[PATCH 11/13: eCryptfs] Keystore

[Phillip Hellewell]

This is the 11th patch in a series of 13 constituting the kernel
components of the eCryptfs cryptographic filesystem.

eCryptfs keystore. Packet generation and parsing code. Authentication
token management code.

Signed-off-by: Phillip Hellewell <phillip@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Michael Halcrow <mhalcrow@xxxxxxxxxx>

---

 keystore.c | 1043 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 files changed, 1043 insertions(+)

Index: linux-2.6.17-rc3-mm1-ecryptfs/fs/ecryptfs/keystore.c
===================================================================
--- /dev/null	1970-01-01 00:00:00.000000000 +0000
+++ linux-2.6.17-rc3-mm1-ecryptfs/fs/ecryptfs/keystore.c	2006-05-12 20:00:28.000000000 -0600
@@ -0,0 +1,1043 @@
+/**
+ * eCryptfs: Linux filesystem encryption layer
+ * In-kernel key management code.  Includes functions to parse and
+ * write authentication token-related packets with the underlying
+ * file.
+ *
+ * Copyright (C) 2004-2006 International Business Machines Corp.
+ *   Author(s): Michael A. Halcrow <mhalcrow@xxxxxxxxxx>
+ *              Michael C. Thompson <mcthomps@xxxxxxxxxx>
+ *
+ * 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 (at your option) 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., 59 Temple Place - Suite 330, Boston, MA
+ * 02111-1307, USA.
+ */
+
+#include <linux/string.h>
+#include <linux/sched.h>
+#include <linux/syscalls.h>
+#include <linux/pagemap.h>
+#include <linux/key.h>
+#include <linux/random.h>
+#include <linux/crypto.h>
+#include <asm/scatterlist.h>
+#include "ecryptfs_kernel.h"
+
+/**
+ * request_key returned an error instead of a valid key address;
+ * determine the type of error, make appropriate log entries, and
+ * return an error code.
+ */
+int process_request_key_err(long err_code)
+{
+	int rc = 0;
+
+	switch (err_code) {
+	case ENOKEY:
+		ecryptfs_printk(KERN_WARNING, "No key\n");
+		rc = -ENOENT;
+		break;
+	case EKEYEXPIRED:
+		ecryptfs_printk(KERN_WARNING, "Key expired\n");
+		rc = -ETIME;
+		break;
+	case EKEYREVOKED:
+		ecryptfs_printk(KERN_WARNING, "Key revoked\n");
+		rc = -EINVAL;
+		break;
+	default:
+		ecryptfs_printk(KERN_WARNING, "Unknown error code: "
+				"[0x%.16x]\n", err_code);
+		rc = -EINVAL;
+	}
+	return rc;
+}
+
+static void wipe_auth_tok_list(struct list_head *auth_tok_list_head)
+{
+	struct list_head *walker;
+	struct ecryptfs_auth_tok_list_item *auth_tok_list_item;
+
+	walker = auth_tok_list_head->next;
+	while (walker != auth_tok_list_head) {
+		auth_tok_list_item =
+		    list_entry(walker, struct ecryptfs_auth_tok_list_item,
+			       list);
+		walker = auth_tok_list_item->list.next;
+		memset(auth_tok_list_item, 0,
+		       sizeof(struct ecryptfs_auth_tok_list_item));
+		kmem_cache_free(ecryptfs_auth_tok_list_item_cache,
+				auth_tok_list_item);
+	}
+}
+
+struct kmem_cache *ecryptfs_auth_tok_list_item_cache;
+
+/**
+ * parse_packet_length
+ * @data: Pointer to memory containing length at offset
+ * @size: This function writes the decoded size to this memory
+ *        address; zero on error
+ * @length_size: The number of bytes occupied by the encoded length
+ *
+ * Returns Zero on success
+ */
+static int parse_packet_length(unsigned char *data, int *size, int *length_size)
+{
+	int rc = 0;
+
+	(*length_size) = 0;
+	(*size) = 0;
+	if (data[0] < 192) {
+		/* One-byte length */
+		(*size) = data[0];
+		(*length_size) = 1;
+	} else if (data[0] < 224) {
+		/* Two-byte length */
+		(*size) = ((data[0] - 192) * 256);
+		(*size) += (data[1] + 192);
+		(*length_size) = 2;
+	} else if (data[0] == 255) {
+		/* Five-byte length; we're not supposed to see this */
+		ecryptfs_printk(KERN_ERR, "Five-byte packet length not "
+				"supported\n");
+		rc = -EINVAL;
+		goto out;
+	} else {
+		ecryptfs_printk(KERN_ERR, "Error parsing packet length\n");
+		rc = -EINVAL;
+		goto out;
+	}
+out:
+	return rc;
+}
+
+/**
+ * write_packet_length
+ * @dest: The byte array target into which to write the
+ *       length. Must have at least 5 bytes allocated.
+ * @size: The length to write.
+ * @packet_size_length: The number of bytes used to encode the
+ *                      packet length is written to this address.
+ *
+ * Returns zero on success; non-zero on error.
+ */
+static int write_packet_length(char *dest, int size, int *packet_size_length)
+{
+	int rc = 0;
+
+	if (size < 192) {
+		dest[0] = size;
+		(*packet_size_length) = 1;
+	} else if (size < 65536) {
+		dest[0] = (((size - 192) / 256) + 192);
+		dest[1] = ((size - 192) % 256);
+		(*packet_size_length) = 2;
+	} else {
+		rc = -EINVAL;
+		ecryptfs_printk(KERN_WARNING,
+				"Unsupported packet size: [%d]\n", size);
+	}
+	return rc;
+}
+
+/**
+ * parse_tag_3_packet
+ * @crypt_stat: The cryptographic context to modify based on packet
+ *              contents.
