1 files changed, 409 insertions, 120 deletions

diff --git a/libmisc/find_new_uid.c b/libmisc/find_new_uid.c
index aac1909c..b3143134 100644
--- a/libmisc/find_new_uid.c
+++ b/libmisc/find_new_uid.c
@@ -1,6 +1,7 @@
 /*
  * Copyright (c) 1991 - 1994, Julianne Frances Haugh
  * Copyright (c) 2008 - 2011, Nicolas François
+ * Copyright (c) 2014, Red Hat, Inc.
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
@@ -39,6 +40,117 @@
 #include "getdef.h"
 
 /*
+ * get_ranges - Get the minimum and maximum ID ranges for the search
+ *
+ * This function will return the minimum and maximum ranges for IDs
+ *
+ * 0: The function completed successfully
+ * EINVAL: The provided ranges are impossible (such as maximum < minimum)
+ *
+ * preferred_min: The special-case minimum value for a specifically-
+ * requested ID, which may be lower than the standard min_id
+ */
+static int get_ranges (bool sys_user, uid_t *min_id, uid_t *max_id,
+			uid_t *preferred_min)
+{
+	uid_t uid_def_max = 0;
+
+	if (sys_user) {
+		/* System users */
+
+		/* A requested ID is allowed to be below the autoselect range */
+		*preferred_min = (uid_t) 1;
+
+		/* Get the minimum ID range from login.defs or default to 101 */
+		*min_id = (uid_t) getdef_ulong ("SYS_UID_MIN", 101UL);
+
+		/*
+		 * If SYS_UID_MAX is unspecified, we should assume it to be one
+		 * less than the UID_MIN (which is reserved for non-system accounts)
+		 */
+		uid_def_max = (uid_t) getdef_ulong ("UID_MIN", 1000UL) - 1;
+		*max_id = (uid_t) getdef_ulong ("SYS_UID_MAX",
+				(unsigned long) uid_def_max);
+
+		/* Check that the ranges make sense */
+		if (*max_id < *min_id) {
+			(void) fprintf (stderr,
+                            _("%s: Invalid configuration: SYS_UID_MIN (%lu), "
+                              "UID_MIN (%lu), SYS_UID_MAX (%lu)\n"),
+                            Prog, (unsigned long) *min_id,
+                            getdef_ulong ("UID_MIN", 1000UL),
+                            (unsigned long) *max_id);
+			return EINVAL;
+		}
+	} else {
+		/* Non-system users */
+
+		/* Get the values from login.defs or use reasonable defaults */
+		*min_id = (uid_t) getdef_ulong ("UID_MIN", 1000UL);
+		*max_id = (uid_t) getdef_ulong ("UID_MAX", 60000UL);
+
+		/*
+		 * The preferred minimum should match the standard ID minimum
+		 * for non-system users.
+		 */
+		*preferred_min = *min_id;
+
+		/* Check that the ranges make sense */
+		if (*max_id < *min_id) {
+			(void) fprintf (stderr,
+					_("%s: Invalid configuration: UID_MIN (%lu), "
+					  "UID_MAX (%lu)\n"),
+					Prog, (unsigned long) *min_id,
+					(unsigned long) *max_id);
+			return EINVAL;
+		}
+	}
+
+	return 0;
+}
+
+/*
+ * check_uid - See if the requested UID is available
+ *
+ * On success, return 0
+ * If the ID is in use, return EEXIST
+ * If the ID is outside the range, return ERANGE
+ * In other cases, return errno from getpwuid()
+ */
+static int check_uid(const uid_t uid,
+		     const uid_t uid_min,
+		     const uid_t uid_max,
+		     bool *used_uids)
+{
+	/* First test that the preferred ID is in the range */
+	if (uid < uid_min || uid > uid_max) {
+		return ERANGE;
+	}
+
+	/*
+	 * Check whether we already detected this UID
+	 * using the pw_next() loop
+	 */
+	if (used_uids != NULL && used_uids[uid]) {
+		return EEXIST;
+	}
+	/* Check if the UID exists according to NSS */
+	errno = 0;
+	if (getpwuid(uid) != NULL) {
+		return EEXIST;
+	} else {
+		/* getpwuid() was NULL
+		 * we have to ignore errors as temporary
+		 * failures of remote user identity services
+		 * would completely block user/group creation
+		 */
+	}
+
+	/* If we've made it here, the UID must be available */
+	return 0;
+}
+
+/*
  * find_new_uid - Find a new unused UID.
  *
  * If successful, find_new_uid provides an unused user ID in the
@@ -48,162 +160,339 @@
  * 
  * Return 0 on success, -1 if no unused UIDs are available.
  */
-int find_new_uid (bool sys_user,
-                  uid_t *uid,
-                  /*@null@*/uid_t const *preferred_uid)
+int find_new_uid(bool sys_user,
+                 uid_t *uid,
+                 /*@null@*/uid_t const *preferred_uid)
 {
-	const struct passwd *pwd;
-	uid_t uid_min, uid_max, user_id;
 	bool *used_uids;
+	const struct passwd *pwd;
+	uid_t uid_min, uid_max, preferred_min;
+	uid_t user_id, id;
+	uid_t lowest_found, highest_found;
+	int result;
+	int nospam = 0;
 
