SCPLock.c   [plain text]

/*
 * Copyright (c) 2000, 2001, 2004-2010 Apple Inc. All rights reserved.
 *
 * @APPLE_LICENSE_HEADER_START@
 * 
 * This file contains Original Code and/or Modifications of Original Code
 * as defined in and that are subject to the Apple Public Source License
 * Version 2.0 (the 'License'). You may not use this file except in
 * compliance with the License. Please obtain a copy of the License at
 * http://www.opensource.apple.com/apsl/ and read it before using this
 * file.
 * 
 * The Original Code and all software distributed under the License are
 * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
 * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
 * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
 * Please see the License for the specific language governing rights and
 * limitations under the License.
 * 
 * @APPLE_LICENSE_HEADER_END@
 */

/*
 * Modification History
 *
 * June 1, 2001			Allan Nathanson <ajn@apple.com>
 * - public API conversion
 *
 * November 9, 2000		Allan Nathanson <ajn@apple.com>
 * - initial revision
 */

#include <TargetConditionals.h>
#include <SystemConfiguration/SystemConfiguration.h>
#include <SystemConfiguration/SCPrivate.h>
#include "SCPreferencesInternal.h"
#include "SCHelper_client.h"

#include <grp.h>
#include <fcntl.h>
#include <stdio.h>
#include <unistd.h>
#include <pthread.h>
#include <sys/attr.h>
#include <sys/errno.h>
#include <sys/mount.h>
#include <sys/param.h>



static Boolean
__SCPreferencesLock_helper(SCPreferencesRef prefs, Boolean wait)
{
	Boolean			ok;
	SCPreferencesPrivateRef	prefsPrivate	= (SCPreferencesPrivateRef)prefs;
	uint32_t		status		= kSCStatusOK;
	CFDataRef		reply		= NULL;

	if (prefsPrivate->helper_port == MACH_PORT_NULL) {
		ok = __SCPreferencesCreate_helper(prefs);
		if (!ok) {
			return FALSE;
		}
	}

	// have the helper "lock" the prefs
	status = kSCStatusOK;
	reply  = NULL;
	ok = _SCHelperExec(prefsPrivate->helper_port,
			   wait ? SCHELPER_MSG_PREFS_LOCKWAIT : SCHELPER_MSG_PREFS_LOCK,
			   prefsPrivate->signature,
			   &status,
			   NULL);
	if (!ok) {
		goto fail;
	}

	if (status != kSCStatusOK) {
		goto error;
	}

	prefsPrivate->locked = TRUE;
	return TRUE;

    fail :

	// close helper
	if (prefsPrivate->helper_port != MACH_PORT_NULL) {
		_SCHelperClose(&prefsPrivate->helper_port);
	}

	status = kSCStatusAccessError;

    error :

	// return error
	_SCErrorSet(status);
	return FALSE;
}


static int
createParentDirectory(const char *path)
{
	char	dir[PATH_MAX];
	int	ret;
	char	*scan;
	char	*slash;

	// get parent directory path
	if (strlcpy(dir, path, sizeof(dir)) >= sizeof(dir)) {
		errno = ENOENT;
		return -1;
	}

	slash = strrchr(dir, '/');
	if ((slash == NULL) || (slash == dir)) {
		errno = ENOENT;
		return -1;
	}
	*slash = '\0';

	// create parent directories
	for (scan = dir; TRUE; scan = slash) {
		mode_t	mode	= S_IRWXU|S_IRGRP|S_IXGRP|S_IROTH|S_IXOTH;	// 755
		char	sep	= '\0';

		if (slash != NULL) {
			sep = *slash;
			*slash = '\0';
		}

		ret = mkdir(dir, mode);
		if (ret == 0) {
			static	gid_t	group	= -1;

			// set group
			if (group == -1) {
				char		buf[256];
				struct group	grp;
				struct group	*grpP	= NULL;

				if ((getgrnam_r("wheel", &grp, buf, sizeof(buf), &grpP) == 0) &&
				    (grpP != NULL)) {
					group = grpP->gr_gid;
				} else {
					SCLog(TRUE, LOG_ERR,
					      CFSTR("SCPreferencesLock getgrnam_r() failed: %s"),
					      strerror(errno));
					group = 0;	// wheel
				}
			}

			if (chown(dir, -1, group) == -1) {
				SCLog(TRUE, LOG_ERR,
				      CFSTR("SCPreferencesLock chown() failed: %s"),
				      strerror(errno));
			}