+ * @data: The raw bytes of the packet.
+ * @auth_tok_list: eCryptfs parses packets into authentication tokens;
+ *                 a new authentication token will be placed at the end
+ *                 of this list for this packet.
+ * @new_auth_tok: Pointer to a pointer to memory that this function
+ *                allocates; sets the memory address of the pointer to
+ *                NULL on error. This object is added to the
+ *                auth_tok_list.
+ * @packet_size: This function writes the size of the parsed packet
+ *               into this memory location; zero on error.
+ *
+ * Returns zero on success; non-zero on error.
+ */
+static int
+parse_tag_3_packet(struct ecryptfs_crypt_stat *crypt_stat,
+		   unsigned char *data, struct list_head *auth_tok_list,
+		   struct ecryptfs_auth_tok **new_auth_tok,
+		   int *packet_size, int max_packet_size)
+{
+	int rc = 0;
+	int body_size;
+	struct ecryptfs_auth_tok_list_item *auth_tok_list_item;
+	int length_size;
+
+	(*packet_size) = 0;
+	(*new_auth_tok) = NULL;
+	if (data[(*packet_size)++] != ECRYPTFS_TAG_3_PACKET_TYPE) {
+		ecryptfs_printk(KERN_ERR, "Enter w/ first byte != 0x%.2x\n",
+				ECRYPTFS_TAG_3_PACKET_TYPE);
+		rc = -EINVAL;
+		goto out;
+	}
+	if (unlikely((*packet_size) > max_packet_size)) {
+		ecryptfs_printk(KERN_ERR, "Packet size exceeds max\n");
+		rc = -EINVAL;
+		goto out;
+	}
+	/* Released: wipe_auth_tok_list called in ecryptfs_parse_packet_set or
+	 * at end of function upon failure */
+	auth_tok_list_item =
+	    kmem_cache_alloc(ecryptfs_auth_tok_list_item_cache, SLAB_KERNEL);
+	if (!auth_tok_list_item) {
+		ecryptfs_printk(KERN_ERR, "Unable to allocate memory\n");
+		rc = -ENOMEM;
+		goto out;
+	}
+	memset(auth_tok_list_item, 0,
+	       sizeof(struct ecryptfs_auth_tok_list_item));
+	(*new_auth_tok) = &auth_tok_list_item->auth_tok;
+	rc = parse_packet_length(&data[(*packet_size)], &body_size,
+				 &length_size);
+	if (rc) {
+		ecryptfs_printk(KERN_WARNING, "Error parsing packet length; "
+				"rc = [%d]\n", rc);
+		goto out_free;
+	}
+	if (body_size < (0x05 + ECRYPTFS_SALT_SIZE)) {
+		ecryptfs_printk(KERN_WARNING, "Invalid body size ([%d])\n",
+				body_size);
+		rc = -EINVAL;
+		goto out_free;
+	}
+	(*packet_size) += length_size;
+	if (unlikely((*packet_size) > max_packet_size)) {
+		ecryptfs_printk(KERN_ERR, "Packet size exceeds max\n");
+		rc = -EINVAL;
+		goto out_free;
+	}
+	/* There are 5 characters of additional information in the
+	 * packet */
+	(*new_auth_tok)->session_key.encrypted_key_size =
+		body_size - (0x05 + ECRYPTFS_SALT_SIZE);
+	ecryptfs_printk(KERN_DEBUG, "Encrypted key size = [%d]\n",
+			(*new_auth_tok)->session_key.encrypted_key_size);
+	/* Version 4 (from RFC2440) */
+	if (data[(*packet_size)++] != 0x04) {
+		ecryptfs_printk(KERN_DEBUG, "Unknown version number "
+				"[%d]\n", data[(*packet_size) - 1]);
+		rc = -EINVAL;
+		goto out_free;
+	}
+	if (unlikely((*packet_size) > max_packet_size)) {
+		ecryptfs_printk(KERN_ERR, "Packet size exceeds max\n");
+		rc = -EINVAL;
+		goto out;
+	}
+	ecryptfs_cipher_code_to_string(crypt_stat->cipher,
+				       (u16)data[(*packet_size)]);
+	/* A little extra work to differentiate among the AES key
+	 * sizes; see RFC2440 */
+	switch(data[(*packet_size)++]) {
+	case 0x07:
+		crypt_stat->key_size_bits = 128;
+		break;
+	case 0x08:
+		crypt_stat->key_size_bits = 192;
+		break;
+	case 0x09:
+		crypt_stat->key_size_bits = 256;
+		break;
+	}
+	if (unlikely((*packet_size) > max_packet_size)) {
+		ecryptfs_printk(KERN_ERR, "Packet size exceeds max\n");
+		rc = -EINVAL;
+		goto out_free;
