Hi Dan - Thanks for taking a look at the code!
On 2014-10-21 15:04:35, Dan Carpenter wrote:
> fs/ecryptfs/keystore.c +93
> 85 /**
> 86 * ecryptfs_parse_packet_length
> 87 * @data: Pointer to memory containing length at offset
> 88 * @size: This function writes the decoded size to this memory
> 89 * address; zero on error
> 90 * @length_size: The number of bytes occupied by the encoded length
> 91 *
> 92 * Returns zero on success; non-zero on error
> 93 */
> 94 int ecryptfs_parse_packet_length(unsigned char *data, size_t *size,
> 95 size_t *length_size)
> 96 {
> 97 int rc = 0;
> 98
> 99 (*length_size) = 0;
> 100 (*size) = 0;
> 101 if (data[0] < 192) {
> 102 /* One-byte length */
> 103 (*size) = (unsigned char)data[0];
> 104 (*length_size) = 1;
> 105 } else if (data[0] < 224) {
> 106 /* Two-byte length */
> 107 (*size) = (((unsigned char)(data[0]) - 192) * 256);
> ^^^^^^^^^^^^^^^
> 108 (*size) += ((unsigned char)(data[1]) + 192);
> ^^^^^^^^^^^^^^^
> These casts are no-ops because they are "data" is an unsigned char
> pointer already. Then the value is type promoted to int, we subtract
> 192 giving a negative number and we multiply by 256 giving a slightly
> larger negative then we save it as a very large positive.
Subtracting 192 from data[0] should never result in a negative number.
We know that data[0] is greater than or equal to 192 (and less than 224)
because the previous conditional was false.
>
> I don't know this well enough to say what the intent was.
This method of specifying packet sizes came from RFC2440 "OpenPGP
Message Format" (https://tools.ietf.org/html/rfc2440#section-4.2.2).
Tyler
>
> 109 (*length_size) = 2;
> 110 } else if (data[0] == 255) {
> 111 /* If support is added, adjust ECRYPTFS_MAX_PKT_LEN_SIZE */
> 112 ecryptfs_printk(KERN_ERR, "Five-byte packet length not "
> 113 "supported\n");
> 114 rc = -EINVAL;
> 115 goto out;
> 116 } else {
> 117 ecryptfs_printk(KERN_ERR, "Error parsing packet length\n");
> 118 rc = -EINVAL;
> 119 goto out;
> 120 }
> 121 out:
> 122 return rc;
> 123 }
>
> regards,
> dan carpenter
> --
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