Merge lp:~wlxing/ecryptfs/lp342398 into lp:ecryptfs

[Jason Xing]

Add ecryptfs-stat support for encrypted filenames (LP: #342398). The main process has three parts: decoding filename, parsing filename and printing information.
Test output samples:
Case 1):
[...]
Filename encryption enabled
FNEK sig is [8f9887d2339cafb0]
Filename encrytion cipher is [aes]
Case 2):
[...]
Filename encryption disabled
Case 3):
[...]
Filename encryption enabled
ecryptfs_parse_tag_70_packet: max_packet_size is [42]; real packet size is [35]
ecryptfs_parse_filename: Could not parse tag 70 packet from filename

Unmerged revisions

895. By Jason Xing on 2017-06-10

src/utils/ecryptfs-stat.c, src/libecryptfs/ecryptfs-stat.c, src/include/ecryptfs.h: Add ecryptfs-stat support for encrypted filenames (LP: #342398)

=== modified file 'debian/changelog'
--- debian/changelog	2017-06-08 23:29:22 +0000
+++ debian/changelog	2017-06-10 01:37:57 +0000
@@ -36,6 +36,8 @@
     users that even though the mount was successful, their data may not be
     decrypted when a mount passphrase was used for recovery
     (LP: #1694272, LP: #1439825)
+  * src/utils/ecryptfs-stat.c, src/libecryptfs/ecryptfs-stat.c, src/include/ecryptfs.h: 
+    Add ecryptfs-stat support for encrypted filenames. (LP: #342398)
 
   [ Jelle van der Waa ]
   * src/key_mod/ecryptfs_key_mod_openssl.c,
 
=== modified file 'src/include/ecryptfs.h'
--- src/include/ecryptfs.h	2015-02-14 22:11:29 +0000
+++ src/include/ecryptfs.h	2017-06-10 01:37:57 +0000
@@ -94,6 +94,7 @@
 #define MAGIC_ECRYPTFS_MARKER 0x3c81b7f5
 #define MAGIC_ECRYPTFS_MARKER_SIZE_BYTES 8	/* 4*2 */
 #endif
+#define ECRYPTFS_MAX_CIPHER_NAME_SIZE 32
 #define MAX_NAME_SIZE 128
 #define MAX_KEY_MOD_VALUE_SIZE 4096
 #define ECRYPTFS_TAG_1_PACKET_TYPE 0x01
@@ -103,6 +104,7 @@
 #define ECRYPTFS_TAG_65_PACKET_TYPE 0x41
 #define ECRYPTFS_TAG_66_PACKET_TYPE 0x42
 #define ECRYPTFS_TAG_67_PACKET_TYPE 0x43
+#define ECRYPTFS_TAG_70_PACKET_TYPE 0x46
 #define ECRYPTFS_MSG_HELO 100
 #define ECRYPTFS_MSG_QUIT 101
 #define ECRYPTFS_MSG_REQUEST 102
@@ -143,6 +145,21 @@
 #define ECRYPTFS_ECHO_ON 1
 #define ECRYPTFS_ECHO_OFF 0
 
+#define ECRYPTFS_FNEK_ENCRYPTED_FILENAME_PREFIX "ECRYPTFS_FNEK_ENCRYPTED."
+#define ECRYPTFS_FNEK_ENCRYPTED_FILENAME_PREFIX_SIZE 24
+#define ECRYPTFS_MIN_PKT_LEN_SIZE 1
+#define ECRYPTFS_TAG_70_MIN_METADATA_SIZE (1 + ECRYPTFS_MIN_PKT_LEN_SIZE \
+					   + ECRYPTFS_SIG_SIZE + 1 + 1)
+
+#define RFC2440_CIPHER_DES3_EDE 0x02
+#define RFC2440_CIPHER_CAST_5 0x03
+#define RFC2440_CIPHER_BLOWFISH 0x04
+#define RFC2440_CIPHER_AES_128 0x07
+#define RFC2440_CIPHER_AES_192 0x08
+#define RFC2440_CIPHER_AES_256 0x09
+#define RFC2440_CIPHER_TWOFISH 0x0a
+#define RFC2440_CIPHER_CAST_6 0x0b
+
 #define ECRYPTFS_AES_BLOCK_SIZE 16
 #define ECRYPTFS_AES_KEY_BYTES 16
 
