eCryptfs: Replace miscdev read/write magic numbers

ecryptfs_miscdev_read() and ecryptfs_miscdev_write() contained many
magic numbers for specifying packet header field sizes and offsets. This
patch defines those values and replaces the magic values.

Signed-off-by: Tyler Hicks <tyhicks@canonical.com>

3 files changed, 55 insertions, 41 deletions

diff --git a/fs/ecryptfs/ecryptfs_kernel.h b/fs/ecryptfs/ecryptfs_kernel.h
index a9f29b12fbf2..a2362df58ae8 100644
--- a/fs/ecryptfs/ecryptfs_kernel.h
+++ b/fs/ecryptfs/ecryptfs_kernel.h
@@ -151,6 +151,11 @@ ecryptfs_get_key_payload_data(struct key *key)
                                           * dentry name */
 #define ECRYPTFS_TAG_73_PACKET_TYPE 0x49 /* FEK-encrypted filename as
                                           * metadata */
+#define ECRYPTFS_MIN_PKT_LEN_SIZE 1 /* Min size to specify packet length */
+#define ECRYPTFS_MAX_PKT_LEN_SIZE 2 /* Pass at least this many bytes to
+                                     * ecryptfs_parse_packet_length() and
+                                     * ecryptfs_write_packet_length()
+                                     */
 /* Constraint: ECRYPTFS_FILENAME_MIN_RANDOM_PREPEND_BYTES >=
  * ECRYPTFS_MAX_IV_BYTES */
 #define ECRYPTFS_FILENAME_MIN_RANDOM_PREPEND_BYTES 16
diff --git a/fs/ecryptfs/keystore.c b/fs/ecryptfs/keystore.c
index ac1ad48c2376..8e3b943e330f 100644
--- a/fs/ecryptfs/keystore.c
+++ b/fs/ecryptfs/keystore.c
@@ -109,7 +109,7 @@ int ecryptfs_parse_packet_length(unsigned char *data, size_t *size,
                 (*size) += ((unsigned char)(data[1]) + 192);
                 (*length_size) = 2;
         } else if (data[0] == 255) {
-                /* Five-byte length; we're not supposed to see this */
+                /* If support is added, adjust ECRYPTFS_MAX_PKT_LEN_SIZE */
                 ecryptfs_printk(KERN_ERR, "Five-byte packet length not "
                                 "supported\n");
                 rc = -EINVAL;
@@ -126,7 +126,7 @@ out:
 /**
  * ecryptfs_write_packet_length
  * @dest: The byte array target into which to write the length. Must
- *        have at least 5 bytes allocated.
+ *        have at least ECRYPTFS_MAX_PKT_LEN_SIZE 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.
@@ -146,6 +146,7 @@ int ecryptfs_write_packet_length(char *dest, size_t size,
                 dest[1] = ((size - 192) % 256);
                 (*packet_size_length) = 2;
         } else {
+                /* If support is added, adjust ECRYPTFS_MAX_PKT_LEN_SIZE */
                 rc = -EINVAL;
                 ecryptfs_printk(KERN_WARNING,
                                 "Unsupported packet size: [%zd]\n", size);
diff --git a/fs/ecryptfs/miscdev.c b/fs/ecryptfs/miscdev.c
index 1145c58103e2..349209dc6a91 100644
--- a/fs/ecryptfs/miscdev.c
+++ b/fs/ecryptfs/miscdev.c
@@ -218,6 +218,29 @@ out_unlock:
         return rc;
 }
 