 	assert (uid != NULL);
 
-	if (!sys_user) {
-		uid_min = (uid_t) getdef_ulong ("UID_MIN", 1000UL);
-		uid_max = (uid_t) getdef_ulong ("UID_MAX", 60000UL);
-		if (uid_max < uid_min) {
-			(void) fprintf (stderr,
-			                _("%s: Invalid configuration: UID_MIN (%lu), UID_MAX (%lu)\n"),
-			                Prog, (unsigned long) uid_min, (unsigned long) uid_max);
-			return -1;
-		}
-	} else {
-		uid_min = (uid_t) getdef_ulong ("SYS_UID_MIN", 101UL);
-		uid_max = (uid_t) getdef_ulong ("UID_MIN", 1000UL) - 1;
-		uid_max = (uid_t) getdef_ulong ("SYS_UID_MAX", (unsigned long) uid_max);
-		if (uid_max < uid_min) {
-			(void) fprintf (stderr,
-			                _("%s: Invalid configuration: SYS_UID_MIN (%lu), UID_MIN (%lu), SYS_UID_MAX (%lu)\n"),
-			                Prog, (unsigned long) uid_min, getdef_ulong ("UID_MIN", 1000UL), (unsigned long) uid_max);
+	/*
+	 * First, figure out what ID range is appropriate for
+	 * automatic assignment
+	 */
+	result = get_ranges (sys_user, &uid_min, &uid_max, &preferred_min);
+	if (result == EINVAL) {
+		return -1;
+	}
+
+	/* Check if the preferred UID is available */
+	if (preferred_uid) {
+		result = check_uid (*preferred_uid, preferred_min, uid_max, NULL);
+		if (result == 0) {
+			/*
+			 * Make sure the UID isn't queued for use already
+			 */
+			if (pw_locate_uid (*preferred_uid) == NULL) {
+				*uid = *preferred_uid;
+				return 0;
+			}
+			/*
+			 * pw_locate_uid() found the UID in an as-yet uncommitted
+			 * entry. We'll proceed below and auto-set an UID.
+			 */
+		} else if (result == EEXIST || result == ERANGE) {
+			/*
+			 * Continue on below. At this time, we won't
+			 * treat these two cases differently.
+			 */
+		} else {
+			/*
+			 * An unexpected error occurred. We should report
+			 * this and fail the user creation.
+			 * This differs from the automatic creation
+			 * behavior below, since if a specific UID was
+			 * requested and generated an error, the user is
+			 * more likely to want to stop and address the
+			 * issue.
+			 */
+			fprintf (stderr,
+				_("%s: Encountered error attempting to use "
+				  "preferred UID: %s\n"),
+				Prog, strerror (result));
 			return -1;
 		}
 	}
+
+	/*
+	 * Search the entire passwd file,
+	 * looking for the next unused value.
+	 *
+	 * We first check the local database with pw_rewind/pw_next to find
+	 * all local values that are in use.
+	 *
+	 * We then compare the next free value to all databases (local and
+	 * remote) and iterate until we find a free one. If there are free
+	 * values beyond the lowest (system users) or highest (non-system
+	 * users), we will prefer those and avoid potentially reclaiming a
+	 * deleted user (which can be a security issue, since it may grant
+	 * access to files belonging to that former user).
+	 *
+	 * If there are no UIDs available at the end of the search, we will
+	 * have no choice but to iterate through the range looking for gaps.
+	 *
+	 */
+
+	/* Create an array to hold all of the discovered UIDs */
 	used_uids = malloc (sizeof (bool) * (uid_max +1));
 	if (NULL == used_uids) {
 		fprintf (stderr,
-		         _("%s: failed to allocate memory: %s\n"),
-		         Prog, strerror (errno));
+			 _("%s: failed to allocate memory: %s\n"),
+			 Prog, strerror (errno));
 		return -1;
 	}
 	memset (used_uids, false, sizeof (bool) * (uid_max + 1));
 