			// set [force] mode
			if (chmod(dir, mode) == -1) {
				SCLog(TRUE, LOG_ERR,
				      CFSTR("SCPreferencesLock chmod() failed: %s"),
				      strerror(errno));
			}

			if ((slash == NULL) || (scan == dir)) {
				return 0;
			}
		} else if ((errno == ENOENT) && (scan == dir)) {
			// the initial mkdir (of the full dir path) can fail
			;
		} else if (errno == EROFS) {
			return -1;
		} else if (errno != EEXIST) {
			break;
		}

		if (slash != NULL) {
			*slash = sep;
		} else {
			break;
		}
		slash = strchr(scan + 1, '/');
	}

	SCLog(TRUE, LOG_ERR,
	      CFSTR("SCPreferencesLock mkdir() failed: %s"),
	      strerror(errno));
	return -1;
}


static void
reportDelay(SCPreferencesRef prefs, struct timeval *delay, Boolean isStale)
{
	aslmsg			m;
	SCPreferencesPrivateRef	prefsPrivate	= (SCPreferencesPrivateRef)prefs;
	char			str[256];

	m = asl_new(ASL_TYPE_MSG);
	asl_set(m, "com.apple.message.domain", "com.apple.SystemConfiguration.SCPreferencesLock");
	(void) _SC_cfstring_to_cstring(prefsPrivate->name, str, sizeof(str), kCFStringEncodingUTF8);
	asl_set(m, "com.apple.message.signature", str);
	(void) _SC_cfstring_to_cstring(prefsPrivate->prefsID, str, sizeof(str), kCFStringEncodingUTF8);
	asl_set(m, "com.apple.message.signature2", str);
	(void) snprintf(str, sizeof(str),
			"%d.%3.3d",
			(int)delay->tv_sec,
			delay->tv_usec / 1000);
	asl_set(m, "com.apple.message.value", str);
	SCLOG(NULL, m, ASL_LEVEL_DEBUG,
	      CFSTR("SCPreferences(%@:%@) lock delayed for %d.%3.3d seconds%s"),
	      prefsPrivate->name,
	      prefsPrivate->prefsID,
	      (int)delay->tv_sec,
	      delay->tv_usec / 1000,
	      isStale ? " (stale)" : "");
	asl_free(m);

	return;
}


static Boolean
has_O_EXLOCK(SCPreferencesPrivateRef prefsPrivate)
{
#pragma pack(push, 4)
	struct {
		u_int32_t		size;
		vol_capabilities_attr_t	capabilities;
	} attrbuf;
#pragma pack(pop)
	struct attrlist			attrs;
	int				fd;
	int				ret;
	struct statfs			statbuf;

	fd = open(prefsPrivate->lockPath, O_WRONLY|O_CREAT, 0644);
	if (fd == -1) {
		SCLog(TRUE, LOG_ERR,
		      CFSTR("SCPreferencesLock open() failed: %s"),
		      strerror(errno));
		return FALSE;
	}

	ret = fstatfs(fd, &statbuf);
	unlink(prefsPrivate->lockPath);
	close(fd);
	if (ret == -1) {
		SCLog(TRUE, LOG_ERR,
		      CFSTR("SCPreferencesLock fstatfs() failed: %s"),
		      strerror(errno));
		return FALSE;
	}

	bzero(&attrs, sizeof(attrs));
	attrs.bitmapcount = ATTR_BIT_MAP_COUNT;
	attrs.volattr     = ATTR_VOL_INFO | ATTR_VOL_CAPABILITIES;
	bzero(&attrbuf, sizeof(attrbuf));
	ret = getattrlist(statbuf.f_mntonname,	// path (of mount point)
			  &attrs,		// attribute list
			  &attrbuf,		// attribute buffer
			  sizeof(attrbuf),
			  0);			// options
	if (ret == -1) {
		SCLog(TRUE, LOG_ERR,
		      CFSTR("SCPreferencesLock getattrlist() failed: %s"),
		      strerror(errno));
		return FALSE;
	}

	if ((attrbuf.capabilities.capabilities[VOL_CAPABILITIES_INTERFACES] & VOL_CAP_INT_FLOCK) &&
	    (attrbuf.capabilities.valid       [VOL_CAPABILITIES_INTERFACES] & VOL_CAP_INT_FLOCK)) {
		return TRUE;
	}

	return FALSE;
}


static Boolean
lockWithSCDynamicStore(SCPreferencesPrivateRef	prefsPrivate, Boolean wait)
{
	CFArrayRef	changes;
	Boolean		locked		= FALSE;
	Boolean		ok;
	int		sc_status	= kSCStatusOK;