+/*
+ * miscdevfs packet format:
+ *  Octet 0: Type
+ *  Octets 1-4: network byte order msg_ctx->counter
+ *  Octets 5-N0: Size of struct ecryptfs_message to follow
+ *  Octets N0-N1: struct ecryptfs_message (including data)
+ *
+ *  Octets 5-N1 not written if the packet type does not include a message
+ */
+#define PKT_TYPE_SIZE           1
+#define PKT_CTR_SIZE            4
+#define MIN_NON_MSG_PKT_SIZE    (PKT_TYPE_SIZE + PKT_CTR_SIZE)
+#define MIN_MSG_PKT_SIZE        (PKT_TYPE_SIZE + PKT_CTR_SIZE \
+                                 + ECRYPTFS_MIN_PKT_LEN_SIZE)
+/* 4 + ECRYPTFS_MAX_ENCRYPTED_KEY_BYTES comes from tag 65 packet format */
+#define MAX_MSG_PKT_SIZE        (PKT_TYPE_SIZE + PKT_CTR_SIZE \
+                                 + ECRYPTFS_MAX_PKT_LEN_SIZE \
+                                 + sizeof(struct ecryptfs_message) \
+                                 + 4 + ECRYPTFS_MAX_ENCRYPTED_KEY_BYTES)
+#define PKT_TYPE_OFFSET         0
+#define PKT_CTR_OFFSET          PKT_TYPE_SIZE
+#define PKT_LEN_OFFSET          (PKT_TYPE_SIZE + PKT_CTR_SIZE)
+
 /**
  * ecryptfs_miscdev_read - format and send message from queue
  * @file: fs/ecryptfs/euid miscdevfs handle (ignored)
@@ -237,7 +260,7 @@ ecryptfs_miscdev_read(struct file *file, char __user *buf, size_t count,
         struct ecryptfs_daemon *daemon;
         struct ecryptfs_msg_ctx *msg_ctx;
         size_t packet_length_size;
-        char packet_length[3];
+        char packet_length[ECRYPTFS_MAX_PKT_LEN_SIZE];
         size_t i;
         size_t total_length;
         uid_t euid = current_euid();
@@ -305,15 +328,8 @@ check_list:
                 packet_length_size = 0;
                 msg_ctx->msg_size = 0;
         }
-        /* miscdevfs packet format:
-         *  Octet 0: Type
-         *  Octets 1-4: network byte order msg_ctx->counter
-         *  Octets 5-N0: Size of struct ecryptfs_message to follow
-         *  Octets N0-N1: struct ecryptfs_message (including data)
-         *
-         *  Octets 5-N1 not written if the packet type does not
-         *  include a message */
-        total_length = (1 + 4 + packet_length_size + msg_ctx->msg_size);
+        total_length = (PKT_TYPE_SIZE + PKT_CTR_SIZE + packet_length_size
+                        + msg_ctx->msg_size);
         if (count < total_length) {
                 rc = 0;
                 printk(KERN_WARNING "%s: Only given user buffer of "
@@ -324,9 +340,10 @@ check_list:
         rc = -EFAULT;
         if (put_user(msg_ctx->type, buf))
                 goto out_unlock_msg_ctx;
-        if (put_user(cpu_to_be32(msg_ctx->counter), (__be32 __user *)(buf + 1)))
+        if (put_user(cpu_to_be32(msg_ctx->counter),
+                     (__be32 __user *)(&buf[PKT_CTR_OFFSET])))
                 goto out_unlock_msg_ctx;
-        i = 5;
+        i = PKT_TYPE_SIZE + PKT_CTR_SIZE;
         if (msg_ctx->msg) {
                 if (copy_to_user(&buf[i], packet_length, packet_length_size))
                         goto out_unlock_msg_ctx;
@@ -391,12 +408,6 @@ out:
  * @count: Amount of data in @buf
  * @ppos: Pointer to offset in file (ignored)
  *
- * miscdevfs packet format:
- *  Octet 0: Type
- *  Octets 1-4: network byte order msg_ctx->counter (0's for non-response)
- *  Octets 5-N0: Size of struct ecryptfs_message to follow
- *  Octets N0-N1: struct ecryptfs_message (including data)
- *
  * Returns the number of bytes read from @buf
  */
 static ssize_t
@@ -405,29 +416,25 @@ ecryptfs_miscdev_write(struct file *file, const char __user *buf,
 {
         __be32 counter_nbo;
         u32 seq;
-        size_t packet_size, packet_size_length, i;
+        size_t packet_size, packet_size_length;
         char *data;
         uid_t euid = current_euid();
-        unsigned char packet_size_peek[3];
+        unsigned char packet_size_peek[ECRYPTFS_MAX_PKT_LEN_SIZE];
         ssize_t rc;
 
