lockdown: Enforce module signatures if the kernel is locked down

If the kernel is locked down, require that all modules have valid
signatures that we can verify.

I have adjusted the errors generated:

 (1) If there's no signature (ENODATA) or we can't check it (ENOPKG,
     ENOKEY), then:

     (a) If signatures are enforced then EKEYREJECTED is returned.

     (b) If there's no signature or we can't check it, but the kernel is
	 locked down then EPERM is returned (this is then consistent with
	 other lockdown cases).

 (2) If the signature is unparseable (EBADMSG, EINVAL), the signature fails
     the check (EKEYREJECTED) or a system error occurs (eg. ENOMEM), we
     return the error we got.

Note that the X.509 code doesn't check for key expiry as the RTC might not
be valid or might not have been transferred to the kernel's clock yet.

 [Modified by Matthew Garrett to remove the IMA integration. This will
  be replaced with integration with the IMA architecture policy
  patchset.]

Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Matthew Garrett <matthewgarrett@google.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Cc: Jessica Yu <jeyu@kernel.org>
Signed-off-by: James Morris <jmorris@namei.org>
This commit is contained in:
David Howells 2019-08-19 17:17:40 -07:00 committed by James Morris
parent 000d388ed3
commit 49fcf732bd
5 changed files with 39 additions and 8 deletions

View File

@ -103,6 +103,7 @@ enum lsm_event {
*/
enum lockdown_reason {
LOCKDOWN_NONE,
LOCKDOWN_MODULE_SIGNATURE,
LOCKDOWN_INTEGRITY_MAX,
LOCKDOWN_CONFIDENTIALITY_MAX,
};

View File

@ -1939,6 +1939,11 @@ config MODULE_SIG
kernel build dependency so that the signing tool can use its crypto
library.
You should enable this option if you wish to use either
CONFIG_SECURITY_LOCKDOWN_LSM or lockdown functionality imposed via
another LSM - otherwise unsigned modules will be loadable regardless
of the lockdown policy.
!!!WARNING!!! If you enable this option, you MUST make sure that the
module DOES NOT get stripped after being signed. This includes the
debuginfo strip done by some packagers (such as rpmbuild) and

View File

@ -2753,8 +2753,9 @@ static inline void kmemleak_load_module(const struct module *mod,
#ifdef CONFIG_MODULE_SIG
static int module_sig_check(struct load_info *info, int flags)
{
int err = -ENOKEY;
int err = -ENODATA;
const unsigned long markerlen = sizeof(MODULE_SIG_STRING) - 1;
const char *reason;
const void *mod = info->hdr;
/*
@ -2769,16 +2770,38 @@ static int module_sig_check(struct load_info *info, int flags)
err = mod_verify_sig(mod, info);
}
if (!err) {
switch (err) {
case 0:
info->sig_ok = true;
return 0;
/* We don't permit modules to be loaded into trusted kernels
* without a valid signature on them, but if we're not
* enforcing, certain errors are non-fatal.
*/
case -ENODATA:
reason = "Loading of unsigned module";
goto decide;
case -ENOPKG:
reason = "Loading of module with unsupported crypto";
goto decide;
case -ENOKEY:
reason = "Loading of module with unavailable key";
decide:
if (is_module_sig_enforced()) {
pr_notice("%s is rejected\n", reason);
return -EKEYREJECTED;
}
return security_locked_down(LOCKDOWN_MODULE_SIGNATURE);
/* All other errors are fatal, including nomem, unparseable
* signatures and signature check failures - even if signatures
* aren't required.
*/
default:
return err;
}
/* Not having a signature is only an error if we're strict. */
if (err == -ENOKEY && !is_module_sig_enforced())
err = 0;
return err;
}
#else /* !CONFIG_MODULE_SIG */
static int module_sig_check(struct load_info *info, int flags)

View File

@ -1,6 +1,7 @@
config SECURITY_LOCKDOWN_LSM
bool "Basic module for enforcing kernel lockdown"
depends on SECURITY
select MODULE_SIG if MODULES
help
Build support for an LSM that enforces a coarse kernel lockdown
behaviour.

View File

@ -18,6 +18,7 @@ static enum lockdown_reason kernel_locked_down;
static char *lockdown_reasons[LOCKDOWN_CONFIDENTIALITY_MAX+1] = {
[LOCKDOWN_NONE] = "none",
[LOCKDOWN_MODULE_SIGNATURE] = "unsigned module loading",
[LOCKDOWN_INTEGRITY_MAX] = "integrity",
[LOCKDOWN_CONFIDENTIALITY_MAX] = "confidentiality",
};