3 files changed, 30 insertions, 0 deletions

diff --git a/configure.ac b/configure.ac
index 70e72be77..d2fb4469c 100644
--- a/configure.ac
+++ b/configure.ac
@@ -2059,6 +2059,16 @@ AC_CHECK_FUNCS([realpath], [
         )
 ])
 
+AC_MSG_CHECKING([for working fflush(NULL)])
+AC_RUN_IFELSE(
+        [AC_LANG_PROGRAM([[#include <stdio.h>]], [[fflush(NULL); exit(0);]])],
+        AC_MSG_RESULT([yes]),
+        [AC_MSG_RESULT([no])
+         AC_DEFINE([FFLUSH_NULL_BUG], [1],
+            [define if fflush(NULL) does not work])],
+        AC_MSG_WARN([cross compiling: assuming working])
+)
+
 dnl    Checks for time functions
 AC_CHECK_FUNCS([gettimeofday time])
 dnl    Checks for utmp functions
diff --git a/openbsd-compat/bsd-misc.c b/openbsd-compat/bsd-misc.c
index f7187daf8..3daf61071 100644
--- a/openbsd-compat/bsd-misc.c
+++ b/openbsd-compat/bsd-misc.c
@@ -308,3 +308,19 @@ getsid(pid_t pid)
 }
 #endif
 
+#ifdef FFLUSH_NULL_BUG
+#undef fflush
+int _ssh_compat_fflush(FILE *f)
+{
+        int r1, r2, r3;
+
+        if (f == NULL) {
+                r2 = fflush(stdout);
+                r3 = fflush(stderr);
+                if (r1 == -1 || r2 == -1 || r3 == -1)
+                        return -1;
+                return 0;
+        }
+        return fflush(f);
+}
+#endif
diff --git a/openbsd-compat/bsd-misc.h b/openbsd-compat/bsd-misc.h
index fb81e6c72..52ec52853 100644
--- a/openbsd-compat/bsd-misc.h
+++ b/openbsd-compat/bsd-misc.h
@@ -153,4 +153,8 @@ pid_t getsid(pid_t);
 int flock(int, int);
 #endif
 
+#ifdef FFLUSH_NULL_BUG
+# define fflush(x)      (_ssh_compat_fflush(x))
+#endif
+
 #endif /* _BSD_MISC_H */