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>

diff --git a/include/linux/security.h b/include/linux/security.h
index 74787335d9ce12b60a4ce4ca68050ae8c8873569..9e8abb60a99ff8c737c3353568ca22b01f39b236 100644 (file)
--- 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 0e2344389501ec0f9516951f62cc5332b87b5045..e6069368f2781ad79d21328ab5662076ca557cca 100644 (file)
--- 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 80c7c09584cf97d4eaa16549b42827d7ea6ced46..2206c08a5e108a0ab544de58de49bce91c4956d6 100644 (file)
--- 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 7a1d213227a4b8dace0f64c747d73dd1524e7a3e..e84ddf48401010bcc0829a32db58e6f12bfdedcb 100644 (file)
--- 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 7172ad75496b8c0584de3aaf8484c4627e72a296..d8e42125a5ddb7c67640f24329d65ba210d57475 100644 (file)
--- 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",
 };