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>

1 files changed, 35 insertions, 54 deletions

diff --git a/fs/ecryptfs/keystore.c b/fs/ecryptfs/keystore.c
index f7debe6961d1..72086141a6e8 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: "