Add encrypted file support

In certain cases, such as network booting over an untrusted connection,
it may be useful to fully encrypt and sign the kernel files.

Enable fully encrypted boot using builtin keyring via the addition of
the string "ENCRYPTED" to the first line of the /etc/pb-lockdown file.
This disables detached (plaintext) signature verification.

Signed-off-by: Timothy Pearson <tpearson@raptorengineering.com>
Signed-off-by: Samuel Mendoza-Jonas <sam@mendozajonas.com>

2 files changed, 275 insertions, 28 deletions

diff --git a/lib/security/gpg.c b/lib/security/gpg.c
index a377b55..41d1306 100644
--- a/lib/security/gpg.c
+++ b/lib/security/gpg.c
@@ -60,6 +60,178 @@ struct pb_url * gpg_get_signature_url(void *ctx, struct pb_url *base_file)
 	return signature_file;
 }
 
+int decrypt_file(const char *filename,
+	FILE *authorized_signatures_handle, const char *keyring_path)
+{
+	int result = 0;
+	int valid = 0;
+	size_t bytes_read = 0;
+	unsigned char buffer[8192];
+
+	if (filename == NULL)
+		return -1;
+
+	gpgme_signature_t verification_signatures;
+	gpgme_verify_result_t verification_result;
+	gpgme_data_t ciphertext_data;
+	gpgme_data_t plaintext_data;
+	gpgme_engine_info_t enginfo;
+	gpgme_ctx_t gpg_context;
+	gpgme_error_t err;
+
+	/* Initialize gpgme */
+	setlocale (LC_ALL, "");
+	gpgme_check_version(NULL);
+	gpgme_set_locale(NULL, LC_CTYPE, setlocale (LC_CTYPE, NULL));
+	err = gpgme_engine_check_version(GPGME_PROTOCOL_OpenPGP);
+	if (err != GPG_ERR_NO_ERROR) {
+		pb_log("%s: OpenPGP support not available\n", __func__);
+		return -1;
+	}
+	err = gpgme_get_engine_info(&enginfo);
+	if (err != GPG_ERR_NO_ERROR) {
+		pb_log("%s: GPG engine failed to initialize\n", __func__);
+		return -1;
+	}
+	err = gpgme_new(&gpg_context);
+	if (err != GPG_ERR_NO_ERROR) {
+		pb_log("%s: GPG context could not be created\n", __func__);
+		return -1;
+	}
+	err = gpgme_set_protocol(gpg_context, GPGME_PROTOCOL_OpenPGP);
+	if (err != GPG_ERR_NO_ERROR) {
+		pb_log("%s: GPG protocol could not be set\n", __func__);
+		return -1;
+	}
+	if (keyring_path)
+		err = gpgme_ctx_set_engine_info (gpg_context,
+			GPGME_PROTOCOL_OpenPGP,
+			enginfo->file_name, keyring_path);
+	else
+		err = gpgme_ctx_set_engine_info (gpg_context,
+			GPGME_PROTOCOL_OpenPGP,
+			enginfo->file_name, enginfo->home_dir);
+	if (err != GPG_ERR_NO_ERROR) {
+		pb_log("%s: Could not set GPG engine information\n", __func__);
+		return -1;
+	}
+	err = gpgme_data_new(&plaintext_data);
+	if (err != GPG_ERR_NO_ERROR) {
+		pb_log("%s: Could not create GPG plaintext data buffer\n",
+			__func__);
+		return -1;
+	}
+	err = gpgme_data_new_from_file(&ciphertext_data, filename, 1);
+	if (err != GPG_ERR_NO_ERROR) {
+		pb_log("%s: Could not create GPG ciphertext data buffer"
+			" from file '%s'\n", __func__, filename);
+		return -1;
+	}
+
+	/* Decrypt and verify file */
+	err = gpgme_op_decrypt_verify(gpg_context, ciphertext_data,
+		plaintext_data);
+	if (err != GPG_ERR_NO_ERROR) {
+		pb_log("%s: Could not decrypt file\n", __func__);
+		return -1;
+	}
+	verification_result = gpgme_op_verify_result(gpg_context);
+	verification_signatures = verification_result->signatures;
+	while (verification_signatures) {
+		if (verification_signatures->status == GPG_ERR_NO_ERROR) {
+			pb_log("%s: Good signature for key ID '%s' ('%s')\n",
+				__func__,
+				verification_signatures->fpr, filename);
+			/* Verify fingerprint is present in authorized
+			 * signatures file
+			 */
+			char *auth_sig_line = NULL;
+			size_t auth_sig_len = 0;
+			ssize_t auth_sig_read;
+			rewind(authorized_signatures_handle);
+			while ((auth_sig_read = getline(&auth_sig_line,
+				&auth_sig_len,
+				authorized_signatures_handle)) != -1) {
+				auth_sig_len = strlen(auth_sig_line);
+				while ((auth_sig_line[auth_sig_len-1] == '\n')
+					|| (auth_sig_line[auth_sig_len-1] == '\r'))
+					auth_sig_len--;
+				auth_sig_line[auth_sig_len] = 0;
+				if (strcmp(auth_sig_line,
+					verification_signatures->fpr) == 0)
+					valid = 1;
+			}
+			free(auth_sig_line);
+		}
+		else {
+			pb_log("%s: Signature for key ID '%s' ('%s') invalid."
+				"  Status: %08x\n", __func__,
+				verification_signatures->fpr, filename,
+				verification_signatures->status);
+		}
+		verification_signatures = verification_signatures->next;
+	}
+
+	gpgme_data_release(ciphertext_data);
+
+	if (valid) {
+		/* Write decrypted file over ciphertext */
+		FILE *plaintext_file_handle = NULL;
+		plaintext_file_handle = fopen(filename, "wb");
+		if (!plaintext_file_handle) {
+			pb_log("%s: Could not create GPG plaintext file '%s'\n",
+				__func__, filename);
+			gpgme_data_release(plaintext_data);
+			gpgme_release(gpg_context);
+			return -1;
+		}
+		gpgme_data_seek(plaintext_data, 0, SEEK_SET);
+		if (err != GPG_ERR_NO_ERROR) {
+			pb_log("%s: Could not seek in GPG plaintext buffer\n",
+				__func__);
+			gpgme_data_release(plaintext_data);
+			gpgme_release(gpg_context);
+			fclose(plaintext_file_handle);
+			return -1;
+		}
+		while ((bytes_read = gpgme_data_read(plaintext_data, buffer,
+			8192)) > 0) {
+			size_t l2 = fwrite(buffer, 1, bytes_read,
+				plaintext_file_handle);
+			if (l2 < bytes_read) {
+				if (ferror(plaintext_file_handle)) {
+					/* General error */
+					result = -1;
+					pb_log("%s: failed: unknown fault\n",
+						__func__);
+				}
+				else {
+					/* No space on destination device */
+					result = -1;
+					pb_log("%s: failed: temporary storage"
+						" full\n", __func__);
+				}
+				break;
+			}
+		}
+		fclose(plaintext_file_handle);
+	}
+
+	/* Clean up */
+	gpgme_data_release(plaintext_data);
+	gpgme_release(gpg_context);
+
+	if (!valid) {
+		pb_log("%s: Incorrect GPG signature\n", __func__);
+		return -1;
+	}
+
+	pb_log("%s: GPG signature for decrypted file '%s' verified\n",
+		__func__, filename);
+
+	return result;
+}
+
 int verify_file_signature(const char *plaintext_filename,
 	const char *signature_filename, FILE *authorized_signatures_handle,
 	const char *keyring_path)
@@ -208,10 +380,11 @@ int gpg_validate_boot_files(struct boot_task *boot_task) {
 		boot_task->local_dtb_signature : NULL;
 	const char* local_image_signature = (boot_task->verify_signature) ?
 		boot_task->local_image_signature : NULL;
-	const char* local_cmdline_signature = (boot_task->verify_signature) ?
+	const char* local_cmdline_signature =
+		(boot_task->verify_signature || boot_task->decrypt_files) ?
 		boot_task->local_cmdline_signature : NULL;
 