+	}
+	ecryptfs_init_crypt_ctx(crypt_stat);
+	/* S2K identifier 3 (from RFC2440) */
+	if (data[(*packet_size)++] != 0x03) {
+		ecryptfs_printk(KERN_ERR, "Only S2K ID 3 is currently "
+				"supported\n");
+		rc = -ENOSYS;
+		goto out_free;
+	}
+	if (unlikely((*packet_size) > max_packet_size)) {
+		ecryptfs_printk(KERN_ERR, "Packet size exceeds max\n");
+		rc = -EINVAL;
+		goto out_free;
+	}
+	/* TODO: finish the hash mapping */
+	switch (data[(*packet_size)++]) {
+	case 0x01: /* See RFC2440 for these numbers and their mappings */
+		/* Choose MD5 */
+		memcpy((*new_auth_tok)->token.password.salt,
+		       &data[(*packet_size)], ECRYPTFS_SALT_SIZE);
+		(*packet_size) += ECRYPTFS_SALT_SIZE;
+		if (unlikely((*packet_size) > max_packet_size)) {
+			ecryptfs_printk(KERN_ERR,
+					"Packet size exceeds max\n");
+			rc = -EINVAL;
+			goto out_free;
+		}
+		/* This conversion was taken straight from RFC2440 */
+		(*new_auth_tok)->token.password.hash_iterations =
+			((u32) 16 + (data[(*packet_size)] & 15))
+				<< ((data[(*packet_size)] >> 4) + 6);
+		(*packet_size)++;
+		if (unlikely((*packet_size) > max_packet_size)) {
+			ecryptfs_printk(KERN_ERR,
+					"Packet size exceeds max\n");
+			rc = -EINVAL;
+			goto out_free;
+		}
+		memcpy((*new_auth_tok)->session_key.encrypted_key,
+		       &data[(*packet_size)],
+		       (*new_auth_tok)->session_key.encrypted_key_size);
+		(*packet_size) +=
+			(*new_auth_tok)->session_key.encrypted_key_size;
+		if (unlikely((*packet_size) > max_packet_size)) {
+			ecryptfs_printk(KERN_ERR,
+					"Packet size exceeds max\n");
+			rc = -EINVAL;
+			goto out_free;
+		}
+		(*new_auth_tok)->session_key.flags &=
+			~ECRYPTFS_CONTAINS_DECRYPTED_KEY;
+		(*new_auth_tok)->session_key.flags |=
+			ECRYPTFS_CONTAINS_ENCRYPTED_KEY;
+		(*new_auth_tok)->token.password.hash_algo = 0x01;
+		break;
+	default:
+		ecryptfs_printk(KERN_ERR, "Unsupported hash algorithm: "
+				"[%d]\n", data[(*packet_size) - 1]);
+		rc = -ENOSYS;
+		goto out_free;
+	}
+	if (unlikely((*packet_size) > max_packet_size)) {
+		ecryptfs_printk(KERN_ERR, "Packet size exceeds max\n");
+		rc = -EINVAL;
+		goto out;
+	}
+	/* TODO: Use the keyring */
+	(*new_auth_tok)->uid = current->uid;
+	ECRYPTFS_SET_FLAG((*new_auth_tok)->flags, ECRYPTFS_PASSWORD);
+	/* TODO: Parametarize; we might actually want userspace to
+	 * decrypt the session key. */
+	ECRYPTFS_CLEAR_FLAG((*new_auth_tok)->session_key.flags,
+			    ECRYPTFS_USERSPACE_SHOULD_TRY_TO_DECRYPT);
+	ECRYPTFS_CLEAR_FLAG((*new_auth_tok)->session_key.flags,
+			    ECRYPTFS_USERSPACE_SHOULD_TRY_TO_ENCRYPT);
+	list_add(&auth_tok_list_item->list, auth_tok_list);
+	goto out;
+out_free:
+	(*new_auth_tok) = NULL;
+	memset(auth_tok_list_item, 0,
+	       sizeof(struct ecryptfs_auth_tok_list_item));
+	kmem_cache_free(ecryptfs_auth_tok_list_item_cache,
+			auth_tok_list_item);
+out:
+	if (rc)
+		(*packet_size) = 0;
+	return rc;
+}
+
+/**
+ * parse_tag_11_packet
+ * @data: The raw bytes of the packet
+ * @contents: This function writes the data contents of the literal
+ *            packet into this memory location
+ * @max_contents_bytes: The maximum number of bytes that this function
+ *                      is allowed to write into contents
+ * @tag_11_contents_size: This function writes the size of the parsed
+ *                        contents into this memory location; zero on
+ *                        error
+ * @packet_size: This function writes the size of the parsed packet
+ *               into this memory location; zero on error
+ *
+ * Returns zero on success; non-zero on error.