@@ -437,6 +454,7 @@
 #define ECRYPTFS_METADATA_IN_XATTR  0x00000100
 #define ECRYPTFS_VIEW_AS_ENCRYPTED  0x00000200
 #define ECRYPTFS_KEY_SET            0x00000400
+#define ECRYPTFS_ENCRYPT_FILENAMES  0x00000800
 	uint32_t flags;
 	unsigned int file_version;
 	uint64_t file_size;
@@ -580,4 +598,6 @@
 char *ecryptfs_fetch_private_mnt(char *pw_dir);
 int ecryptfs_private_is_mounted(char *dev, char *mnt, char *sig, int mounting);
 
+int ecryptfs_parse_filename(const char *path, size_t path_len);
+
 #endif
 
=== modified file 'src/libecryptfs/ecryptfs-stat.c'
--- src/libecryptfs/ecryptfs-stat.c	2013-10-27 22:21:20 +0000
+++ src/libecryptfs/ecryptfs-stat.c	2017-06-10 01:37:57 +0000
@@ -65,7 +65,8 @@
 static struct ecryptfs_flag_map_elem ecryptfs_flag_map[] = {
 	{0x00000001, ECRYPTFS_ENABLE_HMAC},
 	{0x00000002, ECRYPTFS_ENCRYPTED},
-	{0x00000004, ECRYPTFS_METADATA_IN_XATTR}
+	{0x00000004, ECRYPTFS_METADATA_IN_XATTR},
+	{0x00000008, ECRYPTFS_ENCRYPT_FILENAMES}
 };
 