-	if (   (NULL != preferred_uid)
-	    && (*preferred_uid >= uid_min)
-	    && (*preferred_uid <= uid_max)
-	    /* Check if the user exists according to NSS */
-	    && (getpwuid (*preferred_uid) == NULL)
-	    /* Check also the local database in case of uncommitted
-	     * changes */
-	    && (pw_locate_uid (*preferred_uid) == NULL)) {
-		*uid = *preferred_uid;
-		free (used_uids);
-		return 0;
-	}
+	/* First look for the lowest and highest value in the local database */
+	(void) pw_rewind ();
+	highest_found = uid_min;
+	lowest_found = uid_max;
+	while ((pwd = pw_next ()) != NULL) {
+		/*
+		 * Does this entry have a lower UID than the lowest we've found
+		 * so far?
+		 */
+		if ((pwd->pw_uid <= lowest_found) && (pwd->pw_uid >= uid_min)) {
+			lowest_found = pwd->pw_uid - 1;
+		}
 
+		/*
+		 * Does this entry have a higher UID than the highest we've found
+		 * so far?
+		 */
+		if ((pwd->pw_uid >= highest_found) && (pwd->pw_uid <= uid_max)) {
+			highest_found = pwd->pw_uid + 1;
+		}
+
+		/* create index of used UIDs */
+		if (pwd->pw_uid >= uid_min
+			&& pwd->pw_uid <= uid_max) {
+
+			used_uids[pwd->pw_uid] = true;
+		}
+	}
 
-	/*
-	 * Search the entire password file,
-	 * looking for the largest unused value.
-	 *
-	 * We check the list of users according to NSS (setpwent/getpwent),
-	 * but we also check the local database (pw_rewind/pw_next) in case
-	 * some users were created but the changes were not committed yet.
-	 */
 	if (sys_user) {
-		uid_t id;
-		/* setpwent / getpwent / endpwent can be very slow with
-		 * LDAP configurations (and many accounts).
-		 * Since there is a limited amount of IDs to be tested
-		 * for system accounts, we just check the existence
-		 * of IDs with getpwuid.
+		/*
+		 * For system users, we want to start from the
+		 * top of the range and work downwards.
 		 */
-		user_id = uid_max;
-		for (id = uid_max; id >= uid_min; id--) {
-			if (getpwuid (id) != NULL) {
-				user_id = id - 1;
-				used_uids[id] = true;
-			}
+
+		/*
+		 * At the conclusion of the pw_next() search, we will either
+		 * have a presumed-free UID or we will be at UID_MIN - 1.
+		 */
+		if (lowest_found < uid_min) {
+			/*
+			 * In this case, an UID is in use at UID_MIN.
+			 *
+			 * We will reset the search to UID_MAX and proceed down
+			 * through all the UIDs (skipping those we detected with
+			 * used_uids) for a free one. It is a known issue that
+			 * this may result in reusing a previously-deleted UID,
+			 * so administrators should be instructed to use this
+			 * auto-detection with care (and prefer to assign UIDs
+			 * explicitly).
+			 */
+			lowest_found = uid_max;
 		}
 