+ */
+static int
+parse_tag_11_packet(unsigned char *data, unsigned char *contents,
+		    int max_contents_bytes, int *tag_11_contents_size,
+		    int *packet_size, int max_packet_size)
+{
+	int rc = 0;
+	int body_size;
+	int length_size;
+
+	(*packet_size) = 0;
+	(*tag_11_contents_size) = 0;
+	if (data[(*packet_size)++] != ECRYPTFS_TAG_11_PACKET_TYPE) {
+		ecryptfs_printk(KERN_WARNING,
+				"Invalid tag 11 packet format\n");
+		rc = -EINVAL;
+		goto out;
+	}
+	if (unlikely((*packet_size) > max_packet_size)) {
+		ecryptfs_printk(KERN_ERR, "Packet size exceeds max\n");
+		rc = -EINVAL;
+		goto out;
+	}
+	rc = parse_packet_length(&data[(*packet_size)], &body_size,
+				 &length_size);
+	if (rc) {
+		ecryptfs_printk(KERN_WARNING,
+				"Invalid tag 11 packet format\n");
+		goto out;
+	}
+	(*packet_size) += length_size;
+	if (unlikely((*packet_size) > max_packet_size)) {
+		ecryptfs_printk(KERN_ERR, "Packet size exceeds max\n");
+		rc = -EINVAL;
+		goto out;
+	}
+	/* We have 13 bytes of surrounding packet values */
+	(*tag_11_contents_size) = (body_size - 13);
+	if ((*tag_11_contents_size) > max_contents_bytes) {
+		rc = -ENOMEM;
+		ecryptfs_printk(KERN_WARNING, "Not enough space allocated "
+				"in contents to copy entire contents of tag 11 "
+				"packet\n");
+		goto out;
+	}
+	if (data[(*packet_size)++] != 0x62) {
+		ecryptfs_printk(KERN_WARNING, "Unrecognizable packet\n");
+		rc = -EINVAL;
+		goto out;
+	}
+	if (unlikely((*packet_size) > max_packet_size)) {
+		ecryptfs_printk(KERN_ERR, "Packet size exceeds max\n");
+		rc = -EINVAL;
+		goto out;
+	}
+	if (data[(*packet_size)++] != 0x08) {
+		ecryptfs_printk(KERN_WARNING, "Unrecognizable packet\n");
+		rc = -EINVAL;
+		goto out;
+	}
+	if (unlikely((*packet_size) > max_packet_size)) {
+		ecryptfs_printk(KERN_ERR, "Packet size exceeds max\n");
+		rc = -EINVAL;
+		goto out;
+	}
+	(*packet_size) += 12; /* We don't care about the filename or
+			       * the timestamp */
+	if (unlikely((*packet_size) > max_packet_size)) {
+		ecryptfs_printk(KERN_ERR, "Packet size exceeds max\n");
+		rc = -EINVAL;
+		goto out;
+	}
+	memcpy(contents, &data[(*packet_size)], (*tag_11_contents_size));
+	(*packet_size) += (*tag_11_contents_size);
+	if (unlikely((*packet_size) > max_packet_size)) {
+		ecryptfs_printk(KERN_ERR, "Packet size exceeds max\n");
+		rc = -EINVAL;
+		goto out;
+	}
+out:
+	if (rc) {
+		(*packet_size) = 0;
+		(*tag_11_contents_size) = 0;
+	}
+	return rc;
+}
+
+/**
+ * decrypt_session_key - Decrypt the session key with the given auth_tok.
+ *
+ * Returns Zero on success; non-zero error otherwise.
+ */
+static int decrypt_session_key(struct ecryptfs_auth_tok *auth_tok,
+			       struct ecryptfs_crypt_stat *crypt_stat)
+{
+	int rc = 0;
+	struct ecryptfs_password *password_s_ptr;
+	struct crypto_tfm *tfm = NULL;
+	struct scatterlist src_sg[2], dst_sg[2];
+	/* TODO: Use virt_to_scatterlist for these */
+	char *encrypted_session_key;
+	char *session_key;
+
+	password_s_ptr = &auth_tok->token.password;
+	if (ECRYPTFS_CHECK_FLAG(password_s_ptr->flags,
+				ECRYPTFS_SESSION_KEY_ENCRYPTION_KEY_SET))
+		ecryptfs_printk(KERN_DEBUG, "Session key encryption key "
+				"set; skipping key generation\n");
+	ecryptfs_printk(KERN_DEBUG, "Session key encryption key (size [%d])"
+			":\n",
+			password_s_ptr->session_key_encryption_key_bytes);
+	if (ecryptfs_verbosity > 0)
+		ecryptfs_dump_hex(password_s_ptr->session_key_encryption_key,
+				  password_s_ptr->
+				  session_key_encryption_key_bytes);
+	tfm = crypto_alloc_tfm(crypt_stat->cipher, 0);
+	if (!tfm) {
+		ecryptfs_printk(KERN_ERR, "Error allocating crypto "
+				"context\n");
+		rc = -ENOMEM;
+		goto out;
+	}
+	crypto_cipher_setkey(tfm, password_s_ptr->session_key_encryption_key,
+			     password_s_ptr->session_key_encryption_key_bytes);
+	/* TODO: virt_to_scatterlist */
+	encrypted_session_key = (char *)__get_free_page(GFP_KERNEL);
+	if (!encrypted_session_key) {
+		ecryptfs_printk(KERN_ERR, "Out of memory\n");
+		rc = -ENOMEM;
+		goto out_free_tfm;
+	}
+	session_key = (char *)__get_free_page(GFP_KERNEL);
+	if (!session_key) {
+		kfree(encrypted_session_key);
+		ecryptfs_printk(KERN_ERR, "Out of memory\n");
+		rc = -ENOMEM;
+		goto out_free_tfm;
+	}
+	memcpy(encrypted_session_key, auth_tok->session_key.encrypted_key,
+	       auth_tok->session_key.encrypted_key_size);
+	src_sg[0].page = virt_to_page(encrypted_session_key);
+	src_sg[0].offset = 0;
+	ASSERT(auth_tok->session_key.encrypted_key_size < PAGE_CACHE_SIZE);
+	src_sg[0].length = auth_tok->session_key.encrypted_key_size;
+	dst_sg[0].page = virt_to_page(session_key);
+	dst_sg[0].offset = 0;
+	auth_tok->session_key.decrypted_key_size =
+	    auth_tok->session_key.encrypted_key_size;
+	dst_sg[0].length = auth_tok->session_key.encrypted_key_size;
+	/* TODO: Handle error condition */
+	crypto_cipher_decrypt(tfm, dst_sg, src_sg,
+			      auth_tok->session_key.encrypted_key_size);
+	auth_tok->session_key.decrypted_key_size =
+	    auth_tok->session_key.encrypted_key_size;
+	memcpy(auth_tok->session_key.decrypted_key, session_key,
+	       auth_tok->session_key.decrypted_key_size);
+	auth_tok->session_key.flags |= ECRYPTFS_CONTAINS_DECRYPTED_KEY;
+	memcpy(crypt_stat->key, auth_tok->session_key.decrypted_key,
+	       auth_tok->session_key.decrypted_key_size);
+	ECRYPTFS_SET_FLAG(crypt_stat->flags, ECRYPTFS_KEY_VALID);
+	crypt_stat->key_size_bits =
+	    auth_tok->session_key.decrypted_key_size * 8;
+	ecryptfs_printk(KERN_DEBUG, "Decrypted session key:\n");
+	if (ecryptfs_verbosity > 0)
+		ecryptfs_dump_hex(crypt_stat->key,
+				  crypt_stat->key_size_bits / 8);
+	memset(encrypted_session_key, 0, PAGE_CACHE_SIZE);
+	free_page((unsigned long)encrypted_session_key);
+	memset(session_key, 0, PAGE_CACHE_SIZE);
+	free_page((unsigned long)session_key);
+out_free_tfm:
+	crypto_free_tfm(tfm);
+out:
+	return rc;
+}
+
+/**
+ * ecryptfs_parse_packet_set
+ * @dest: The header page in memory
+ * @version: Version of file format, to guide parsing behavior
+ *
+ * Get crypt_stat to have the file's session key if the requisite key
+ * is available to decrypt the session key.
