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authorSascha Hauer <s.hauer@pengutronix.de>2019-05-14 11:33:22 +0300
committerRichard Weinberger <richard@nod.at>2019-07-08 20:43:52 +0300
commit817aa094842dfc3a6b98c9582d4a647827f66201 (patch)
tree68919bfade27218cdb9e66c8bcaa2f2aa32b685e /fs/ubifs/auth.c
parent8ba0a2ab84b23b541a5d2ef25d759c94880e7457 (diff)
downloadlinux-817aa094842dfc3a6b98c9582d4a647827f66201.tar.xz
ubifs: support offline signed images
HMACs can only be generated on the system the UBIFS image is running on. To support offline signed images we add a PKCS#7 signature to the UBIFS image which can be created by mkfs.ubifs. Both the master node and the superblock need to be authenticated, during normal runtime both are protected with HMACs. For offline signature support however only a single signature is desired. We add a signature covering the superblock node directly behind it. To protect the master node a hash of the master node is added to the superblock which is used when the master node doesn't contain a HMAC. Transition to a read/write filesystem is also supported. During transition first the master node is rewritten with a HMAC (implicitly, it is written anyway as the FS is marked dirty). Afterwards the superblock is rewritten with a HMAC. Once after the image has been mounted read/write it is HMAC only, the signature is no longer required or even present on the filesystem. In an offline signed image the master node is authenticated by the superblock. In a transition to r/w we have to make sure that the master node is rewritten before the superblock node. In this case the master node gets a HMAC and its authenticity no longer depends on the superblock node. There are some cases in which the current code first writes the superblock node though, so with this patch writing of the superblock node is delayed until the master node is written. Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de> Signed-off-by: Richard Weinberger <richard@nod.at>
Diffstat (limited to 'fs/ubifs/auth.c')
-rw-r--r--fs/ubifs/auth.c86
1 files changed, 86 insertions, 0 deletions
diff --git a/fs/ubifs/auth.c b/fs/ubifs/auth.c
index 60f43b93d06e..d9af2de9084a 100644
--- a/fs/ubifs/auth.c
+++ b/fs/ubifs/auth.c
@@ -10,10 +10,12 @@
*/
#include <linux/crypto.h>
+#include <linux/verification.h>
#include <crypto/hash.h>
#include <crypto/sha.h>
#include <crypto/algapi.h>
#include <keys/user-type.h>
+#include <keys/asymmetric-type.h>
#include "ubifs.h"
@@ -199,6 +201,77 @@ int __ubifs_node_check_hash(const struct ubifs_info *c, const void *node,
}
/**
+ * ubifs_sb_verify_signature - verify the signature of a superblock
+ * @c: UBIFS file-system description object
+ * @sup: The superblock node
+ *
+ * To support offline signed images the superblock can be signed with a
+ * PKCS#7 signature. The signature is placed directly behind the superblock
+ * node in an ubifs_sig_node.
+ *
+ * Returns 0 when the signature can be successfully verified or a negative
+ * error code if not.
+ */
+int ubifs_sb_verify_signature(struct ubifs_info *c,
+ const struct ubifs_sb_node *sup)
+{
+ int err;
+ struct ubifs_scan_leb *sleb;
+ struct ubifs_scan_node *snod;
+ const struct ubifs_sig_node *signode;
+
+ sleb = ubifs_scan(c, UBIFS_SB_LNUM, UBIFS_SB_NODE_SZ, c->sbuf, 0);
+ if (IS_ERR(sleb)) {
+ err = PTR_ERR(sleb);
+ return err;
+ }
+
+ if (sleb->nodes_cnt == 0) {
+ ubifs_err(c, "Unable to find signature node");
+ err = -EINVAL;
+ goto out_destroy;
+ }
+
+ snod = list_first_entry(&sleb->nodes, struct ubifs_scan_node, list);
+
+ if (snod->type != UBIFS_SIG_NODE) {
+ ubifs_err(c, "Signature node is of wrong type");
+ err = -EINVAL;
+ goto out_destroy;
+ }
+
+ signode = snod->node;
+
+ if (le32_to_cpu(signode->len) > snod->len + sizeof(struct ubifs_sig_node)) {
+ ubifs_err(c, "invalid signature len %d", le32_to_cpu(signode->len));
+ err = -EINVAL;
+ goto out_destroy;
+ }
+
+ if (le32_to_cpu(signode->type) != UBIFS_SIGNATURE_TYPE_PKCS7) {
+ ubifs_err(c, "Signature type %d is not supported\n",
+ le32_to_cpu(signode->type));
+ err = -EINVAL;
+ goto out_destroy;
+ }
+
+ err = verify_pkcs7_signature(sup, sizeof(struct ubifs_sb_node),
+ signode->sig, le32_to_cpu(signode->len),
+ NULL, VERIFYING_UNSPECIFIED_SIGNATURE,
+ NULL, NULL);
+
+ if (err)
+ ubifs_err(c, "Failed to verify signature");
+ else
+ ubifs_msg(c, "Successfully verified super block signature");
+
+out_destroy:
+ ubifs_scan_destroy(sleb);
+
+ return err;
+}
+
+/**
* ubifs_init_authentication - initialize UBIFS authentication support
* @c: UBIFS file-system description object
*
@@ -478,3 +551,16 @@ int ubifs_hmac_wkm(struct ubifs_info *c, u8 *hmac)
return err;
return 0;
}
+
+/*
+ * ubifs_hmac_zero - test if a HMAC is zero
+ * @c: UBIFS file-system description object
+ * @hmac: the HMAC to test
+ *
+ * This function tests if a HMAC is zero and returns true if it is
+ * and false otherwise.
+ */
+bool ubifs_hmac_zero(struct ubifs_info *c, const u8 *hmac)
+{
+ return !memchr_inv(hmac, 0, c->hmac_desc_len);
+}