         if (count == 0) {
                 return 0;
-        } else if (count == (1 + 4)) {
+        } else if (count == MIN_NON_MSG_PKT_SIZE) {
                 /* Likely a harmless MSG_HELO or MSG_QUIT - no packet length */
                 goto memdup;
-        } else if (count < (1 + 4 + 1)
-                   || count > (1 + 4 + 2 + sizeof(struct ecryptfs_message) + 4
-                               + ECRYPTFS_MAX_ENCRYPTED_KEY_BYTES)) {
+        } else if (count < MIN_MSG_PKT_SIZE || count > MAX_MSG_PKT_SIZE) {
                 printk(KERN_WARNING "%s: Acceptable packet size range is "
                        "[%d-%lu], but amount of data written is [%zu].",
-                       __func__, (1 + 4 + 1),
-                       (1 + 4 + 2 + sizeof(struct ecryptfs_message) + 4
-                        + ECRYPTFS_MAX_ENCRYPTED_KEY_BYTES), count);
+                       __func__, MIN_MSG_PKT_SIZE, MAX_MSG_PKT_SIZE, count);
                 return -EINVAL;
         }
 
-        if (copy_from_user(packet_size_peek, (buf + 1 + 4),
+        if (copy_from_user(packet_size_peek, &buf[PKT_LEN_OFFSET],
                            sizeof(packet_size_peek))) {
                 printk(KERN_WARNING "%s: Error while inspecting packet size\n",
                        __func__);
@@ -442,7 +449,8 @@ ecryptfs_miscdev_write(struct file *file, const char __user *buf,
                 return rc;
         }
 
-        if ((1 + 4 + packet_size_length + packet_size) != count) {
+        if ((PKT_TYPE_SIZE + PKT_CTR_SIZE + packet_size_length + packet_size)
+            != count) {
                 printk(KERN_WARNING "%s: Invalid packet size [%zu]\n", __func__,
                        packet_size);
                 return -EINVAL;
@@ -455,25 +463,25 @@ memdup:
                        __func__, PTR_ERR(data));
                 return PTR_ERR(data);
         }
-        i = 0;
-        switch (data[i++]) {
+        switch (data[PKT_TYPE_OFFSET]) {
         case ECRYPTFS_MSG_RESPONSE:
-                if (count < (1 + 4 + 1 + sizeof(struct ecryptfs_message))) {
+                if (count < (MIN_MSG_PKT_SIZE
+                             + sizeof(struct ecryptfs_message))) {
                         printk(KERN_WARNING "%s: Minimum acceptable packet "
                                "size is [%zd], but amount of data written is "
                                "only [%zd]. Discarding response packet.\n",
                                __func__,
-                               (1 + 4 + 1 + sizeof(struct ecryptfs_message)),
-                               count);
+                               (MIN_MSG_PKT_SIZE
+                                + sizeof(struct ecryptfs_message)), count);
                         rc = -EINVAL;
                         goto out_free;
                 }
-                memcpy(&counter_nbo, &data[i], 4);
+                memcpy(&counter_nbo, &data[PKT_CTR_OFFSET], PKT_CTR_SIZE);
                 seq = be32_to_cpu(counter_nbo);
-                i += 4 + packet_size_length;
-                rc = ecryptfs_miscdev_response(&data[i], packet_size,
-                                               euid, current_user_ns(),
-                                               task_pid(current), seq);
+                rc = ecryptfs_miscdev_response(
+                                &data[PKT_LEN_OFFSET + packet_size_length],
+                                packet_size, euid, current_user_ns(),
+                                task_pid(current), seq);
                 if (rc) {
                         printk(KERN_WARNING "%s: Failed to deliver miscdev "
                                "response to requesting operation; rc = [%zd]\n",