+ *
+ * Returns Zero if a valid authentication token was retrieved and
+ * processed; negative value for file not encrypted or for error
+ * conditions.
+ */
+int ecryptfs_parse_packet_set(struct ecryptfs_crypt_stat *crypt_stat,
+			      unsigned char *src,
+			      struct dentry *ecryptfs_dentry)
+{
+	int i = 0;
+	int rc = 0;
+	int found_auth_tok = 0;
+	int next_packet_is_auth_tok_packet;
+	char sig[ECRYPTFS_SIG_SIZE_HEX];
+	struct list_head auth_tok_list;
+	struct list_head *walker;
+	struct ecryptfs_auth_tok *chosen_auth_tok = NULL;
+	struct ecryptfs_mount_crypt_stat *mount_crypt_stat =
+		&ecryptfs_superblock_to_private(
+			ecryptfs_dentry->d_sb)->mount_crypt_stat;
+	struct ecryptfs_auth_tok *candidate_auth_tok = NULL;
+	int packet_size;
+	struct ecryptfs_auth_tok *new_auth_tok;
+	unsigned char sig_tmp_space[ECRYPTFS_SIG_SIZE];
+	int tag_11_contents_size;
+	int tag_11_packet_size;
+
+	INIT_LIST_HEAD(&auth_tok_list);
+	/* Parse the header to find as many packets as we can, these will be
+	 * added the our &auth_tok_list */
+	next_packet_is_auth_tok_packet = 1;
+	while (next_packet_is_auth_tok_packet) {
+		int max_packet_size;
+
+		max_packet_size = ((PAGE_CACHE_SIZE - 8) - i);
+		switch (src[i]) {
+		case ECRYPTFS_TAG_3_PACKET_TYPE:
+			rc = parse_tag_3_packet(crypt_stat,
+						(unsigned char *)&src[i],
+						&auth_tok_list, &new_auth_tok,
+						&packet_size, max_packet_size);
+			if (rc) {
+				ecryptfs_printk(KERN_ERR, "Error parsing "
+						"tag 3 packet\n");
+				rc = -EIO;
+				goto out_wipe_list;
+			}
+			i += packet_size;
+			rc = parse_tag_11_packet((unsigned char *)&src[i],
+						 sig_tmp_space,
+						 ECRYPTFS_SIG_SIZE,
+						 &tag_11_contents_size,
+						 &tag_11_packet_size,
+						 max_packet_size);
+			if (rc) {
+				ecryptfs_printk(KERN_ERR, "No valid "
+						"(ecryptfs-specific) literal "
+						"packet containing "
+						"authentication token "
+						"signature found after "
+						"tag 3 packet\n");
+				rc = -EIO;
+				goto out_wipe_list;
+			}
+			i += tag_11_packet_size;
+			if (ECRYPTFS_SIG_SIZE != tag_11_contents_size) {
+				ecryptfs_printk(KERN_ERR, "Expected "
+						"signature of size [%d]; "
+						"read size [%d]\n",
+						ECRYPTFS_SIG_SIZE,
+						tag_11_contents_size);
+				rc = -EIO;
+				goto out_wipe_list;
+			}
+			ecryptfs_to_hex(new_auth_tok->token.password.signature,
+					sig_tmp_space, tag_11_contents_size);
+			new_auth_tok->token.password.signature[
+				ECRYPTFS_PASSWORD_SIG_SIZE] = '\0';
+			ECRYPTFS_SET_FLAG(crypt_stat->flags,
+					  ECRYPTFS_ENCRYPTED);
+			break;
+		case ECRYPTFS_TAG_11_PACKET_TYPE:
+			ecryptfs_printk(KERN_WARNING, "Invalid packet set "
+					"(Tag 11 not allowed by itself)\n");
+			rc = -EIO;
+			goto out_wipe_list;
+			break;
+		default:
+			ecryptfs_printk(KERN_DEBUG, "No packet at offset "
+					"[%d] of the file header; hex value of "
+					"character is [0x%.2x]\n", i, src[i]);
+			next_packet_is_auth_tok_packet = 0;
+		}
+	}
+	if (list_empty(&auth_tok_list)) {
+		rc = -EINVAL; /* Do not support non-encrypted files in
+			       * the 0.1 release */
+		goto out;
+	}
+	/* If we have a global auth tok, then we should try to use
+	 * it */
+	if (mount_crypt_stat->global_auth_tok) {
+		memcpy(sig, mount_crypt_stat->global_auth_tok_sig,
+		       ECRYPTFS_SIG_SIZE_HEX);
+		chosen_auth_tok = mount_crypt_stat->global_auth_tok;
+	} else
+		BUG(); /* We should always have a global auth tok in
+			* the 0.1 release */
+	/* Scan list to see if our chosen_auth_tok works */
+	list_for_each(walker, &auth_tok_list) {
+		struct ecryptfs_auth_tok_list_item *auth_tok_list_item;
+		auth_tok_list_item =
+		    list_entry(walker, struct ecryptfs_auth_tok_list_item,
