When a dynamic NSS module is built and linked against a thread

library, it may pull in that thread library at run time.  If the
process started out single-threaded, this could cause attempts to
release locks that do not exist.  Guard against this possibility by
checking __isthreaded before invoking thread primitives.

A similar problem remains if the process is linked against one thread
library, but the NSS module is linked against another.  This can only
be avoided by careful design of the NSS module.

Submitted by:	Sean McNeil <sean@mcneil.com> (mostly; bugs are mine)

lib/libc/include/nss_tls.h

@@ -75,6 +75,6 @@ name##_getstate(struct name##_state **p)			\
 	return (rv);						\
 }								\
 /* allow the macro invocation to end with a semicolon */	\
-typedef int _##name##_bmVjdGFy
+struct _clashproof_bmVjdGFy
 
 #endif /* _NSS_TLS_H_ */

lib/libc/net/nsdispatch.c

@@ -316,9 +316,11 @@ nss_configure(void)
 	static pthread_mutex_t conf_lock = PTHREAD_MUTEX_INITIALIZER;
 	static time_t	 confmod;
 	struct stat	 statbuf;
-	int		 result;
+	int		 result, isthreaded;
 	const char	*path;
 
+	result = 0;
+	isthreaded = __isthreaded;
 #if defined(_NSS_DEBUG) && defined(_NSS_SHOOT_FOOT)
 	/* NOTE WELL:  THIS IS A SECURITY HOLE. This must only be built
 	 * for debugging purposes and MUST NEVER be used in production.
@@ -331,16 +333,20 @@ nss_configure(void)
 		return (0);
 	if (statbuf.st_mtime <= confmod)
 		return (0);
-	result = _pthread_mutex_trylock(&conf_lock);
-	if (result != 0)
-		return (0);
-	(void)_pthread_rwlock_unlock(&nss_lock);
-	result = _pthread_rwlock_wrlock(&nss_lock);
-	if (result != 0)
-		goto fin2;
+	if (isthreaded) {
+	    result = _pthread_mutex_trylock(&conf_lock);
+	    if (result != 0)
+		    return (0);
+	    (void)_pthread_rwlock_unlock(&nss_lock);
+	    result = _pthread_rwlock_wrlock(&nss_lock);
+	    if (result != 0)
+		    goto fin2;
+	}
 	_nsyyin = fopen(path, "r");
-	if (_nsyyin == NULL)
+	if (_nsyyin == NULL) {
+		result = errno;
 		goto fin;
+	}
 	VECTOR_FREE(_nsmap, &_nsmapsize, sizeof(*_nsmap),
 	    (vector_free_elem)ns_dbt_free);
 	VECTOR_FREE(_nsmod, &_nsmodsize, sizeof(*_nsmod),
@@ -353,10 +359,14 @@ nss_configure(void)
 		(void)atexit(nss_atexit);
 	confmod = statbuf.st_mtime;
 fin:
-	(void)_pthread_rwlock_unlock(&nss_lock);
-	result = _pthread_rwlock_rdlock(&nss_lock);
+	if (isthreaded) {
+	    (void)_pthread_rwlock_unlock(&nss_lock);
+	    if (result == 0)
+		    result = _pthread_rwlock_rdlock(&nss_lock);
+	}
 fin2:
-	(void)_pthread_mutex_unlock(&conf_lock);
+	if (isthreaded)
+		(void)_pthread_mutex_unlock(&conf_lock);
 	return (result);
 }
 
@@ -510,12 +520,17 @@ ns_mod_free(ns_mod *mod)
 static void
 nss_atexit(void)
 {
-	(void)_pthread_rwlock_wrlock(&nss_lock);
+	int isthreaded;
+
+	isthreaded = __isthreaded;
+	if (isthreaded)
+		(void)_pthread_rwlock_wrlock(&nss_lock);
 	VECTOR_FREE(_nsmap, &_nsmapsize, sizeof(*_nsmap),
 	    (vector_free_elem)ns_dbt_free);
 	VECTOR_FREE(_nsmod, &_nsmodsize, sizeof(*_nsmod),
 	    (vector_free_elem)ns_mod_free);
-	(void)_pthread_rwlock_unlock(&nss_lock);
+	if (isthreaded)
+		(void)_pthread_rwlock_unlock(&nss_lock);
 }
 
 
@@ -568,13 +583,16 @@ _nsdispatch(void *retval, const ns_dtab disp_tab[], const char *database,
 	const ns_src	*srclist;
 	nss_method	 method;
 	void		*mdata;
-	int		 serrno, i, result, srclistsize;
+	int		 isthreaded, serrno, i, result, srclistsize;
 
+	isthreaded = __isthreaded;
 	serrno = errno;
-	result = _pthread_rwlock_rdlock(&nss_lock);
-	if (result != 0) {
-		result = NS_UNAVAIL;
-		goto fin;
+	if (isthreaded) {
+		result = _pthread_rwlock_rdlock(&nss_lock);
+		if (result != 0) {
+			result = NS_UNAVAIL;
+			goto fin;
+		}
 	}
 	result = nss_configure();
 	if (result != 0) {
@@ -604,7 +622,8 @@ _nsdispatch(void *retval, const ns_dtab disp_tab[], const char *database,
 				break;
 		}
 	}
-	(void)_pthread_rwlock_unlock(&nss_lock);
+	if (isthreaded)
+		(void)_pthread_rwlock_unlock(&nss_lock);
 fin:
 	errno = serrno;
 	return (result);

lib/libc/net/nss_compat.c

@@ -41,6 +41,7 @@ __FBSDID("$FreeBSD$");
 #include <pthread.h>
 #include <pthread_np.h>
 #include "un-namespace.h"
+#include "libc_private.h"
 
 
 struct group;
@@ -60,7 +61,7 @@ static pthread_once_t	 _term_once_##x = PTHREAD_ONCE_INIT
 
 #define SET_TERMINATOR(x, y)						\
 do {									\
-	if (_pthread_main_np())						\
+	if (!__isthreaded || _pthread_main_np())			\
 		_term_main_##x = (y);					\
 	else {								\
 		(void)_pthread_once(&_term_once_##x, _term_create_##x);	\
@@ -69,7 +70,7 @@ do {									\
 } while (0)
 
 #define CHECK_TERMINATOR(x)					\
-(_pthread_main_np() ?						\
+(!__isthreaded || _pthread_main_np() ?				\
     (_term_main_##x) :						\
     ((void)_pthread_once(&_term_once_##x, _term_create_##x),	\
     _pthread_getspecific(_term_key_##x)))