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>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/fs/ecryptfs/keystore.c b/fs/ecryptfs/keystore.c
index f7debe6961d10058a608245bc46ee8fed99003cd..72086141a6e8315eb67a03a04d8bd76bf6765555 100644 (file)
--- 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: "