+			       list);
+		candidate_auth_tok = &auth_tok_list_item->auth_tok;
+		if (unlikely(ecryptfs_verbosity > 0)) {
+			ecryptfs_printk(KERN_DEBUG,
+					"Considering cadidate auth tok:\n");
+			ecryptfs_dump_auth_tok(candidate_auth_tok);
+		}
+		/* TODO: Replace ECRYPTFS_SIG_SIZE_HEX w/ dynamic value */
+		if ((ECRYPTFS_CHECK_FLAG(candidate_auth_tok->flags,
+					 ECRYPTFS_PASSWORD))
+		    && !strncmp(candidate_auth_tok->token.password.signature,
+				sig, ECRYPTFS_SIG_SIZE_HEX)) {
+			found_auth_tok = 1;
+			goto leave_list;
+			/* TODO: Transfer the common salt into the
+			 * crypt_stat salt */
+		}
+	}
+leave_list:
+	if (!found_auth_tok) {
+		ecryptfs_printk(KERN_ERR, "Could not find authentication "
+				"token on temporary list for sig [%.*s]\n",
+				ECRYPTFS_SIG_SIZE_HEX, sig);
+		rc = -EIO;
+		goto out_wipe_list;
+	} else {
+		memcpy(&(candidate_auth_tok->token.password),
+		       &(chosen_auth_tok->token.password),
+		       sizeof(struct ecryptfs_password));
+		rc = decrypt_session_key(candidate_auth_tok, crypt_stat);
+		if (rc) {
+			ecryptfs_printk(KERN_ERR, "Error decrypting the "
+					"session key\n");
+			goto out_wipe_list;
+		}
+		rc = ecryptfs_compute_root_iv(crypt_stat);
+		if (rc) {
+			ecryptfs_printk(KERN_ERR, "Error computing "
+					"the root IV\n");
+			goto out_wipe_list;
+		}
+	}
+	rc = ecryptfs_init_crypt_ctx(crypt_stat);
+	if (rc) {
+		ecryptfs_printk(KERN_ERR, "Error initializing crypto "
+				"context for cipher [%s]; rc = [%d]\n",
+				crypt_stat->cipher, rc);
+	}
+out_wipe_list:
+	wipe_auth_tok_list(&auth_tok_list);
+out:
+	return rc;
+}
+
+/**
+ * write_tag_11_packet
+ * @dest: Target into which Tag 11 packet is to be written
+ * @max: Maximum packet length
+ * @contents: Byte array of contents to copy in
+ * @contents_length: Number of bytes in contents
+ * @packet_length: Length of the Tag 11 packet written; zero on error
+ *
+ * Returns zero on success; non-zero on error.
+ */
+int
+write_tag_11_packet(char *dest, int max, char *contents, int contents_length,
+		    int *packet_length)
+{
+	int rc = 0;
+	int packet_size_length;
+
+	(*packet_length) = 0;
+	if ((13 + contents_length) > max) {
+		rc = -EINVAL;
+		ecryptfs_printk(KERN_ERR, "Packet length larger than "
+				"maximum allowable\n");
+		goto out;
+	}
+	/* General packet header */
+	/* Packet tag */
+	dest[(*packet_length)++] = ECRYPTFS_TAG_11_PACKET_TYPE;
+	/* Packet length */
+	rc = write_packet_length(&dest[(*packet_length)],
+				 (13 + contents_length), &packet_size_length);
+	if (rc) {
+		ecryptfs_printk(KERN_ERR, "Error generating tag 11 packet "
+				"header; cannot generate packet length\n");
+		goto out;
+	}
+	(*packet_length) += packet_size_length;
+	/* Tag 11 specific */
+	/* One-octet field that describes how the data is formatted */
+	dest[(*packet_length)++] = 0x62; /* binary data */
+	/* One-octet filename length followed by filename */
+	dest[(*packet_length)++] = 8;
+	memcpy(&dest[(*packet_length)], "_CONSOLE", 8);
+	(*packet_length) += 8;
+	/* Four-octet number indicating modification date */
+	memset(&dest[(*packet_length)], 0x00, 4);
+	(*packet_length) += 4;
+	/* Remainder is literal data */
+	memcpy(&dest[(*packet_length)], contents, contents_length);
+	(*packet_length) += contents_length;
+ out:
+	if (rc)
+		(*packet_length) = 0;
+	return rc;
+}
+
+/**
+ * write_tag_3_packet
+ * @dest: Buffer into which to write the packet
+ * @max: Maximum number of bytes that can be writtn
+ * @packet_size: This function will write the number of bytes that end
+ *               up constituting the packet; set to zero on error
+ *
+ * Returns zero on success; non-zero on error.