 /**
@@ -186,3 +187,323 @@
 out:
 	return rc;
 }
+
+/* We could either offset on every reverse map or just pad some 0x00's
+ * at the front here */
+static const unsigned char filename_rev_map[256] = {
+	0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, /* 7 */
+	0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, /* 15 */
+	0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, /* 23 */
+	0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, /* 31 */
+	0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, /* 39 */
+	0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01, 0x00, /* 47 */
+	0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, /* 55 */
+	0x0A, 0x0B, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, /* 63 */
+	0x00, 0x0C, 0x0D, 0x0E, 0x0F, 0x10, 0x11, 0x12, /* 71 */
+	0x13, 0x14, 0x15, 0x16, 0x17, 0x18, 0x19, 0x1A, /* 79 */
+	0x1B, 0x1C, 0x1D, 0x1E, 0x1F, 0x20, 0x21, 0x22, /* 87 */
+	0x23, 0x24, 0x25, 0x00, 0x00, 0x00, 0x00, 0x00, /* 95 */
+	0x00, 0x26, 0x27, 0x28, 0x29, 0x2A, 0x2B, 0x2C, /* 103 */
+	0x2D, 0x2E, 0x2F, 0x30, 0x31, 0x32, 0x33, 0x34, /* 111 */
+	0x35, 0x36, 0x37, 0x38, 0x39, 0x3A, 0x3B, 0x3C, /* 119 */
+	0x3D, 0x3E, 0x3F /* 123 - 255 initialized to 0x00 */
+};
+
+static size_t ecryptfs_max_decoded_size(size_t encoded_size)
+{
+	/* Not exact; conservatively long. Every block of 4
+	 * encoded characters decodes into a block of 3
+	 * decoded characters. This segment of code provides
+	 * the caller with the maximum amount of allocated
+	 * space that @dst will need to point to in a
+	 * subsequent call. */
+	return ((encoded_size + 1) * 3) / 4;
+}
+
+/**
+ * ecryptfs_decode_from_filename
+ * @dst: If NULL, this function only sets @dst_size and returns. If
+ *       non-NULL, this function decodes the encoded octets in @src
+ *       into the memory that @dst points to.
+ * @dst_size: Set to the size of the decoded string.
+ * @src: The encoded set of octets to decode.
+ * @src_size: The size of the encoded set of octets to decode.
+ */
+static void
+ecryptfs_decode_from_filename(unsigned char *dst, size_t *dst_size,
+			      const unsigned char *src, size_t src_size)
+{
+	unsigned char current_bit_offset = 0;
+	size_t src_byte_offset = 0;
+	size_t dst_byte_offset = 0;
+
+	if (dst == NULL) {
+		(*dst_size) = ecryptfs_max_decoded_size(src_size);
+		goto out;
+	}
+	while (src_byte_offset < src_size) {
+		unsigned char src_byte =
+				filename_rev_map[(int)src[src_byte_offset]];
+
+		switch (current_bit_offset) {
+		case 0:
+			dst[dst_byte_offset] = (src_byte << 2);
+			current_bit_offset = 6;
+			break;
+		case 6:
+			dst[dst_byte_offset++] |= (src_byte >> 4);
+			dst[dst_byte_offset] = ((src_byte & 0xF)
+						 << 4);
+			current_bit_offset = 4;
+			break;
+		case 4:
+			dst[dst_byte_offset++] |= (src_byte >> 2);
+			dst[dst_byte_offset] = (src_byte << 6);
+			current_bit_offset = 2;
+			break;
+		case 2:
+			dst[dst_byte_offset++] |= (src_byte);
+			dst[dst_byte_offset] = 0;
+			current_bit_offset = 0;
+			break;
+		}
+		src_byte_offset++;
+	}
+	(*dst_size) = dst_byte_offset;
+out:
+	return;
+}
+
+static int ecryptfs_decode_filename(const char *name, size_t name_size, 
+								char **decoded_name, size_t *decoded_name_size)
+{
+	int rc = 0;
+
+	if ((name_size > ECRYPTFS_FNEK_ENCRYPTED_FILENAME_PREFIX_SIZE) 
+		&& (strncmp(name, ECRYPTFS_FNEK_ENCRYPTED_FILENAME_PREFIX, 
+			ECRYPTFS_FNEK_ENCRYPTED_FILENAME_PREFIX_SIZE) == 0)) {
+		name += ECRYPTFS_FNEK_ENCRYPTED_FILENAME_PREFIX_SIZE;
+		name_size -= ECRYPTFS_FNEK_ENCRYPTED_FILENAME_PREFIX_SIZE;
+		ecryptfs_decode_from_filename(NULL, decoded_name_size,
+								name, name_size);
+		(*decoded_name) = (char *)malloc(*decoded_name_size);
+		if (!(*decoded_name)) {
+			printf("%s: Out of memory whilst attempting "
+			       "to malloc [%zd] bytes\n", __func__,
+			       *decoded_name_size);
+			rc = -ENOMEM;
+			goto out;
+		}
+		ecryptfs_decode_from_filename(*decoded_name, decoded_name_size,
+					      name, name_size);
+	} else {
+		rc = -EINVAL;
+	}
+out:
+	return rc;
+}
+
+struct ecryptfs_parse_tag_70_packet_stack {
+	unsigned char cipher_code;
+	size_t max_packet_size;
+	size_t packet_size_len;
+	size_t parsed_tag_70_packet_size;
+	size_t block_aligned_filename_size;	
+	char fnek_sig_hex[ECRYPTFS_SIG_SIZE_HEX + 1];
+	char cipher_string[ECRYPTFS_MAX_CIPHER_NAME_SIZE];
+};
+
+struct ecryptfs_cipher_code_str_map_elem {
+	char cipher_str[16];
+	unsigned char cipher_code;
+};
+
+/* For now eCryptfs doesn't support public-key type for 
+ * filename encrytion/decrption*/
+static struct ecryptfs_cipher_code_str_map_elem
+ecryptfs_cipher_code_str_map[] = {
+	{"aes",RFC2440_CIPHER_AES_128 },
+	{"blowfish", RFC2440_CIPHER_BLOWFISH},
+	{"des3_ede", RFC2440_CIPHER_DES3_EDE},
+	{"cast5", RFC2440_CIPHER_CAST_5},
+	{"twofish", RFC2440_CIPHER_TWOFISH},
+	{"cast6", RFC2440_CIPHER_CAST_6},
+	{"aes", RFC2440_CIPHER_AES_192},
+	{"aes", RFC2440_CIPHER_AES_256}
+};
+
+/**
+ * ecryptfs_cipher_code_to_string
+ * @str: Destination to write out the cipher name
+ * @cipher_code: The code to convert to cipher name string
+ *
+ * Returns zero on success
+ */
