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 7478733..9e8abb6 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 0e23443..e606936 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 80c7c09..2206c08 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 7a1d213..e84ddf4 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 7172ad7..d8e4212 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",
 };