register the atfork handler from arc4random

From kettenis@

People have suggested using pthread_atfork(3) before, but discarded
the idea because it involves linking with -lpthread, which has other
undesirable consequences.  However:

* Most systems actually have pthread_atfork(3) in libc.  I verified
  this on OS X and Solaris.  I believe this is the case on Linux
  systems that use musl as well.

* On Linux systems that use glibc, this isn't the case.  However,
  those systems have __register_atfork(3), which is fully documented
  in the "Linux Standard Base Core Specification".

ok kettenis@ deraadt@ beck@

1 files changed, 8 insertions, 0 deletions

diff --git a/crypto/compat/thread_private.h b/crypto/compat/thread_private.h
index 3286a7c..c5b0daf 100644
--- a/crypto/compat/thread_private.h
+++ b/crypto/compat/thread_private.h
@@ -4,3 +4,11 @@ static pthread_mutex_t arc4random_mtx = PTHREAD_MUTEX_INITIALIZER;
 
 #define _ARC4_LOCK()   pthread_mutex_lock(&arc4random_mtx)
 #define _ARC4_UNLOCK() pthread_mutex_unlock(&arc4random_mtx)
+
+#ifdef __GLIBC__
+extern void *__dso_handle;
+extern int __register_atfork(void (*)(void), void(*)(void), void (*)(void), void *);
+#define _ARC4_ATFORK(f) __register_atfork(NULL, NULL, (f), __dso_handle)
+#else
+#define _ARC4_ATFORK(f) pthread_atfork(NULL, NULL, (f))
+#endif