[crypto] Add PEM image format

Add PEM-encoded ASN.1 as an image format.  We accept as PEM any image
containing a line starting with a "-----BEGIN" boundary marker.

We allow for PEM files containing multiple ASN.1 objects, such as a
certificate chain produced by concatenating individual certificate
files.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/image/pem.c

@@ -0,0 +1,208 @@
+/*
+ * Copyright (C) 2016 Michael Brown <mbrown@fensystems.co.uk>.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation; either version 2 of the
+ * License, or any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+ * 02110-1301, USA.
+ *
+ * You can also choose to distribute this program under the terms of
+ * the Unmodified Binary Distribution Licence (as given in the file
+ * COPYING.UBDL), provided that you have satisfied its requirements.
+ */
+
+FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
+
+#include <stdlib.h>
+#include <errno.h>
+#include <assert.h>
+#include <ipxe/asn1.h>
+#include <ipxe/pem.h>
+#include <ipxe/base64.h>
+#include <ipxe/uaccess.h>
+#include <ipxe/image.h>
+
+/** @file
+ *
+ * PEM-encoded ASN.1 data
+ *
+ */
+
+/**
+ * Locate next line
+ *
+ * @v image		PEM image
+ * @v offset		Starting offset
+ * @ret next		Offset to next line
+ */
+static size_t pem_next ( struct image *image, size_t offset ) {
+	off_t eol;
+
+	/* Find and skip next newline character, if any */
+	eol = memchr_user ( image->data, offset, '\n', ( image->len - offset ));
+	if ( eol < 0 )
+		return image->len;
+	return ( eol + 1 );
+}
+
+/**
+ * Locate boundary marker line
+ *
+ * @v image		PEM image
+ * @v offset		Starting offset
+ * @v marker		Boundary marker
+ * @ret offset		Offset to boundary marker line, or negative error
+ */
+static int pem_marker ( struct image *image, size_t offset,
+			const char *marker ) {
+	char buf[ strlen ( marker ) ];
+
+	/* Sanity check */
+	assert ( offset <= image->len );
+
+	/* Scan for marker at start of line */
+	while ( offset < image->len ) {
+
+		/* Check for marker */
+		if ( ( image->len - offset ) < sizeof ( buf ) )
+			break;
+		copy_from_user ( buf, image->data, offset, sizeof ( buf ) );
+		if ( memcmp ( buf, marker, sizeof ( buf ) ) == 0 )
+			return offset;
+
+		/* Move to next line */
+		offset = pem_next ( image, offset );
+		assert ( offset <= image->len );
+	}
+
+	return -ENOENT;
+}
+
+/**
+ * Extract ASN.1 object from image
+ *
+ * @v image		PEM image
+ * @v offset		Offset within image
+ * @v cursor		ASN.1 cursor to fill in
+ * @ret next		Offset to next image, or negative error
+ *
+ * The caller is responsible for eventually calling free() on the
+ * allocated ASN.1 cursor.
+ */
+static int pem_asn1 ( struct image *image, size_t offset,
+		      struct asn1_cursor **cursor ) {
+	size_t encoded_len;
+	size_t decoded_max_len;
+	char *encoded;
+	void *decoded;
+	int begin;
+	int end;
+	int len;
+	int rc;
+
+	/* Locate and skip BEGIN marker */
+	begin = pem_marker ( image, offset, PEM_BEGIN );
+	if ( begin < 0 ) {
+		rc = begin;
+		DBGC ( image, "PEM %s [%#zx,%#zx) missing BEGIN marker: %s\n",
+		       image->name, offset, image->len, strerror ( rc ) );
+		goto err_begin;
+	}
+	begin = pem_next ( image, begin );
+
+	/* Locate and skip END marker */
+	end = pem_marker ( image, begin, PEM_END );
+	if ( end < 0 ) {
+		rc = end;
+		DBGC ( image, "PEM %s [%#zx,%#zx) missing END marker: %s\n",
+		       image->name, offset, image->len, strerror ( rc ) );
+		goto err_end;
+	}
+	encoded_len = ( end - begin );
+	end = pem_next ( image, end );
+
+	/* Extract Base64-encoded data */
+	encoded = malloc ( encoded_len + 1 /* NUL */ );
+	if ( ! encoded ) {
+		rc = -ENOMEM;
+		goto err_alloc_encoded;
+	}
+	copy_from_user ( encoded, image->data, begin, encoded_len );
+	encoded[encoded_len] = '\0';
+
+	/* Allocate cursor and data buffer */
+	decoded_max_len = base64_decoded_max_len ( encoded );
+	*cursor = malloc ( sizeof ( **cursor ) + decoded_max_len );
+	if ( ! *cursor ) {
+		rc = -ENOMEM;
+		goto err_alloc_decoded;
+	}
+	decoded = ( ( ( void * ) *cursor ) + sizeof ( **cursor ) );
+
+	/* Decode Base64-encoded data */
+	len = base64_decode ( encoded, decoded, decoded_max_len );
+	if ( len < 0 ) {
+		rc = len;
+		DBGC ( image, "PEM %s could not decode: %s\n",
+		       image->name, strerror ( rc ) );
+		goto err_decode;
+	}
+	(*cursor)->data = decoded;
+	(*cursor)->len = len;
+	assert ( (*cursor)->len <= decoded_max_len );
+
+	/* Free Base64-encoded data */
+	free ( encoded );
+
+	/* Update offset and skip any unencapsulated trailer */
+	offset = end;
+	if ( pem_marker ( image, offset, PEM_BEGIN ) < 0 )
+		offset = image->len;
+
+	return offset;
+
+ err_decode:
+	free ( decoded );
+ err_alloc_decoded:
+	free ( encoded );
+ err_alloc_encoded:
+ err_end:
+ err_begin:
+	return rc;
+}
+
+/**
+ * Probe PEM image
+ *
+ * @v image		PEM image
+ * @ret rc		Return status code
+ */
+static int pem_probe ( struct image *image ) {
+	int rc;
+
+	/* Check that image contains a BEGIN marker */
+	if ( ( rc = pem_marker ( image, 0, PEM_BEGIN ) ) < 0 ) {
+		DBGC ( image, "PEM %s has no BEGIN marker: %s\n",
+		       image->name, strerror ( rc ) );
+		return rc;
+	}
+
+	return 0;
+}
+
+/** PEM image type */
+struct image_type pem_image_type __image_type ( PROBE_NORMAL ) = {
+	.name = "PEM",
+	.probe = pem_probe,
+	.asn1 = pem_asn1,
+};