samples/check-exec: Add an enlighten "inc" interpreter and 28 tests

Add a very simple script interpreter called "inc" that can evaluate two
different commands (one per line):
- "?" to initialize a counter from user's input;
- "+" to increment the counter (which is set to 0 by default).

It is enlighten to only interpret executable files according to
AT_EXECVE_CHECK and the related securebits:

  # Executing a script with RESTRICT_FILE is only allowed if the script
  # is executable:
  ./set-exec -f -- ./inc script-exec.inc # Allowed
  ./set-exec -f -- ./inc script-noexec.inc # Denied

  # Executing stdin with DENY_INTERACTIVE is only allowed if stdin is an
  # executable regular file:
  ./set-exec -i -- ./inc -i < script-exec.inc # Allowed
  ./set-exec -i -- ./inc -i < script-noexec.inc # Denied

  # However, a pipe is not executable and it is then denied:
  cat script-noexec.inc | ./set-exec -i -- ./inc -i # Denied

  # Executing raw data (e.g. command argument) with DENY_INTERACTIVE is
  # always denied.
  ./set-exec -i -- ./inc -c "+" # Denied
  ./inc -c "$(<script-ask.inc)" # Allowed

  # To directly execute a script, we can update $PATH (used by `env`):
  PATH="${PATH}:." ./script-exec.inc

  # To execute several commands passed as argument:

Add a complete test suite to check the script interpreter against all
possible execution cases:

  make TARGETS=exec kselftest-install
  ./tools/testing/selftests/kselftest_install/run_kselftest.sh

Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Kees Cook <keescook@chromium.org>
Cc: Paul Moore <paul@paul-moore.com>
Cc: Serge Hallyn <serge@hallyn.com>
Signed-off-by: Mickaël Salaün <mic@digikod.net>
Link: https://lore.kernel.org/r/20241212174223.389435-8-mic@digikod.net
Signed-off-by: Kees Cook <kees@kernel.org>

1 files changed, 12 insertions, 2 deletions

diff --git a/tools/testing/selftests/exec/Makefile b/tools/testing/selftests/exec/Makefile
index 8713d1c862ae..45a3cfc435cf 100644
--- a/tools/testing/selftests/exec/Makefile
+++ b/tools/testing/selftests/exec/Makefile
@@ -10,9 +10,9 @@ ALIGN_PIES        := $(patsubst %,load_address.%,$(ALIGNS))
 ALIGN_STATIC_PIES := $(patsubst %,load_address.static.%,$(ALIGNS))
 ALIGNMENT_TESTS   := $(ALIGN_PIES) $(ALIGN_STATIC_PIES)
 
-TEST_PROGS := binfmt_script.py
+TEST_PROGS := binfmt_script.py check-exec-tests.sh
 TEST_GEN_PROGS := execveat non-regular $(ALIGNMENT_TESTS)
-TEST_GEN_PROGS_EXTENDED := false
+TEST_GEN_PROGS_EXTENDED := false inc set-exec script-exec.inc script-noexec.inc
 TEST_GEN_FILES := execveat.symlink execveat.denatured script subdir
 # Makefile is a run-time dependency, since it's accessed by the execveat test
 TEST_FILES := Makefile
@@ -26,6 +26,8 @@ EXTRA_CLEAN := $(OUTPUT)/subdir.moved $(OUTPUT)/execveat.moved $(OUTPUT)/xxxxx*
 
 include ../lib.mk
 
+CHECK_EXEC_SAMPLES := $(top_srcdir)/samples/check-exec
+
 $(OUTPUT)/subdir:
 	mkdir -p $@
 $(OUTPUT)/script: Makefile
@@ -45,3 +47,11 @@ $(OUTPUT)/load_address.static.0x%: load_address.c
 		-fPIE -static-pie $< -o $@
 $(OUTPUT)/false: false.c
 	$(CC) $(CFLAGS) $(LDFLAGS) -static $< -o $@
+$(OUTPUT)/inc: $(CHECK_EXEC_SAMPLES)/inc.c
+	$(CC) $(CFLAGS) $(LDFLAGS) $< -o $@
+$(OUTPUT)/set-exec: $(CHECK_EXEC_SAMPLES)/set-exec.c
+	$(CC) $(CFLAGS) $(LDFLAGS) $< -o $@
+$(OUTPUT)/script-exec.inc: $(CHECK_EXEC_SAMPLES)/script-exec.inc
+	cp $< $@
+$(OUTPUT)/script-noexec.inc: $(CHECK_EXEC_SAMPLES)/script-noexec.inc
+	cp $< $@