+ */
+static int
+write_tag_3_packet(char *dest, int max, struct ecryptfs_auth_tok *auth_tok,
+		   struct ecryptfs_crypt_stat *crypt_stat,
+		   struct ecryptfs_key_record *key_rec, int *packet_size)
+{
+	int rc = 0;
+
+	int i;
+	int signature_is_valid = 0;
+	int encrypted_session_key_valid = 0;
+	char session_key_encryption_key[ECRYPTFS_MAX_KEY_BYTES];
+	struct scatterlist dest_sg[2];
+	struct scatterlist src_sg[2];
+	struct crypto_tfm *tfm = NULL;
+	int key_rec_size;
+	int packet_size_length;
+	int cipher_code;
+
+	(*packet_size) = 0;
+	/* Check for a valid signature on the auth_tok */
+	for (i = 0; i < ECRYPTFS_SIG_SIZE_HEX; i++)
+		signature_is_valid |= auth_tok->token.password.signature[i];
+	if (!signature_is_valid)
+		BUG();
+	ecryptfs_from_hex((*key_rec).sig, auth_tok->token.password.signature,
+			  ECRYPTFS_SIG_SIZE);
+	(*key_rec).enc_key_size_bits = crypt_stat->key_size_bits;
+	encrypted_session_key_valid = 0;
+	if (auth_tok->session_key.encrypted_key_size == 0)
+		auth_tok->session_key.encrypted_key_size =
+		    ECRYPTFS_MAX_ENCRYPTED_KEY_BYTES;
+	for (i = 0; i < auth_tok->session_key.encrypted_key_size; i++)
+		encrypted_session_key_valid |=
+		    auth_tok->session_key.encrypted_key[i];
+	if (auth_tok->session_key.encrypted_key_size == 0) {
+		ecryptfs_printk(KERN_WARNING, "auth_tok->session_key."
+				"encrypted_key_size == 0");
+		auth_tok->session_key.encrypted_key_size =
+		    ECRYPTFS_DEFAULT_KEY_BYTES;
+	}
+	if (encrypted_session_key_valid) {
+		memcpy((*key_rec).enc_key,
+		       auth_tok->session_key.encrypted_key,
+		       auth_tok->session_key.encrypted_key_size);
+		goto encrypted_session_key_set;
+	}
+	if (ECRYPTFS_CHECK_FLAG(auth_tok->token.password.flags,
+				ECRYPTFS_SESSION_KEY_ENCRYPTION_KEY_SET)) {
+		ecryptfs_printk(KERN_DEBUG, "Using previously generated "
+				"session key encryption key of size [%d]\n",
+				auth_tok->token.password.
+				session_key_encryption_key_bytes);
+		memcpy(session_key_encryption_key,
+		       auth_tok->token.password.session_key_encryption_key,
+		       auth_tok->token.password.
+		       session_key_encryption_key_bytes);
+		ecryptfs_printk(KERN_DEBUG,
+				"Cached session key " "encryption key: \n");
+		if (ecryptfs_verbosity > 0)
+			ecryptfs_dump_hex(session_key_encryption_key, 16);
+	}
+	if (unlikely(ecryptfs_verbosity > 0)) {
+		ecryptfs_printk(KERN_DEBUG, "Session key encryption key:"
+				"\n");
+		ecryptfs_dump_hex(session_key_encryption_key, 16);
+	}
+	/* Encrypt the key with the key encryption key */
+	/* Set up the scatterlists */
+	rc = virt_to_scatterlist(crypt_stat->key,
+				 crypt_stat->key_size_bits / 8, src_sg, 2);
+	if (!rc) {
+		ecryptfs_printk(KERN_ERR, "Error generating scatterlist "
+				"for crypt_stat session key\n");
+		rc = -ENOMEM;
+		goto out;
+	}
+	rc = virt_to_scatterlist((*key_rec).enc_key,
+				 (*key_rec).enc_key_size_bits / 8, dest_sg, 2);
+	if (!rc) {
+		ecryptfs_printk(KERN_ERR, "Error generating scatterlist "
+				"for crypt_stat encrypted session key\n");
+		rc = -ENOMEM;
+		goto out;
+	}
+	if ((tfm = crypto_alloc_tfm(crypt_stat->cipher, 0)) == NULL) {
+		ecryptfs_printk(KERN_ERR, "Could not initialize crypto "
+				"context for cipher [%s]\n",
+				crypt_stat->cipher);
+		rc = -EINVAL;
+		goto out;
+	}
+	rc = crypto_cipher_setkey(tfm, session_key_encryption_key,
+				  ECRYPTFS_DEFAULT_KEY_BYTES);
+	if (rc < 0) {
+		ecryptfs_printk(KERN_ERR, "Error setting key for crypto "
+				"context\n");
+		goto out;
+	}
+	rc = 0;
+	ecryptfs_printk(KERN_DEBUG, "Encrypting [%d] bytes of the key\n",
+			crypt_stat->key_size_bits / 8);
+	crypto_cipher_encrypt(tfm, dest_sg, src_sg,
+			      crypt_stat->key_size_bits / 8);
+	ecryptfs_printk(KERN_DEBUG, "This should be the encrypted key:\n");
+	if (ecryptfs_verbosity > 0)
+		ecryptfs_dump_hex((*key_rec).enc_key,
+				  (*key_rec).enc_key_size_bits / 8);
+encrypted_session_key_set:
+	/* Now we have a valid key_rec.  Append it to the
+	 * key_rec set. */
+	key_rec_size = (sizeof(struct ecryptfs_key_record)
+			- ECRYPTFS_MAX_KEY_BYTES
+			+ ((*key_rec).enc_key_size_bits / 8) );
+	/* TODO: Include a packet size limit as a parameter to this
+	 * function once we have multi-packet headers (for versions
+	 * later than 0.1 */
+	if (key_rec_size >= ECRYPTFS_MAX_KEYSET_SIZE) {
+		ecryptfs_printk(KERN_ERR, "Keyset too large\n");