-	if (!boot_task->verify_signature)
+	if ((!boot_task->verify_signature) && (!boot_task->decrypt_files))
 		return result;
 
 	/* Load authorized signatures file */
@@ -283,38 +456,71 @@ int gpg_validate_boot_files(struct boot_task *boot_task) {
 		fflush(cmdline_handle);
 	}
 
-	/* Check signatures */
-	if (verify_file_signature(kernel_filename,
-		local_image_signature,
-		authorized_signatures_handle, "/etc/gpg"))
-		result = KEXEC_LOAD_SIGNATURE_FAILURE;
-	if (verify_file_signature(cmdline_template,
-		local_cmdline_signature,
-		authorized_signatures_handle, "/etc/gpg"))
-		result = KEXEC_LOAD_SIGNATURE_FAILURE;
-	if (boot_task->local_initrd_signature)
-		if (verify_file_signature(initrd_filename,
-			local_initrd_signature,
-			authorized_signatures_handle, "/etc/gpg"))
-			result = KEXEC_LOAD_SIGNATURE_FAILURE;
-	if (boot_task->local_dtb_signature)
-		if (verify_file_signature(dtb_filename,
-			local_dtb_signature,
-			authorized_signatures_handle, "/etc/gpg"))
+	if (boot_task->verify_signature) {
+		/* Check signatures */
+		if (verify_file_signature(kernel_filename,
+			local_image_signature,
+			authorized_signatures_handle,
+			"/etc/gpg"))
+		if (verify_file_signature(cmdline_template,
+			local_cmdline_signature,
+			authorized_signatures_handle,
+			"/etc/gpg"))
+
+		if (boot_task->local_initrd_signature)
+			if (verify_file_signature(initrd_filename,
+				local_initrd_signature,
+				authorized_signatures_handle,
+				"/etc/gpg"))
+				result = KEXEC_LOAD_SIGNATURE_FAILURE;
+		if (boot_task->local_dtb_signature)
+			if (verify_file_signature(dtb_filename,
+				local_dtb_signature,
+				authorized_signatures_handle,
+				"/etc/gpg"))
+				result = KEXEC_LOAD_SIGNATURE_FAILURE;
+
+		/* Clean up */
+		if (cmdline_handle) {
+			fclose(cmdline_handle);
+			unlink(cmdline_template);
+		}
+		fclose(authorized_signatures_handle);
+	} else if (boot_task->decrypt_files) {
+		/* Decrypt files */
+		if (decrypt_file(kernel_filename,
+			authorized_signatures_handle,
+			"/etc/gpg"))
+			result = KEXEC_LOAD_DECRYPTION_FALURE;
+		if (verify_file_signature(cmdline_template,
+			local_cmdline_signature,
+			authorized_signatures_handle,
+			"/etc/gpg"))
 			result = KEXEC_LOAD_SIGNATURE_FAILURE;
+		if (boot_task->local_initrd)
+		if (decrypt_file(initrd_filename,
+				authorized_signatures_handle,
+				"/etc/gpg"))
+				result = KEXEC_LOAD_DECRYPTION_FALURE;
+		if (boot_task->local_dtb)
+			if (decrypt_file(dtb_filename,
+				authorized_signatures_handle,
+				"/etc/gpg"))
+				result = KEXEC_LOAD_DECRYPTION_FALURE;
 
