support: Add capability to fork an sgid child

Add a new function support_capture_subprogram_self_sgid that spawns an
sgid child of the running program with its own image and returns the
exit code of the child process.  This functionality is used by at
least three tests in the testsuite at the moment, so it makes sense to
consolidate.

There is also a new function support_subprogram_wait which should
provide simple system() like functionality that does not set up file
actions.  This is useful in cases where only the return code of the
spawned subprocess is interesting.

This patch also ports tst-secure-getenv to this new function.  A
subsequent patch will port other tests.  This also brings an important
change to tst-secure-getenv behaviour.  Now instead of succeeding, the
test fails as UNSUPPORTED if it is unable to spawn a setgid child,
which is how it should have been in the first place.
Reviewed-by: Carlos O'Donell <carlos@redhat.com>

1 files changed, 6 insertions, 0 deletions

diff --git a/support/capture_subprocess.h b/support/capture_subprocess.h
index 8969d4a99a..4be430f099 100644
--- a/support/capture_subprocess.h
+++ b/support/capture_subprocess.h
@@ -41,6 +41,12 @@ struct support_capture_subprocess support_capture_subprocess
 struct support_capture_subprocess support_capture_subprogram
   (const char *file, char *const argv[]);
 
+/* Copy the running program into a setgid binary and run it with CHILD_ID
+   argument.  If execution is successful, return the exit status of the child
+   program, otherwise return a non-zero failure exit code.  */
+int support_capture_subprogram_self_sgid
+  (char *child_id);
+
 /* Deallocate the subprocess data captured by
    support_capture_subprocess.  */
 void support_capture_subprocess_free (struct support_capture_subprocess *);