+static int ecryptfs_cipher_code_to_string(char *str, unsigned char cipher_code)
+{
+	int rc = 0;
+	int i;
+
+	str[0] = '\0';
+	for (i = 0; i < (sizeof(ecryptfs_cipher_code_str_map) / sizeof(ecryptfs_cipher_code_str_map[0])); i++)
+		if (cipher_code == ecryptfs_cipher_code_str_map[i].cipher_code)
+			strcpy(str, ecryptfs_cipher_code_str_map[i].cipher_str);
+	if (str[0] == '\0') {
+		printf("Cipher code not recognized: [%d]\n", cipher_code);
+		rc = -EINVAL;
+	}
+	return rc;
+}
+
+/**
+ * ecryptfs_to_hex
+ * @dst: Buffer to take hex character representation of contents of
+ *       src; must be at least of size (src_size * 2)
+ * @src: Buffer to be converted to a hex string respresentation
+ * @src_size: number of bytes to convert
+ */
+static void ecryptfs_to_hex(char *dst, char *src, size_t src_size)
+{
+	int x;
+
+	for (x = 0; x < src_size; x++)
+		sprintf(&dst[x * 2], "%.2x", (unsigned char)src[x]);
+}
+
+/**
+ * parse_tag_70_packet - Parse and process FNEK-encrypted passphrase packet
+ * Tag 70 packet format:
+ * 		Octet 0: Tag 70 identifier
+ * 		Octets 1-N1: Tag 70 packet size (includes cipher identifier
+ *              		and block-aligned encrypted filename size)
+ * 		Octets N1-N2: FNEK sig (ECRYPTFS_SIG_SIZE)
+ * 		Octet N2-N3: Cipher identifier (1 octet)
+ * 		Octets N3-N4: Block-aligned encrypted filename
+ * 
+ * @s: Parse tag 70 packet into this structure and print its members one by 
+ * 	   one later
+ * @packet_size: This function sets this to the the number of octets
+ *               in the packet parsed
+ * @data: The memory location containing the start of the tag 70
+ *        packet
+ * @max_packet_size: The maximum legal size of the packet to be parsed
+ *                   from @data
+ *
+ * Returns zero on success; non-zero otherwise
+ */
+static int ecryptfs_parse_tag_70_packet(struct ecryptfs_parse_tag_70_packet_stack **s, size_t *packet_size, 
+						char *data, size_t max_packet_size)
+{
+	int rc = 0;
+
+	(*packet_size) = 0;
+	*s = (struct ecryptfs_parse_tag_70_packet_stack *)malloc(sizeof(**s));
+	if (!(*s)) {
+		printf("%s: Out of memory whilst trying to malloc "
+		       "[%zd] bytes of memory\n", __func__, sizeof(**s));
+		rc = -ENOMEM;
+		goto out;
+	}
+	if (max_packet_size < ECRYPTFS_TAG_70_MIN_METADATA_SIZE) {
+		printf("%s: max_packet_size is [%zd]; it must be "
+		       "at least [%d]\n", __func__, max_packet_size,
+		       ECRYPTFS_TAG_70_MIN_METADATA_SIZE);
+		rc = -EINVAL;
+		goto out;
+	}
+	/* Tag 70 identifier */
+	if (data[(*packet_size)++] != ECRYPTFS_TAG_70_PACKET_TYPE) {
+		printf("%s: Invalid packet tag [0x%.2x]; must be "
+		       "tag [0x%.2x]\n", __func__,
+		       data[((*packet_size) - 1)], ECRYPTFS_TAG_70_PACKET_TYPE);
+		rc = -EINVAL;
+		goto out;
+	}
+	/* Tag 70 packet size */
+	rc = ecryptfs_parse_packet_length(&data[(*packet_size)],
+					  &(*s)->parsed_tag_70_packet_size,
+					  &(*s)->packet_size_len);
+	if (rc) {
+		printf("%s: Error parsing packet length; "
+		       "rc = [%d]\n", __func__, rc);
+		goto out;
+	}
+	(*s)->block_aligned_filename_size = ((*s)->parsed_tag_70_packet_size
+					  - ECRYPTFS_SIG_SIZE - 1);
+	if ((1 + (*s)->packet_size_len + (*s)->parsed_tag_70_packet_size)
+	    > max_packet_size) {
+		printf("%s: max_packet_size is [%zd]; real packet "
+		       "size is [%zd]\n", __func__, max_packet_size,
+		       (1 + (*s)->packet_size_len + 1
+			+ (*s)->block_aligned_filename_size));
+		rc = -EINVAL;
+		goto out;
+	}
+	(*packet_size) += (*s)->packet_size_len;
+	/* FNEK sig */
+	ecryptfs_to_hex((*s)->fnek_sig_hex, &data[(*packet_size)],
+			ECRYPTFS_SIG_SIZE);
+	(*s)->fnek_sig_hex[ECRYPTFS_SIG_SIZE_HEX] = '\0';
+	(*packet_size) += ECRYPTFS_SIG_SIZE;
+	/* Cipher identifier */
+	(*s)->cipher_code = data[(*packet_size)++];
+	rc = ecryptfs_cipher_code_to_string((*s)->cipher_string, (*s)->cipher_code);
+	if (rc) {
+		printf("%s: Cipher code [%d] is invalid\n",
+		       __func__, (*s)->cipher_code);
+		goto out;
+	}
+out:
+	return rc;
+}
+
+static void ecryptfs_print_stack(struct ecryptfs_parse_tag_70_packet_stack *s)
+{
+	printf("FNEK sig is [%s]\n", s->fnek_sig_hex);
+	printf("Filename encrytion cipher is [%s]\n", s->cipher_string);
+	return;
+}
+
+/*
+ * find filename portion of a path (/foo/bar -> baz)
+ */
+static char *ecryptfs_get_filename(const char *s, int len)
+{
+	const char *e = s + len;
+
+	while (e != s && *(e-1) != '/')
+		e--;
+	return (char *)e;
+}
+
+int ecryptfs_parse_filename(const char *path, size_t path_len)
+{
+	const char *name;
+	char *decoded_name = NULL;
+	struct ecryptfs_parse_tag_70_packet_stack *s = NULL;
+	size_t name_size, decoded_name_size, packet_size;
+	int rc = 0;
+
+	name = ecryptfs_get_filename(path, path_len);
+	name_size = strlen(name);
+	rc = ecryptfs_decode_filename(name, name_size,
+					&decoded_name, &decoded_name_size);
+	if (rc) {
+		printf("%s: Could not decode filename\n", __func__);
+		goto out;
+	}
+	rc = ecryptfs_parse_tag_70_packet(&s,
+					  &packet_size,
+					  decoded_name,
+					  decoded_name_size);
+	if (rc) {
+		goto out;
+	}
+	ecryptfs_print_stack(s);
+out:
+	if (s)
+		free(s);
+	if (decoded_name)
+		free(decoded_name);
+	return rc;
+}
 
