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Subject[PATCH 5/8] eCryptfs: Fix Tag 3 parsing code
Fix up the Tag 3 parsing code to handle size limits and boundaries
more explicitly.

Signed-off-by: Michael Halcrow <mhalcrow@us.ibm.com>
---
fs/ecryptfs/keystore.c | 89 +++++++++++++++++++-----------------------------
1 files changed, 35 insertions(+), 54 deletions(-)

diff --git a/fs/ecryptfs/keystore.c b/fs/ecryptfs/keystore.c
index d84292d..4caa45d 100644
--- a/fs/ecryptfs/keystore.c
+++ b/fs/ecryptfs/keystore.c
@@ -643,22 +643,30 @@ parse_tag_3_packet(struct ecryptfs_crypt_stat *crypt_stat,

(*packet_size) = 0;
(*new_auth_tok) = NULL;
-
- /* we check that:
- * one byte for the Tag 3 ID flag
- * two bytes for the body size
- * do not exceed the maximum_packet_size
+ /**
+ *This format is inspired by OpenPGP; see RFC 2440
+ * packet tag 3
+ *
+ * Tag 3 identifier (1 byte)
+ * Max Tag 3 packet size (max 3 bytes)
+ * Version (1 byte)
+ * Cipher code (1 byte)
+ * S2K specifier (1 byte)
+ * Hash identifier (1 byte)
+ * Salt (ECRYPTFS_SALT_SIZE)
+ * Hash iterations (1 byte)
+ * Encrypted key (arbitrary)
+ *
+ * (ECRYPTFS_SALT_SIZE + 7) minimum packet size
*/
- if (unlikely((*packet_size) + 3 > max_packet_size)) {
- ecryptfs_printk(KERN_ERR, "Packet size exceeds max\n");
+ if (max_packet_size < (ECRYPTFS_SALT_SIZE + 7)) {
+ printk(KERN_ERR "Max packet size too large\n");
rc = -EINVAL;
goto out;
}
-
- /* check for Tag 3 identifyer - one byte */
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);
+ printk(KERN_ERR "First byte != 0x%.2x; invalid packet\n",
+ ECRYPTFS_TAG_3_PACKET_TYPE);
rc = -EINVAL;
goto out;
}
@@ -667,56 +675,36 @@ parse_tag_3_packet(struct ecryptfs_crypt_stat *crypt_stat,
auth_tok_list_item =
kmem_cache_zalloc(ecryptfs_auth_tok_list_item_cache, GFP_KERNEL);
if (!auth_tok_list_item) {
- ecryptfs_printk(KERN_ERR, "Unable to allocate memory\n");
+ printk(KERN_ERR "Unable to allocate memory\n");
rc = -ENOMEM;
goto out;
}
(*new_auth_tok) = &auth_tok_list_item->auth_tok;
-
- /* check for body size - one to two bytes */
- 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);
+ if ((rc = parse_packet_length(&data[(*packet_size)], &body_size,
+ &length_size))) {
+ printk(KERN_WARNING "Error parsing packet length; rc = [%d]\n",
+ rc);
goto out_free;
}
- if (unlikely(body_size < (0x05 + ECRYPTFS_SALT_SIZE))) {
- ecryptfs_printk(KERN_WARNING, "Invalid body size ([%d])\n",
- body_size);
+ if (unlikely(body_size < (ECRYPTFS_SALT_SIZE + 5))) {
+ printk(KERN_WARNING "Invalid body size ([%d])\n", body_size);
rc = -EINVAL;
goto out_free;
}
(*packet_size) += length_size;
-
- /* now we know the length of the remainting Tag 3 packet size:
- * 5 fix bytes for: version string, cipher, S2K ID, hash algo,
- * number of hash iterations
- * ECRYPTFS_SALT_SIZE bytes for salt
- * body_size bytes minus the stuff above is the encrypted key size
- */
if (unlikely((*packet_size) + body_size > max_packet_size)) {
- ecryptfs_printk(KERN_ERR, "Packet size exceeds max\n");
+ 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) - one byte */
+ (body_size - (ECRYPTFS_SALT_SIZE + 5));
if (unlikely(data[(*packet_size)++] != 0x04)) {
- ecryptfs_printk(KERN_DEBUG, "Unknown version number "
- "[%d]\n", data[(*packet_size) - 1]);
+ printk(KERN_WARNING "Unknown version number [%d]\n",
+ data[(*packet_size) - 1]);
rc = -EINVAL;
goto out_free;
}
-
- /* cipher - one byte */
ecryptfs_cipher_code_to_string(crypt_stat->cipher,
(u16)data[(*packet_size)]);
/* A little extra work to differentiate among the AES key
@@ -730,33 +718,26 @@ parse_tag_3_packet(struct ecryptfs_crypt_stat *crypt_stat,
(*new_auth_tok)->session_key.encrypted_key_size;
}
ecryptfs_init_crypt_ctx(crypt_stat);
- /* S2K identifier 3 (from RFC2440) */
if (unlikely(data[(*packet_size)++] != 0x03)) {
- ecryptfs_printk(KERN_ERR, "Only S2K ID 3 is currently "
- "supported\n");
+ printk(KERN_WARNING "Only S2K ID 3 is currently supported\n");
rc = -ENOSYS;
goto out_free;
}
-
/* TODO: finish the hash mapping */
- /* hash algorithm - one byte */
switch (data[(*packet_size)++]) {
case 0x01: /* See RFC2440 for these numbers and their mappings */
/* Choose MD5 */
- /* salt - ECRYPTFS_SALT_SIZE bytes */
memcpy((*new_auth_tok)->token.password.salt,
&data[(*packet_size)], ECRYPTFS_SALT_SIZE);
(*packet_size) += ECRYPTFS_SALT_SIZE;
-
/* This conversion was taken straight from RFC2440 */
- /* number of hash iterations - one byte */
(*new_auth_tok)->token.password.hash_iterations =
((u32) 16 + (data[(*packet_size)] & 15))
<< ((data[(*packet_size)] >> 4) + 6);
(*packet_size)++;
-
- /* encrypted session key -
- * (body_size-5-ECRYPTFS_SALT_SIZE) bytes */
+ /* Friendly reminder:
+ * (*new_auth_tok)->session_key.encrypted_key_size =
+ * (body_size - (ECRYPTFS_SALT_SIZE + 5)); */
memcpy((*new_auth_tok)->session_key.encrypted_key,
&data[(*packet_size)],
(*new_auth_tok)->session_key.encrypted_key_size);
@@ -766,7 +747,7 @@ parse_tag_3_packet(struct ecryptfs_crypt_stat *crypt_stat,
~ECRYPTFS_CONTAINS_DECRYPTED_KEY;
(*new_auth_tok)->session_key.flags |=
ECRYPTFS_CONTAINS_ENCRYPTED_KEY;
- (*new_auth_tok)->token.password.hash_algo = 0x01;
+ (*new_auth_tok)->token.password.hash_algo = 0x01; /* MD5 */
break;
default:
ecryptfs_printk(KERN_ERR, "Unsupported hash algorithm: "
--
1.4.4.4
-
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