Add a helper binary to create a basic Secure Computing filter.scratch/seccomp-helper-binary

The binary uses the 'seccomp' helper library.  The library isn't
needed to load the generated Secure Computing filter.

* configure.ac: Check for 'seccomp' header and library.

* lib-src/seccomp-filter.c: New helper binary to generate a generic
Secure Computing filter for GNU/Linux.

* lib-src/Makefile.in (DONT_INSTALL): Add 'seccomp-filter' helper
binary if possible.
(all): Add Secure Computing filter file if possible.
(seccomp-filter$(EXEEXT)): Compile helper binary.
(seccomp-filter.bpf seccomp-filter.pfc): Generate filter files.

* test/src/emacs-tests.el (emacs-tests/seccomp/allows-stdout)
(emacs-tests/seccomp/forbids-subprocess): New unit tests.

* test/Makefile.in (src/emacs-tests.log): Add dependency on the helper
binary.

1 files changed, 5 insertions, 0 deletions

diff --git a/configure.ac b/configure.ac
index 684788a4d33..0c4772a2b96 100644
--- a/configure.ac
+++ b/configure.ac
@@ -4181,6 +4181,11 @@ AC_SUBST([LIBS_MAIL])
 
 AC_CHECK_HEADERS([linux/seccomp.h], [HAVE_SECCOMP=yes])
 
+LIBSECCOMP=
+AC_CHECK_HEADER([seccomp.h],
+  [AC_CHECK_LIB([seccomp], [seccomp_init], [LIBSECCOMP=-lseccomp])])
+AC_SUBST([LIBSECCOMP])
+
 OLD_LIBS=$LIBS
 LIBS="$LIB_PTHREAD $LIB_MATH $LIBS"
 AC_CHECK_FUNCS(accept4 fchdir gethostname \