-		(void) pw_rewind ();
-		while ((pwd = pw_next ()) != NULL) {
-			if ((pwd->pw_uid <= user_id) && (pwd->pw_uid >= uid_min)) {
-				user_id = pwd->pw_uid - 1;
-			}
-			/* create index of used UIDs */
-			if (pwd->pw_uid <= uid_max) {
-				used_uids[pwd->pw_uid] = true;
+		/* Search through all of the IDs in the range */
+		for (id = lowest_found; id >= uid_min; id--) {
+			result = check_uid (id, uid_min, uid_max, used_uids);
+			if (result == 0) {
+				/* This UID is available. Return it. */
+				*uid = id;
+				free (used_uids);
+				return 0;
+			} else if (result == EEXIST) {
+				/* This UID is in use, we'll continue to the next */
+			} else {
+				/*
+				 * An unexpected error occurred.
+				 *
+				 * Only report it the first time to avoid spamming
+				 * the logs
+				 *
+				 */
+				if (!nospam) {
+					fprintf (stderr,
+						_("%s: Can't get unique system UID (%s). "
+						  "Suppressing additional messages.\n"),
+						Prog, strerror (result));
+					SYSLOG ((LOG_ERR,
+						"Error checking available UIDs: %s",
+						strerror (result)));
+					nospam = 1;
+				}
+				/*
+				 * We will continue anyway. Hopefully a later UID
+				 * will work properly.
+				 */
 			}
 		}
-	} else {
-		user_id = uid_min;
-		setpwent ();
-		while ((pwd = getpwent ()) != NULL) {
-			if ((pwd->pw_uid >= user_id) && (pwd->pw_uid <= uid_max)) {
-				user_id = pwd->pw_uid + 1;
-			}
-			/* create index of used UIDs */
-			if (pwd->pw_uid <= uid_max) {
-				used_uids[pwd->pw_uid] = true;
+
+		/*
+		 * If we get all the way through the loop, try again from UID_MAX,
+		 * unless that was where we previously started. (NOTE: the worst-case
+		 * scenario here is that we will run through (UID_MAX - UID_MIN - 1)
+		 * cycles *again* if we fall into this case with lowest_found as
+		 * UID_MAX - 1, all users in the range in use and maintained by
+		 * network services such as LDAP.)
+		 */
+		if (lowest_found != uid_max) {
+			for (id = uid_max; id >= uid_min; id--) {
+				result = check_uid (id, uid_min, uid_max, used_uids);
+				if (result == 0) {
+					/* This UID is available. Return it. */
+					*uid = id;
+					free (used_uids);
+					return 0;
+				} else if (result == EEXIST) {
+					/* This UID is in use, we'll continue to the next */
+				} else {
+					/*
+					 * An unexpected error occurred.
+					 *
+					 * Only report it the first time to avoid spamming
+					 * the logs
+					 *
+					 */
+					if (!nospam) {
+						fprintf (stderr,
+							_("%s: Can't get unique system UID (%s). "
+							  "Suppressing additional messages.\n"),
+							Prog, strerror (result));
+						SYSLOG((LOG_ERR,
+							"Error checking available UIDs: %s",
+							strerror (result)));
+						nospam = 1;
+					}
+					/*
+					 * We will continue anyway. Hopefully a later UID
+					 * will work properly.
+					 */
+				}
 			}
 		}
-		endpwent ();
+	} else { /* !sys_user */
+		/*
+		 * For non-system users, we want to start from the
+		 * bottom of the range and work upwards.
+		 */
 
-		(void) pw_rewind ();
-		while ((pwd = pw_next ()) != NULL) {
-			if ((pwd->pw_uid >= user_id) && (pwd->pw_uid <= uid_max)) {
-				user_id = pwd->pw_uid + 1;
-			}
-			/* create index of used UIDs */
-			if (pwd->pw_uid <= uid_max) {
-				used_uids[pwd->pw_uid] = true;
-			}
+		/*
+		 * At the conclusion of the pw_next() search, we will either
+		 * have a presumed-free UID or we will be at UID_MAX + 1.
+		 */
+		if (highest_found > uid_max) {
+			/*
+			 * In this case, a UID is in use at UID_MAX.
+			 *
+			 * We will reset the search to UID_MIN and proceed up
+			 * through all the UIDs (skipping those we detected with
+			 * used_uids) for a free one. It is a known issue that
+			 * this may result in reusing a previously-deleted UID,
+			 * so administrators should be instructed to use this
+			 * auto-detection with care (and prefer to assign UIDs
+			 * explicitly).
+			 */
+			highest_found = uid_min;
 		}
-	}
 