-	/* Clean up */
-	if (cmdline_handle) {
-		fclose(cmdline_handle);
-		unlink(cmdline_template);
+		/* Clean up */
+		if (cmdline_handle) {
+			fclose(cmdline_handle);
+			unlink(cmdline_template);
+		}
+		fclose(authorized_signatures_handle);
 	}
-	fclose(authorized_signatures_handle);
 
 	return result;
 }
 
 void gpg_validate_boot_files_cleanup(struct boot_task *boot_task) {
-	if (boot_task->verify_signature) {
+	if ((boot_task->verify_signature) || (boot_task->decrypt_files)) {
 		unlink(boot_task->local_image_override);
 		if (boot_task->local_initrd_override)
 			unlink(boot_task->local_initrd_override);
@@ -330,8 +536,38 @@ void gpg_validate_boot_files_cleanup(struct boot_task *boot_task) {
 }
 
 int lockdown_status() {
+	/* assume most restrictive lockdown type */
+	int ret = PB_LOCKDOWN_SIGN;
+
 	if (access(LOCKDOWN_FILE, F_OK) == -1)
 		return PB_LOCKDOWN_NONE;
-	else
-		return PB_LOCKDOWN_SIGN;
+
+	/* determine lockdown type */
+	FILE *authorized_signatures_handle = NULL;
+	authorized_signatures_handle = fopen(LOCKDOWN_FILE, "r");
+	if (!authorized_signatures_handle)
+		return ret;
+
+	char *auth_sig_line = NULL;
+	size_t auth_sig_len = 0;
+	ssize_t auth_sig_read;
+	rewind(authorized_signatures_handle);
+	if ((auth_sig_read = getline(&auth_sig_line,
+		&auth_sig_len,
+		authorized_signatures_handle)) != -1) {
+		auth_sig_len = strlen(auth_sig_line);
+		while ((auth_sig_line[auth_sig_len-1] == '\n')
+			|| (auth_sig_line[auth_sig_len-1] == '\r'))
+		auth_sig_len--;
+		auth_sig_line[auth_sig_len] = 0;
+		if (strcmp(auth_sig_line, "ENCRYPTED") == 0) {
+			/* first line indicates encrypted files
+			 * expected.  enable decryption.
+			 */
+			ret = PB_LOCKDOWN_DECRYPT;
+		}
+	}
+	free(auth_sig_line);
+
+	return ret;
 }
\ No newline at end of file
diff --git a/lib/security/gpg.h b/lib/security/gpg.h
index fb418bb..6efc3d2 100644
--- a/lib/security/gpg.h
+++ b/lib/security/gpg.h
@@ -23,6 +23,7 @@
 enum {
 	PB_LOCKDOWN_NONE	= 0,
 	PB_LOCKDOWN_SIGN	= 1,
+	PB_LOCKDOWN_DECRYPT	= 2,
 };
 
 #if defined(HAVE_LIBGPGME)
@@ -37,6 +38,9 @@ int verify_file_signature(const char *plaintext_filename,
 	const char *signature_filename, FILE *authorized_signatures_handle,
 	const char *keyring_path);
 
+int decrypt_file(const char * filename,
+	FILE * authorized_signatures_handle, const char * keyring_path);
+
 int gpg_validate_boot_files(struct boot_task *boot_task);
 
 void gpg_validate_boot_files_cleanup(struct boot_task *boot_task);
@@ -59,6 +63,13 @@ int verify_file_signature(const char *plaintext_filename __attribute__((unused))
 	return -1;
 }
 
+int decrypt_file(const char * filename __attribute__((unused)),
+	FILE * authorized_signatures_handle __attribute__((unused)),
+	const char * keyring_path __attribute__((unused)))
+{
+	return -1;
+}
+
 int gpg_validate_boot_files(struct boot_task *boot_task __attribute__((unused)))
 {
 	return 0;