=== modified file 'src/utils/ecryptfs-stat.c'
--- src/utils/ecryptfs-stat.c	2009-02-03 08:50:36 +0000
+++ src/utils/ecryptfs-stat.c	2017-06-10 01:37:57 +0000
@@ -3,6 +3,7 @@
  */
 
 #include <stdio.h>
+#include <string.h>
 #include <fcntl.h>
 #include <unistd.h>
 #include <errno.h>
@@ -19,6 +20,7 @@
 int main(int argc, const char *argv[])
 {
 	const char *filename;
+	size_t filename_size;
 	int fd = -1;
 	ssize_t quant_read;
 	struct ecryptfs_crypt_stat_user crypt_stat;
@@ -30,6 +32,7 @@
 		goto out;
 	}
 	filename = argv[1];
+	filename_size = strlen(filename);
 	fd = open(filename, O_RDONLY);
 	if (fd == -1) {
 		printf("Error opening file [%s] for RD_ONLY access; errno msg "
@@ -68,6 +71,13 @@
 		printf("HMAC enabled\n");
 	else
 		printf("HMAC disabled\n");
+	if (crypt_stat.flags & ECRYPTFS_ENCRYPT_FILENAMES) {
+		printf("Filename encryption enabled\n");
+		rc = ecryptfs_parse_filename(filename, filename_size);
+	}
+	else
+		printf("Filename encryption disabled\n");
+	
 out:
 	if (fd != -1)
 		close(fd);