-	/*
-	 * If a user (resp. system user) with UID equal to UID_MAX (resp.
-	 * UID_MIN) exists, the above algorithm will give us UID_MAX+1
-	 * (resp. UID_MIN-1) even if not unique. Search for the first free
-	 * UID starting with UID_MIN (resp. UID_MAX).
-	 */
-	if (sys_user) {
-		if (user_id < uid_min) {
-			for (user_id = uid_max; user_id >= uid_min; user_id--) {
-				if (false == used_uids[user_id]) {
-					break;
-				}
-			}
-			if (user_id < uid_min ) {
-				fprintf (stderr,
-				         _("%s: Can't get unique system UID (no more available UIDs)\n"),
-				         Prog);
-				SYSLOG ((LOG_WARN,
-				         "no more available UID on the system"));
+		/* Search through all of the IDs in the range */
+		for (id = highest_found; id <= uid_max; id++) {
+			result = check_uid (id, uid_min, uid_max, used_uids);
+			if (result == 0) {
+				/* This UID is available. Return it. */
+				*uid = id;
 				free (used_uids);
-				return -1;
+				return 0;
+			} else if (result == EEXIST) {
+				/* This UID is in use, we'll continue to the next */
+			} else {
+				/*
+				 * An unexpected error occurred.
+				 *
+				 * Only report it the first time to avoid spamming
+				 * the logs
+				 *
+				 */
+				if (!nospam) {
+					fprintf (stderr,
+						_("%s: Can't get unique UID (%s). "
+						  "Suppressing additional messages.\n"),
+						Prog, strerror (result));
+					SYSLOG ((LOG_ERR,
+						"Error checking available UIDs: %s",
+						strerror (result)));
+					nospam = 1;
+				}
+				/*
+				 * We will continue anyway. Hopefully a later UID
+				 * will work properly.
+				 */
 			}
 		}
-	} else {
-		if (user_id > uid_max) {
-			for (user_id = uid_min; user_id <= uid_max; user_id++) {
-				if (false == used_uids[user_id]) {
-					break;
+
+		/*
+		 * If we get all the way through the loop, try again from UID_MIN,
+		 * unless that was where we previously started. (NOTE: the worst-case
+		 * scenario here is that we will run through (UID_MAX - UID_MIN - 1)
+		 * cycles *again* if we fall into this case with highest_found as
+		 * UID_MIN + 1, all users in the range in use and maintained by
+		 * network services such as LDAP.)
+		 */
+		if (highest_found != uid_min) {
+			for (id = uid_min; id <= uid_max; id++) {
+				result = check_uid (id, uid_min, uid_max, used_uids);
+				if (result == 0) {
+					/* This UID is available. Return it. */
+					*uid = id;
+					free (used_uids);
+					return 0;
+				} else if (result == EEXIST) {
+					/* This UID is in use, we'll continue to the next */
+				} else {
+					/*
+					 * An unexpected error occurred.
+					 *
+					 * Only report it the first time to avoid spamming
+					 * the logs
+					 *
+					 */
+					if (!nospam) {
+						fprintf (stderr,
+							_("%s: Can't get unique UID (%s). "
+							  "Suppressing additional messages.\n"),
+							Prog, strerror (result));
+						SYSLOG ((LOG_ERR,
+							"Error checking available UIDs: %s",
+							strerror (result)));
+						nospam = 1;
+					}
+					/*
+					 * We will continue anyway. Hopefully a later UID
+					 * will work properly.
+					 */
 				}
 			}
-			if (user_id > uid_max) {
-				fprintf (stderr,
-				         _("%s: Can't get unique UID (no more available UIDs)\n"),
-				         Prog);
-				SYSLOG ((LOG_WARN, "no more available UID on the system"));
-				free (used_uids);
-				return -1;
-			}
 		}
 	}
 
+	/* The code reached here and found no available IDs in the range */
+	fprintf (stderr,
+		_("%s: Can't get unique UID (no more available UIDs)\n"),
+		Prog);
+	SYSLOG ((LOG_WARN, "no more available UIDs on the system"));
 	free (used_uids);
-	*uid = user_id;
-	return 0;
+	return -1;
 }