dm verity: Add support for signature verification with 2nd keyring

Add a new configuration DM_VERITY_VERIFY_ROOTHASH_SIG_SECONDARY_KEYRING
to enable dm-verity signatures to be verified against the secondary
trusted keyring.  Instead of relying on the builtin trusted keyring
(with hard-coded certificates), the second trusted keyring can include
certificate authorities from the builtin trusted keyring and child
certificates loaded at run time.  Using the secondary trusted keyring
enables to use dm-verity disks (e.g. loop devices) signed by keys which
did not exist at kernel build time, leveraging the certificate chain of
trust model.  In practice, this makes it possible to update certificates
without kernel update and reboot, aligning with module and kernel
(kexec) signature verification which already use the secondary trusted
keyring.

Signed-off-by: Mickaël Salaün <mic@linux.microsoft.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

diff --git a/Documentation/admin-guide/device-mapper/verity.rst b/Documentation/admin-guide/device-mapper/verity.rst
index 66f71f0dab1b36ec9d2e22e8fbde66603864e4bd..b088a647acb78fef2146f187e62f9df126220b55 100644 (file)
--- a/Documentation/admin-guide/device-mapper/verity.rst
+++ b/Documentation/admin-guide/device-mapper/verity.rst
@@ -134,7 +134,12 @@ root_hash_sig_key_desc <key_description>
     the pkcs7 signature of the roothash. The pkcs7 signature is used to validate
     the root hash during the creation of the device mapper block device.
     Verification of roothash depends on the config DM_VERITY_VERIFY_ROOTHASH_SIG
-    being set in the kernel.
+    being set in the kernel.  The signatures are checked against the builtin
+    trusted keyring by default, or the secondary trusted keyring if
+    DM_VERITY_VERIFY_ROOTHASH_SIG_SECONDARY_KEYRING is set.  The secondary
+    trusted keyring includes by default the builtin trusted keyring, and it can
+    also gain new certificates at run time if they are signed by a certificate
+    already in the secondary trusted keyring.
 
 Theory of operation
 ===================

diff --git a/drivers/md/Kconfig b/drivers/md/Kconfig
index 30ba3573626c2f61d25d47c48433492b028882e3..1d68935e45efb9655752a24af6849a6e33f31d56 100644 (file)
--- a/drivers/md/Kconfig
+++ b/drivers/md/Kconfig
@@ -530,11 +530,22 @@ config DM_VERITY_VERIFY_ROOTHASH_SIG
        bool "Verity data device root hash signature verification support"
        depends on DM_VERITY
        select SYSTEM_DATA_VERIFICATION
-         help
+       help
          Add ability for dm-verity device to be validated if the
          pre-generated tree of cryptographic checksums passed has a pkcs#7
          signature file that can validate the roothash of the tree.
 
+         By default, rely on the builtin trusted keyring.
+
+         If unsure, say N.
+
+config DM_VERITY_VERIFY_ROOTHASH_SIG_SECONDARY_KEYRING
+       bool "Verity data device root hash signature verification with secondary keyring"
+       depends on DM_VERITY_VERIFY_ROOTHASH_SIG
+       depends on SECONDARY_TRUSTED_KEYRING
+       help
+         Rely on the secondary trusted keyring to verify dm-verity signatures.
+
          If unsure, say N.
 
 config DM_VERITY_FEC

diff --git a/drivers/md/dm-verity-verify-sig.c b/drivers/md/dm-verity-verify-sig.c
index 614e43db93aa835245324b6c88a1092cda10f6a7..29385dc470d5d9509c41a127ea0e4478017a6cac 100644 (file)
--- a/drivers/md/dm-verity-verify-sig.c
+++ b/drivers/md/dm-verity-verify-sig.c
@@ -119,8 +119,13 @@ int verity_verify_root_hash(const void *root_hash, size_t root_hash_len,
        }
 
        ret = verify_pkcs7_signature(root_hash, root_hash_len, sig_data,
-                               sig_len, NULL, VERIFYING_UNSPECIFIED_SIGNATURE,
-                               NULL, NULL);
+                               sig_len,
+#ifdef CONFIG_DM_VERITY_VERIFY_ROOTHASH_SIG_SECONDARY_KEYRING
+                               VERIFY_USE_SECONDARY_KEYRING,
+#else
+                               NULL,
+#endif
+                               VERIFYING_UNSPECIFIED_SIGNATURE, NULL, NULL);
 
        return ret;
 }