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>