	// add [lock] notification
	ok = SCDynamicStoreAddWatchedKey(prefsPrivate->session,
					 prefsPrivate->sessionKeyLock,
					 FALSE);
	if (!ok) {
		sc_status = SCError();
		SCLog(_sc_verbose, LOG_ERR, CFSTR("SCPreferencesLock SCDynamicStoreAddWatchedKey() failed"));
	}

	while (ok) {
		CFDateRef	value;

		// Attempt to acquire the lock
		value = CFDateCreate(NULL, CFAbsoluteTimeGetCurrent());
		ok = SCDynamicStoreAddTemporaryValue(prefsPrivate->session,
						     prefsPrivate->sessionKeyLock,
						     value);
		CFRelease(value);
		if (ok) {
			locked = TRUE;
			break;
		}

		if (!wait) {
			sc_status = kSCStatusPrefsBusy;
			break;
		}

		// wait for the lock to be released
		ok = SCDynamicStoreNotifyWait(prefsPrivate->session);
		if (!ok) {
			sc_status = SCError();
			SCLog(_sc_verbose, LOG_ERR, CFSTR("SCPreferencesLock SCDynamicStoreNotifyWait() failed"));
			break;
		}

		// clear out any notifications
		changes = SCDynamicStoreCopyNotifiedKeys(prefsPrivate->session);
		if (changes != NULL) {
			CFRelease(changes);
		} else {
			SCLog(_sc_verbose, LOG_ERR, CFSTR("SCPreferencesLock SCDynamicStoreCopyNotifiedKeys() failed"));
			break;
		}
	}

	// remove [lock] notification
	(void) SCDynamicStoreRemoveWatchedKey(prefsPrivate->session,
					      prefsPrivate->sessionKeyLock,
					      0);

	// clear out any notifications
	changes = SCDynamicStoreCopyNotifiedKeys(prefsPrivate->session);
	if (changes != NULL) {
		CFRelease(changes);
	}

	if (sc_status != kSCStatusOK) {
		_SCErrorSet(sc_status);
	}
	return locked;
}


Boolean
SCPreferencesLock(SCPreferencesRef prefs, Boolean wait)
{
	char			buf[32];
	struct timeval		lockStart;
	struct timeval		lockElapsed;
	SCPreferencesPrivateRef	prefsPrivate	= (SCPreferencesPrivateRef)prefs;
	int			sc_status	= kSCStatusFailed;
	struct stat		statBuf;
	struct stat		statBuf2;

	if (prefs == NULL) {
		/* sorry, you must provide a session */
		_SCErrorSet(kSCStatusNoPrefsSession);
		return FALSE;
	}

	if (prefsPrivate->locked) {
		/* sorry, you already have the lock */
		_SCErrorSet(kSCStatusLocked);
		return FALSE;
	}

	if (prefsPrivate->authorizationData != NULL) {
		return __SCPreferencesLock_helper(prefs, wait);
	}

	if (!prefsPrivate->isRoot) {
		_SCErrorSet(kSCStatusAccessError);
		return FALSE;
	}


	pthread_mutex_lock(&prefsPrivate->lock);

	if (prefsPrivate->session == NULL) {
		__SCPreferencesAddSession(prefs);
	}

	if (prefsPrivate->lockPath == NULL) {
		char	*path;
		int	pathLen;

		path = prefsPrivate->newPath ? prefsPrivate->newPath : prefsPrivate->path;
		pathLen = strlen(path) + sizeof("-lock");
		prefsPrivate->lockPath = CFAllocatorAllocate(NULL, pathLen, 0);
		snprintf(prefsPrivate->lockPath, pathLen, "%s-lock", path);
	}

	(void)gettimeofday(&lockStart, NULL);

    retry :

	if (prefsPrivate->sessionKeyLock != NULL) {
		if (lockWithSCDynamicStore(prefsPrivate, wait)) {
			goto locked;
		}

		goto error;
	}

	prefsPrivate->lockFD = open(prefsPrivate->lockPath,
				    wait ? O_WRONLY|O_CREAT|O_EXLOCK
					 : O_WRONLY|O_CREAT|O_EXLOCK|O_NONBLOCK,
				    0644);
	if (prefsPrivate->lockFD == -1) {
		switch (errno) {
			case ENOENT :
				if ((prefsPrivate->prefsID == NULL) ||
				    !CFStringHasPrefix(prefsPrivate->prefsID, CFSTR("/"))) {
					int	ret;

