really
+ * care about any other screwing around since we don't write anything
+ * sensitive to the lock file, nor do we change its owner or mode. If
+ * someone beats us on a race and replaces our temp file with anything
+ * else, it's no big deal- the file may get truncated, but there's no
+ * possible security breach. ...Actually the possibility of the race
+ * ever happening, given the random name of the file, is virtually nil.
+ *
+ * args: path = path to directory of lock file (/net/u/1/a/alexis/.mailspool)
+ * namelock = file name of lock file (alexis.lock)
+ * max_age = age of lockfile, in seconds, after which the lock is stale.
+ * stale locks are always broken. Defaults to DEFAULT_LOCKTIME
+ * if zero. Panix mail locks go stale at 300 seconds, the default.
+ * notify = 1 if we should tell stdout that we're sleeping on a lock
+ *
+ * Returns the time that the lock was created on the other system. This is
+ * important for nfsunlock(). If the lock already exists, returns NFSL_LOCKED.
+ * If there is some other failure, return NFSL_SYSF. If NFSL_LOCKED is
+ * returned, errno is also set to EEXIST. If we're root and the link count
+ * on the tmp file is wrong, return NFSL_SECV.
+ *
+ * Mods of 7/13/95: Change a bit of code to re-stat the lockfile after
+ * closing it. This is to work around a bug in SunOS that appears to to affect
+ * some SunOS 4.1.3 machines (but not all). The bug is that close() updates
+ * the stat st_ctime field for that file. So use lstat on fullpath instead
+ * of fstat on tmpfd. This alteration applies to both nfslock and nfslock1.
+ *
+ * Mod of 5/4/95: Change printf's to fprintf(stderr... in nfslock and nfslock1.
+ *
+ * Mods of 4/29/95: Fix freeing memory before use if a stat fails. Remove
+ * code that forbids running as root; instead, if root, check link count on
+ * tmp file after opening it.
+ *
+ * Mods of 4/27/95: Return the create time instead of the lockfile's fd, which
+ * is useless. Added new routines nfsunlock(), nfslock_test(), nfslock_renew().
+ *
+ * Mods of 1/8/95: Eliminate some security checks since this code never
+ * runs as root. In particular, we completely eliminate the safeopen
+ * routine. But add one check: if we _are_ root, fail immediately.
+ *
+ * Change arguments: take a path and a filename. Don't assume a global or
+ * macro pointing to a mailspool.
+ *
+ * Add notify argument; if 1, tell user when we're waiting for a lock.
+ *
+ * Add max_age argument and DEFAULT_LOCKTIME.
+ *
+ * Change comments drastically.
+ *
+ */
+
+if (!defined('_ECRIRE_INC_VERSION')) return;
+
+include_spip('inc/acces');
+define('_DEFAULT_LOCKTIME',60);
+define('_NAME_LOCK','spip_nfs_lock');
+
+// http://doc.spip.org/@spip_nfslock
+function spip_nfslock($fichier,$max_age=0) {
+ $tries = 0;
+
+ if (!$max_age) $max_age = _DEFAULT_LOCKTIME;
+ $lock_file = _DIR_TMP . _NAME_LOCK . "-" . substr(md5($fichier),0,8);
+
+
+ /*
+ * 1. create a tmp file with a psuedo random file name. we also make
+ * tpath which is a buffer to store the full pathname of the tmp file.
+ */
+
+ $id = creer_uniqid();
+ $tpath = _DIR_TMP."slock.$id";
+ $tmpfd = @fopen($tpath, 'w'); // hum, le 'x' necessite php4,3,2 ...
+ if (!$tmpfd) { /* open failed */
+ @fclose($tmpfd);
+ spip_unlink($tpath);
+ return false; //NFSL_SYSF
+ }
+
+ /*
+ * 2. make fullpath, a buffer for the full pathname of the lock file.
+ * then start looping trying to lock it
+ */
+
+ while ($tries < 10) {
+ /*
+ * 3. link tmp file to lock file. if it goes, we win and we clean
+ * up and return the st_ctime of the lock file.
+ */
+
+ if (link($tpath, $lock_file) == 1) {
+ spip_unlink($tpath); /* got it! */
+ @fclose($tmpfd);
+ if (($our_tmp = lstat($lock_file))==false) { /* stat failed... shouldn't happen */
+ spip_unlink($lock_file);
+ return false; // (NFSL_SYSF);
+ }
+ return($our_tmp['ctime']);
+ }
+
+ /*
+ * 4. the lock failed. check for a stale lock file, being mindful
+ * of NFS and the fact the time is set from the NFS server. we
+ * do a write on the tmp file to update its time to the server's
+ * idea of "now."
+ */
+
+ $old_stat = lstat($lock_file);
+ if (@fputs($tmpfd, "zz", 2)!=2 || !$our_tmp=fstat($tmpfd))
+ break; /* something bogus is going on */
+
+
+ if ($old_stat!=false && (($old_stat['ctime'] + $max_age) < $our_tmp['ctime'])) {
+ spip_unlink($lock_file); /* break the stale lock */
+ $tries++;
+ /* It is CRITICAL that we sleep after breaking
+ * the lock. Otherwise, we could race with
+ * another process and unlink it's newly-
+ * created file.
+ */
+ sleep(1+rand(0,4));
+ continue;
+ }
+
+ /*
+ * 5. try again
+ */
+
+ $tries++;
+ sleep(1+rand(0,4));
+ }
+
+ /*
+ * 6. give up, failure.
