pthread_atfork handlers not removed during dlclose

Invoke pthread_atfork handler cleanup when removing the associated DSO...

If a program loads a DSO (dlopen) that sets up a pthread_atfork handler(s), and
then subsequently closes the DSO, the handler(s) are left in place.  If fork()
is subsequently called, the handlers are invoked even though the DSO has been
removed causing crashes or unpredictable code execution.  This is because the
code in __cxa_finalize(atexit.c)to invoke the unregister_atfork() routine is
ifdef'd out with the comment that it hasn't been "looked into this yet...".

Refs.:
 http://bugs.busybox.net/show_bug.cgi?id=8211
 http://sourceware.org/bugzilla/show_bug.cgi?id=13502

Add test-case, enable cleanup for NPTL only.

Signed-off-by: John Ata <john.ata@baesystems.com>
Signed-off-by: Leonid Lisovskiy <lly.dev@gmail.com>

libc/stdlib/_atexit.c

@@ -43,6 +43,9 @@
 #include <stdio.h>
 #include <errno.h>
 #include <atomic.h>
+#if defined __UCLIBC_HAS_THREADS__ && defined __UCLIBC_HAS_THREADS_NATIVE__
+# include <fork.h>
+#endif
 
 #include <bits/uClibc_mutex.h>
 __UCLIBC_MUTEX_EXTERN(__atexit_lock) attribute_hidden;
@@ -208,17 +211,15 @@ void __cxa_finalize(void *dso_handle)
         }
     }
 
-#if 0 /* haven't looked into this yet... */
     /*
      * Remove the registered fork handlers. We do not have to
      * unregister anything if the program is going to terminate anyway.
      */
 #ifdef UNREGISTER_ATFORK
-    if (d != NULL) {
+    if (dso_handle != NULL) {
-        UNREGISTER_ATFORK(d);
+        UNREGISTER_ATFORK(dso_handle);
     }
 #endif
-#endif
 }
 #endif
 

test/nptl/Makefile.in

@@ -42,7 +42,8 @@ TESTS := tst-align tst-align2 tst-atfork1 tst-attr1 tst-attr2 tst-attr3	\
 	tst-oddstacklimit tst-oncex3 tst-oncex4 tst-rwlock2a  \
 	tst-basic7 tst-signal7 tst-vfork1x tst-vfork2x tst-sem10 tst-sem11 \
 	tst-sem12 tst-typesizes tst-initializers1-c89 tst-initializers1-c99 \
-	tst-initializers1-gnu89 tst-initializers1-gnu99
+	tst-initializers1-gnu89 tst-initializers1-gnu99 \
+	tst-atfork2
 
 #
 # These are for the RT library and POSIX timers.
@@ -151,6 +152,8 @@ CFLAGS_tst-initializers1-gnu99 = $(CFLAGS-tst-initializers1) -std=gnu99
 
 EXTRA_LDFLAGS = $(if $(findstring -lpthread,$(LDFLAGS_$@)),,-lpthread)
 
+LDFLAGS_tst-atfork2 := -ldl
+LDFLAGS_libatfork.so := -shared -static-libgcc -lpthread
 LDFLAGS_tst-cleanup4 := tst-cleanup4aux.o
 LDFLAGS_tst-cleanupx4 := tst-cleanup4aux.o
 LDFLAGS_tst-clock2 := -lrt
@@ -207,6 +210,9 @@ tst-tls5: tst-tls5mod.so
 tst-cleanupx4 : tst-cleanup4aux.o
 tst-fini1: tst-fini1mod.so
 
+tst-atfork2: libatfork.so
+tst-atfork2_glibc: libatfork.so.glibc
+
 OPTS_tst-cancel7 = -c ./tst-cancel7
 OPTS_tst-mqueue7 = -- ./tst-mqueue7
 OPTS_tst-exec4 = ./tst-exec4

test/nptl/libatfork.c

@@ -0,0 +1,27 @@
+#include <stdio.h>
+#include <pthread.h>
+
+static void atfork_prepare(void)
+{
+    /*  nothing to do  */
+}
+
+static void atfork_parent(void)
+{
+    /*  nothing to do  */
+}
+
+static void atfork_child(void)
+{
+    /*  nothing to do  */
+}
+
+static __attribute__((constructor)) void init(void)
+{
+    pthread_atfork(atfork_prepare, atfork_parent, atfork_child);
+}
+
+static __attribute__((destructor)) void done(void)
+{
+    /*  nothing to do  */
+}

test/nptl/tst-atfork2.c

@@ -0,0 +1,24 @@
+#include <stdio.h>
+#include <unistd.h>
+#include <dlfcn.h>
+
+int main(int argc, char *argv[])
+{
+    void *h;
+    pid_t pid;
+
+    h = dlopen("libatfork.so", RTLD_NOW);
+    if (!h)
+    {
+        printf("Failed to open libatfork.so\n");
+        return 1;
+    }
+    dlclose(h);
+
+    if ((pid = fork()) < 0) {
+	printf("Fork failed\n");
+        return 1;
+    }
+
+    return 0;
+}