					// create parent (/Library/Preferences/SystemConfiguration)
					ret = createParentDirectory(prefsPrivate->lockPath);
					if (ret == 0) {
						SCLog(TRUE, LOG_NOTICE,
						      CFSTR("created directory for \"%s\""),
						      prefsPrivate->newPath ? prefsPrivate->newPath : prefsPrivate->path);
						goto retry;
					} else if (errno == EROFS) {
						goto locked;
					}
				}
				break;
			case EROFS :
				// if read-only filesystem
				goto locked;
			case EWOULDBLOCK :
				// if already locked (and we are not blocking)
				sc_status = kSCStatusPrefsBusy;
				goto error;
			case ENOTSUP :
				if (!has_O_EXLOCK(prefsPrivate)) {
					// O_EXLOCK *not* available, use SCDynamicStore
					prefsPrivate->sessionKeyLock = _SCPNotificationKey(NULL,
											   prefsPrivate->prefsID,
											   kSCPreferencesKeyLock);
					goto retry;
				}
				errno = ENOTSUP;
				break;
			default :
				break;
		}

		sc_status = errno;
		SCLog(TRUE, LOG_ERR,
		      CFSTR("SCPreferencesLock open() failed: %s"),
		      strerror(errno));
		goto error;
	}

	if ((stat(prefsPrivate->lockPath, &statBuf) == -1) ||
	    (fstat(prefsPrivate->lockFD, &statBuf2) == -1) ||
	    (statBuf.st_dev != statBuf2.st_dev) ||
	    (statBuf.st_ino != statBuf2.st_ino)) {
		// if the lock file was unlinked or re-created
		close(prefsPrivate->lockFD);
		prefsPrivate->lockFD = -1;
		goto retry;
	}

	// we have the lock

	snprintf(buf, sizeof(buf), "%d\n", getpid());
	write(prefsPrivate->lockFD, buf, strlen(buf));

    locked :

	(void)gettimeofday(&prefsPrivate->lockTime, NULL);
	timersub(&prefsPrivate->lockTime, &lockStart, &lockElapsed);

	if (prefsPrivate->accessed) {
		CFDataRef       currentSignature;
		Boolean		match;

		/*
		 * the preferences have been accessed since the
		 * session was created so we need to compare
		 * the signature of the stored preferences.
		 */
		if (stat(prefsPrivate->path, &statBuf) == -1) {
			if (errno == ENOENT) {
				bzero(&statBuf, sizeof(statBuf));
			} else {
				SCLog(TRUE, LOG_DEBUG,
				      CFSTR("SCPreferencesLock stat() failed: %s"),
				      strerror(errno));
				goto stale;
			}
		}

		currentSignature = __SCPSignatureFromStatbuf(&statBuf);
		match = CFEqual(prefsPrivate->signature, currentSignature);
		CFRelease(currentSignature);
		if (!match) {
			/*
			 * the preferences have been updated since the
			 * session was accessed so we've got no choice
			 * but to deny the lock request.
			 */
			goto stale;
		}
//	} else {
//		/*
//		 * the file contents have changed but since we
//		 * haven't accessed any of the preference data we
//		 * don't need to return an error.  Simply proceed.
//		 */
	}

	if (lockElapsed.tv_sec > 0) {
		// if we waited more than 1 second to acquire the lock
		reportDelay(prefs, &lockElapsed, FALSE);
	}

	prefsPrivate->locked = TRUE;
	pthread_mutex_unlock(&prefsPrivate->lock);
	return TRUE;

    stale :

	sc_status = kSCStatusStale;
	unlink(prefsPrivate->lockPath);

	if (lockElapsed.tv_sec > 0) {
		// if we waited more than 1 second to acquire the lock
		reportDelay(prefs, &lockElapsed, TRUE);
	}

    error :

	if (prefsPrivate->lockFD != -1)	{
		close(prefsPrivate->lockFD);
		prefsPrivate->lockFD = -1;
	}

	pthread_mutex_unlock(&prefsPrivate->lock);
	_SCErrorSet(sc_status);
	return FALSE;
}