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authorDavid Howells <dhowells@redhat.com>2019-08-20 03:17:40 +0300
committerJames Morris <jmorris@namei.org>2019-08-20 07:54:15 +0300
commit49fcf732bdae0550721ef73af7c45109ce26b2a9 (patch)
treecdf90d95cc5fb01413ac3c83f51796c1c3a0cdec
parent000d388ed3bbed745f366ce71b2bb7c2ee70f449 (diff)
downloadlinux-49fcf732bdae0550721ef73af7c45109ce26b2a9.tar.xz
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>
-rw-r--r--include/linux/security.h1
-rw-r--r--init/Kconfig5
-rw-r--r--kernel/module.c37
-rw-r--r--security/lockdown/Kconfig1
-rw-r--r--security/lockdown/lockdown.c1
5 files changed, 38 insertions, 7 deletions
diff --git a/include/linux/security.h b/include/linux/security.h
index 74787335d9ce..9e8abb60a99f 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -103,6 +103,7 @@ enum lsm_event {
*/
enum lockdown_reason {
LOCKDOWN_NONE,
+ LOCKDOWN_MODULE_SIGNATURE,
LOCKDOWN_INTEGRITY_MAX,
LOCKDOWN_CONFIDENTIALITY_MAX,
};
diff --git a/init/Kconfig b/init/Kconfig
index 0e2344389501..e6069368f278 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -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
diff --git a/kernel/module.c b/kernel/module.c
index 80c7c09584cf..2206c08a5e10 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -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;
- }
- /* Not having a signature is only an error if we're strict. */
- if (err == -ENOKEY && !is_module_sig_enforced())
- err = 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 err;
+ 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;
+ }
}
#else /* !CONFIG_MODULE_SIG */
static int module_sig_check(struct load_info *info, int flags)
diff --git a/security/lockdown/Kconfig b/security/lockdown/Kconfig
index 7a1d213227a4..e84ddf484010 100644
--- a/security/lockdown/Kconfig
+++ b/security/lockdown/Kconfig
@@ -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.
diff --git a/security/lockdown/lockdown.c b/security/lockdown/lockdown.c
index 7172ad75496b..d8e42125a5dd 100644
--- a/security/lockdown/lockdown.c
+++ b/security/lockdown/lockdown.c
@@ -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",
};