+ */
+
+ spip_unlink($tpath);
+ @fclose($tmpfd);
+ return false; //(NFSL_LOCKED);
+}
+
+/*
+ * function: nfsunlock
+ * author: Alexis Rosen <alexis@panix.com>
+ *
+ * Unlock an nfslock()ed file.
+ *
+ * This can get tricky because the lock may have expired (perhaps even
+ * during a process that should be "atomic"). We have to make sure we don't
+ * unlock some other process' lock, and return a panic code if we think our
+ * lock file has been broken illegally. What's done in reaction to that panic
+ * (of anything) is up to the caller. See the comments on nfslock()!
+ *
+ * args: path = path to directory of lock file (/net/u/1/a/alexis/.mailspool)
+ * namelock = file name of lock file (alexis.lock)
+ * max_age = age of lockfile, in seconds, after which the lock is stale.
+ * stale locks are always broken. Defaults to DEFAULT_LOCKTIME
+ * if zero. Panix mail locks go stale at 300 seconds, the default.
+ * birth = time the lock was created (as returned by nfslock()).
+ *
+ * Returns NFSL_OK if successful, NFSL_LOST if the lock has been lost
+ * legitimately (because more than max_age has passed since the lock was
+ * created), and NFSL_STOLEN if it's been tampered with illegally (i.e.
+ * while this program is within the expiry period). Returns NFSL_SYSF if
+ * another system failure prevents it from even trying to unlock the file.
+ *
+ * Note that for many programs, a return code of NFSL_LOST or NFSL_STOLEN is
+ * equally disastrous; a NFSL_STOLEN means that some other program may have
+ * trashed your file, but a NFSL_LOST may mean that _you_ have trashed someone
+ * else's file (if in fact you wrote the file that you locked after you lost
+ * the lock) or that you read inconsistent information.
+ *
+ * In practice, a return code of NFSL_LOST or NFSL_STOLEN will virtually never
+ * happen unless someone is violating the locking protocol.
+ *
+ */
+
+// http://doc.spip.org/@spip_nfsunlock
+function spip_nfsunlock($fichier, $birth, $max_age=0, $test = false) {
+ $id = creer_uniqid();
+ if (!$max_age) $max_age = _DEFAULT_LOCKTIME;
+
+ /*
+ * 1. Build a temp file and stat that to get an idea of what the server
+ * thinks the current time is (our_tmp.st_ctime)..
+ */
+
+ $tpath = _DIR_TMP."stime.$id";
+ $tmpfd = @fopen($tpath,'w');
+ if ((!$tmpfd)
+ OR (@fputs($tmpfd, "zz", 2) != 2)
+ OR !($our_tmp = fstat($tmpfd))) {
+ /* The open failed, or we can't write the file, or we can't stat it */
+ @fclose($tmpfd);
+ spip_unlink($tpath);
+ return false; //(NFSL_SYSF);
+ }
+
+ @fclose($tmpfd); /* We don't need this once we have our_tmp.st_ctime. */
+ spip_unlink($tpath);
+
+ /*
+ * 2. make fullpath, a buffer for the full pathname of the lock file
+ */
+
+ $lock_file = _DIR_TMP . _NAME_LOCK . "-" . substr(md5($fichier),0,8);
+
+ /*
+ * 3. If the ctime hasn't been modified, unlink the file and return. If the
+ * lock has expired, sleep the usual random interval before returning.
+ * If we didn't sleep, there could be a race if the caller immediately
+ * tries to relock the file.
+ */
+
+ if ( ($old_stat=@lstat($lock_file)) /* stat succeeds so file is there */
+ && ($old_stat['ctime'] == $birth)) { /* hasn't been modified since birth */
+ if (!$test)
+ spip_unlink($lock_file); /* so the lock is ours to remove */
+ if ($our_tmp['ctime'] >= $birth + $max_age){ /* the lock has expired */
+ if (!$test) return false; //(NFSL_LOST);
+ sleep(1+(random(0,4))); /* so sleep a bit */
+ }
+ return true;//(NFSL_OK); /* success */
+ }
+
+ /*
+ * 4. Either ctime has been modified, or the entire lock file is missing.
+ * If the lock should still be ours, based on the ctime of the temp
+ * file, return with NFSL_STOLEN. If not, then our lock is expired and
+ * someone else has grabbed the file, so return NFSL_LOST.
+ */
+
+ if ($our_tmp['ctime'] < $birth + $max_age) /* lock was stolen */
+ return false; //(NFSL_STOLEN);
+
+ return false; //(NFSL_LOST); /* The lock must have expired first. */
+}
+
+
+/*
+ * function: nfslock_test
+ * author: Alexis Rosen <alexis@panix.com>
+ *
+ * Test a lock to see if it's still valid.
+ *
+ * See the comments in nfsunlock() about lost and stolen locks.
+ *
+ * Args, return codes, and behavior are identical to nfsunlock except
+ * that nfslock_test doesn't remove the lock. NFSL_OK means the lock is
+ * good, NFLS_LOST and NFSL_STOLEN means it's bad, and NFSL_SYSF means
+ * we couldn't tell due to system failure.
+ *
+ * The source for this routine is almost identical to nfsunlock(), but it's
+ * coded separately to make things as clear as possible.
+ */
+
+// http://doc.spip.org/@spip_nfslock_test
+function spip_nfslock_test($fichier, $birth, $max_age=0) {
+ return spip_nfsunlock($fichier, $birth, $max_age, true);
+}
+
+?>
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