+		rc = -EINVAL;
+		goto out;
+	}
+	/* TODO: Packet size limit */
+	/* We have 5 bytes of surrounding packet data */
+	if ((0x05 + ECRYPTFS_SALT_SIZE
+	     + ((*key_rec).enc_key_size_bits / 8)) >= PAGE_CACHE_SIZE) {
+		ecryptfs_printk(KERN_ERR, "Authentication token is too "
+				"large\n");
+		rc = -EINVAL;
+		goto out;
+	}
+	/* This format is inspired by OpenPGP; see RFC 2440
+	 * packet tag 3 */
+	dest[(*packet_size)++] = ECRYPTFS_TAG_3_PACKET_TYPE;
+	/* ver+cipher+s2k+hash+salt+iter+enc_key */
+	rc = write_packet_length(&dest[(*packet_size)],
+				 (0x05 + ECRYPTFS_SALT_SIZE
+				  + ((*key_rec).enc_key_size_bits / 8)),
+				 &packet_size_length);
+	if (rc) {
+		ecryptfs_printk(KERN_ERR, "Error generating tag 3 packet "
+				"header; cannot generate packet length\n");
+		goto out;
+	}
+	(*packet_size) += packet_size_length;
+	dest[(*packet_size)++] = 0x04; /* version 4 */
+	cipher_code = ecryptfs_code_for_cipher_string(crypt_stat->cipher);
+	if (cipher_code == 0) {
+		ecryptfs_printk(KERN_WARNING, "Unable to generate code for "
+				"cipher [%s]\n", crypt_stat->cipher);
+		rc = -EINVAL;
+		goto out;
+	}
+	/* If it is AES, we need to get more specific. */
+	if (cipher_code == 0x07) {
+		switch (crypt_stat->key_size_bits) {
+		case 128:
+			break;
+		case 192:
+			cipher_code = 0x08;	/* AES-192 */
+			break;
+		case 256:
+			cipher_code = 0x09;	/* AES-256 */
+			break;
+		default:
+			rc = -EINVAL;
+			ecryptfs_printk(KERN_WARNING, "Unsupported AES key "
+					"size: [%d]\n",
+					crypt_stat->key_size_bits);
+			goto out;
+		}		
+	}
+	dest[(*packet_size)++] = cipher_code;
+	dest[(*packet_size)++] = 0x03;	/* S2K */
+	dest[(*packet_size)++] = 0x01;	/* MD5 (TODO: parameterize) */
+	memcpy(&dest[(*packet_size)], auth_tok->token.password.salt,
+	       ECRYPTFS_SALT_SIZE);
+	(*packet_size) += ECRYPTFS_SALT_SIZE;	/* salt */
+	dest[(*packet_size)++] = 0x60;	/* hash iterations (65536) */
+	memcpy(&dest[(*packet_size)], (*key_rec).enc_key,
+	       (*key_rec).enc_key_size_bits / 8);
+	(*packet_size) += ((*key_rec).enc_key_size_bits / 8);
+out:
+	if (tfm)
+		crypto_free_tfm(tfm);
+	if (rc)
+		(*packet_size) = 0;
+	return rc;
+}
+
+/**
+ * ecryptfs_generate_key_packet_set
+ * @dest: Virtual address from which to write the key record set
+ * @crypt_stat: The cryptographic context from which the
+ *              authentication tokens will be retrieved
+ * @ecryptfs_dentry: The dentry, used to retrieve the mount crypt stat
+ *                   for the global parameters
+ * @len: The amount written
+ *
+ * Generates a key packet set and writes it to the virtual address
+ * passed in.
+ *
+ * Returns zero on success; non-zero on error.
+ */
+int
+ecryptfs_generate_key_packet_set(char *dest_base,
+				 struct ecryptfs_crypt_stat *crypt_stat,
+				 struct dentry *ecryptfs_dentry, int *len)
+{
+	int rc = 0;
+	struct ecryptfs_auth_tok *auth_tok;
+	struct ecryptfs_mount_crypt_stat *mount_crypt_stat =
+		&ecryptfs_superblock_to_private(
+			ecryptfs_dentry->d_sb)->mount_crypt_stat;
+	int written;
+	struct ecryptfs_key_record key_rec;
+
+	(*len) = 0;
+	if (mount_crypt_stat->global_auth_tok) {
+		auth_tok = mount_crypt_stat->global_auth_tok;
+		if (ECRYPTFS_CHECK_FLAG(auth_tok->flags, ECRYPTFS_PASSWORD)) {
+			rc = write_tag_3_packet((dest_base + (*len)),
+						PAGE_CACHE_SIZE, auth_tok,
+						crypt_stat, &key_rec,
+						&written);
+			if (rc) {
+				ecryptfs_printk(KERN_WARNING, "Error "
+						"writing tag 3 packet\n");
+				goto out;
+			}
+			(*len) += written;
+			/* Write auth tok signature packet */
+			rc = write_tag_11_packet(
+				(dest_base + (*len)),
+				(PAGE_CACHE_SIZE - (*len)),
+				key_rec.sig, ECRYPTFS_SIG_SIZE, &written);
+			if (rc) {
+				ecryptfs_printk(KERN_ERR, "Error writing "
+						"auth tok signature packet\n");
+				goto out;
+			}
+			(*len) += written;
+		} else {
+			ecryptfs_printk(KERN_WARNING, "Unsupported "
+					"authentication token type\n");
+			rc = -EINVAL;
+			goto out;
+		}
+		if (rc) {
+			ecryptfs_printk(KERN_WARNING, "Error writing "
+					"authentication token packet with sig "
+					"= [%s]\n",
+					mount_crypt_stat->global_auth_tok_sig);
+			rc = -EIO;
+			goto out;
+		}
+	} else
+		BUG();
+	dest_base[(*len)] = 0x00;
+out:
+	if (rc)
+		(*len) = 0;
+	return rc;
+}
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