1 files changed, 157 insertions, 0 deletions
diff --git a/fs/verity/signature.c b/fs/verity/signature.c
new file mode 100644
index 000000000000..c8b255232de5
--- /dev/null
+++ b/fs/verity/signature.c
@@ -0,0 +1,157 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * fs/verity/signature.c: verification of builtin signatures
+ *
+ * Copyright 2019 Google LLC
+ */
+
+#include "fsverity_private.h"
+
+#include <linux/cred.h>
+#include <linux/key.h>
+#include <linux/slab.h>
+#include <linux/verification.h>
+
+/*
+ * /proc/sys/fs/verity/require_signatures
+ * If 1, all verity files must have a valid builtin signature.
+ */
+static int fsverity_require_signatures;
+
+/*
+ * Keyring that contains the trusted X.509 certificates.
+ *
+ * Only root (kuid=0) can modify this.  Also, root may use
+ * keyctl_restrict_keyring() to prevent any more additions.
+ */
+static struct key *fsverity_keyring;
+
+/**
+ * fsverity_verify_signature() - check a verity file's signature
+ *
+ * If the file's fs-verity descriptor includes a signature of the file
+ * measurement, verify it against the certificates in the fs-verity keyring.
+ *
+ * Return: 0 on success (signature valid or not required); -errno on failure
+ */
+int fsverity_verify_signature(const struct fsverity_info *vi,
+			      const struct fsverity_descriptor *desc,
+			      size_t desc_size)
+{
+	const struct inode *inode = vi->inode;
+	const struct fsverity_hash_alg *hash_alg = vi->tree_params.hash_alg;
+	const u32 sig_size = le32_to_cpu(desc->sig_size);
+	struct fsverity_signed_digest *d;
+	int err;
+
+	if (sig_size == 0) {
+		if (fsverity_require_signatures) {
+			fsverity_err(inode,
+				     "require_signatures=1, rejecting unsigned file!");
+			return -EPERM;
+		}
+		return 0;
+	}
+
+	if (sig_size > desc_size - sizeof(*desc)) {
+		fsverity_err(inode, "Signature overflows verity descriptor");
+		return -EBADMSG;
+	}
+
+	d = kzalloc(sizeof(*d) + hash_alg->digest_size, GFP_KERNEL);
+	if (!d)
+		return -ENOMEM;
+	memcpy(d->magic, "FSVerity", 8);
+	d->digest_algorithm = cpu_to_le16(hash_alg - fsverity_hash_algs);
+	d->digest_size = cpu_to_le16(hash_alg->digest_size);
+	memcpy(d->digest, vi->measurement, hash_alg->digest_size);
+
+	err = verify_pkcs7_signature(d, sizeof(*d) + hash_alg->digest_size,
+				     desc->signature, sig_size,
+				     fsverity_keyring,
+				     VERIFYING_UNSPECIFIED_SIGNATURE,
+				     NULL, NULL);
+	kfree(d);
+
+	if (err) {
+		if (err == -ENOKEY)
+			fsverity_err(inode,
+				     "File's signing cert isn't in the fs-verity keyring");
+		else if (err == -EKEYREJECTED)
+			fsverity_err(inode, "Incorrect file signature");
+		else if (err == -EBADMSG)
+			fsverity_err(inode, "Malformed file signature");
+		else
+			fsverity_err(inode, "Error %d verifying file signature",
+				     err);
+		return err;
+	}
+
+	pr_debug("Valid signature for file measurement %s:%*phN\n",
+		 hash_alg->name, hash_alg->digest_size, vi->measurement);
+	return 0;
+}
+
+#ifdef CONFIG_SYSCTL
+static struct ctl_table_header *fsverity_sysctl_header;
+
+static const struct ctl_path fsverity_sysctl_path[] = {
+	{ .procname = "fs", },
+	{ .procname = "verity", },
+	{ }
+};
+
+static struct ctl_table fsverity_sysctl_table[] = {
+	{
+		.procname       = "require_signatures",
+		.data           = &fsverity_require_signatures,
+		.maxlen         = sizeof(int),
+		.mode           = 0644,
+		.proc_handler   = proc_dointvec_minmax,
+		.extra1         = SYSCTL_ZERO,
+		.extra2         = SYSCTL_ONE,
+	},
+	{ }
+};
+
+static int __init fsverity_sysctl_init(void)
+{
+	fsverity_sysctl_header = register_sysctl_paths(fsverity_sysctl_path,
+						       fsverity_sysctl_table);
+	if (!fsverity_sysctl_header) {
+		pr_err("sysctl registration failed!\n");
+		return -ENOMEM;
+	}
+	return 0;
+}
+#else /* !CONFIG_SYSCTL */
+static inline int __init fsverity_sysctl_init(void)
+{
+	return 0;
+}
+#endif /* !CONFIG_SYSCTL */
+
+int __init fsverity_init_signature(void)
+{
+	struct key *ring;
+	int err;
+
+	ring = keyring_alloc(".fs-verity", KUIDT_INIT(0), KGIDT_INIT(0),
+			     current_cred(), KEY_POS_SEARCH |
+				KEY_USR_VIEW | KEY_USR_READ | KEY_USR_WRITE |
+				KEY_USR_SEARCH | KEY_USR_SETATTR,
+			     KEY_ALLOC_NOT_IN_QUOTA, NULL, NULL);
+	if (IS_ERR(ring))
+		return PTR_ERR(ring);
+
+	err = fsverity_sysctl_init();
+	if (err)
+		goto err_put_ring;
+
+	fsverity_keyring = ring;
+	return 0;
+
+err_put_ring:
+	key_put(ring);
+	return err;
+}