Add configure check for vfork(2) and fall back to fork(2) if missing.

config.h.in

@@ -1021,6 +1021,9 @@
 /* Define to 1 if you have the `va_copy' function. */
 #undef HAVE_VA_COPY
 
+/* Define to 1 if you have the `vfork' function. */
+#undef HAVE_VFORK
+
 /* Define to 1 if you have the `vsnprintf' function. */
 #undef HAVE_VSNPRINTF
 

configure

@@ -3261,6 +3261,7 @@ as_fn_append ac_func_c_list " faccessat HAVE_FACCESSAT"
 as_fn_append ac_func_c_list " wordexp HAVE_WORDEXP"
 as_fn_append ac_func_c_list " getauxval HAVE_GETAUXVAL"
 as_fn_append ac_func_c_list " strtoull HAVE_STRTOULL"
+as_fn_append ac_func_c_list " vfork HAVE_VFORK"
 as_fn_append ac_func_c_list " seteuid HAVE_SETEUID"
 
 # Auxiliary files required by this configure script.
@@ -21259,6 +21260,7 @@ done
 
 
 
+
   for ac_func in execvpe
 do :
   ac_fn_c_check_func "$LINENO" "execvpe" "ac_cv_func_execvpe"

configure.ac

@@ -2605,7 +2605,7 @@ dnl Function checks
 dnl
 AC_FUNC_GETGROUPS
 AC_FUNC_FSEEKO
-AC_CHECK_FUNCS_ONCE([fexecve fmemopen killpg nl_langinfo faccessat wordexp getauxval strtoull])
+AC_CHECK_FUNCS_ONCE([fexecve fmemopen killpg nl_langinfo faccessat wordexp getauxval strtoull vfork])
 AC_CHECK_FUNCS([execvpe], [SUDO_APPEND_INTERCEPT_EXP(execvpe)])
 AC_CHECK_FUNCS([pread], [
     # pread/pwrite on 32-bit HP-UX 11.x may not support large files

src/sudo_intercept.c

@@ -52,6 +52,10 @@
 #include "sudo_util.h"
 #include "pathnames.h"
 
+#ifndef HAVE_VFORK
+# define vfork fork
+#endif
+
 /* execl flavors */
 #define SUDO_EXECL	0x0
 #define SUDO_EXECLE	0x1