src/ssl/ssl_buffer.c

/* Copyright (c) 2015, Google Inc.
 *
 * Permission to use, copy, modify, and/or distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
 * SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
 * OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
 * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. */

#include <openssl/ssl.h>

#include <assert.h>
#include <limits.h>
#include <stdlib.h>
#include <string.h>

#include <openssl/bio.h>
#include <openssl/err.h>
#include <openssl/mem.h>
#include <openssl/type_check.h>

#include "internal.h"


OPENSSL_COMPILE_ASSERT(0xffff <= INT_MAX, uint16_fits_in_int);

OPENSSL_COMPILE_ASSERT((SSL3_ALIGN_PAYLOAD & (SSL3_ALIGN_PAYLOAD - 1)) == 0,
                       align_to_a_power_of_two);

/* setup_buffer initializes |buf| with capacity |cap|, aligned such that data
 * written after |header_len| is aligned to a |SSL3_ALIGN_PAYLOAD|-byte
 * boundary. It returns one on success and zero on error. */
static int setup_buffer(SSL3_BUFFER *buf, size_t header_len, size_t cap) {
  if (buf->buf != NULL || cap > 0xffff) {
    OPENSSL_PUT_ERROR(SSL, ERR_R_INTERNAL_ERROR);
    return 0;
  }

  /* Add up to |SSL3_ALIGN_PAYLOAD| - 1 bytes of slack for alignment. */
  buf->buf = OPENSSL_malloc(cap + SSL3_ALIGN_PAYLOAD - 1);
  if (buf->buf == NULL) {
    OPENSSL_PUT_ERROR(SSL, ERR_R_MALLOC_FAILURE);
    return 0;
  }

  /* Arrange the buffer such that the record body is aligned. */
  buf->offset = (0 - header_len - (uintptr_t)buf->buf) &
                (SSL3_ALIGN_PAYLOAD - 1);
  buf->len = 0;
  buf->cap = cap;
  return 1;
}

static void consume_buffer(SSL3_BUFFER *buf, size_t len) {
  if (len > buf->len) {
    abort();
  }
  buf->offset += (uint16_t)len;
  buf->len -= (uint16_t)len;
  buf->cap -= (uint16_t)len;
}

static void clear_buffer(SSL3_BUFFER *buf) {
  OPENSSL_free(buf->buf);
  memset(buf, 0, sizeof(SSL3_BUFFER));
}

OPENSSL_COMPILE_ASSERT(DTLS1_RT_HEADER_LENGTH + SSL3_RT_MAX_ENCRYPTED_LENGTH +
                           SSL3_RT_MAX_EXTRA <= 0xffff,
                       maximum_read_buffer_too_large);

/* setup_read_buffer initializes the read buffer if not already initialized. It
 * returns one on success and zero on failure. */
static int setup_read_buffer(SSL *ssl) {
  SSL3_BUFFER *buf = &ssl->s3->read_buffer;

  if (buf->buf != NULL) {
    return 1;
  }

  size_t header_len = ssl_record_prefix_len(ssl);
  size_t cap = SSL3_RT_MAX_ENCRYPTED_LENGTH;
  if (SSL_IS_DTLS(ssl)) {
    cap += DTLS1_RT_HEADER_LENGTH;
  } else {
    cap += SSL3_RT_HEADER_LENGTH;
  }
  if (ssl->options & SSL_OP_MICROSOFT_BIG_SSLV3_BUFFER) {
    cap += SSL3_RT_MAX_EXTRA;
  }

  return setup_buffer(buf, header_len, cap);
}

uint8_t *ssl_read_buffer(SSL *ssl) {
  return ssl->s3->read_buffer.buf + ssl->s3->read_buffer.offset;
}

size_t ssl_read_buffer_len(const SSL *ssl) {
  return ssl->s3->read_buffer.len;
}

static int dtls_read_buffer_next_packet(SSL *ssl) {
  SSL3_BUFFER *buf = &ssl->s3->read_buffer;

  if (buf->len > 0) {
    /* It is an error to call |dtls_read_buffer_extend| when the read buffer is
     * not empty. */
    OPENSSL_PUT_ERROR(SSL, ERR_R_INTERNAL_ERROR);
    return -1;
  }

  /* Read a single packet from |ssl->rbio|. |buf->cap| must fit in an int. */
  ssl->rwstate = SSL_READING;
  int ret = BIO_read(ssl->rbio, buf->buf + buf->offset, (int)buf->cap);
  if (ret <= 0) {
    return ret;
  }
  ssl->rwstate = SSL_NOTHING;
  /* |BIO_read| was bound by |buf->cap|, so this cannot overflow. */
  buf->len = (uint16_t)ret;
  return 1;
}

static int tls_read_buffer_extend_to(SSL *ssl, size_t len) {
  SSL3_BUFFER *buf = &ssl->s3->read_buffer;

  if (len > buf->cap) {
    /* This may occur if |SSL_OP_MICROSOFT_BIG_SSLV3_BUFFER| was toggled after
     * |setup_read_buffer| was called. Stay within bounds, but do not attempt to
     * recover. */
    OPENSSL_PUT_ERROR(SSL, SSL_R_BUFFER_TOO_SMALL);
    return -1;
  }

  /* Read until the target length is reached. */
  while (buf->len < len) {
    /* The amount of data to read is bounded by |buf->cap|, which must fit in an
     * int. */
    ssl->rwstate = SSL_READING;
    int ret = BIO_read(ssl->rbio, buf->buf + buf->offset + buf->len,
                       (int)(len - buf->len));
    if (ret <= 0) {
      return ret;
    }
    ssl->rwstate = SSL_NOTHING;
    /* |BIO_read| was bound by |buf->cap - buf->len|, so this cannot
     * overflow. */
    buf->len += (uint16_t)ret;
  }

  return 1;
}

int ssl_read_buffer_extend_to(SSL *ssl, size_t len) {
  /* |ssl_read_buffer_extend_to| implicitly discards any consumed data. */
  ssl_read_buffer_discard(ssl);

  if (!setup_read_buffer(ssl)) {
    return -1;
  }

  if (ssl->rbio == NULL) {
    OPENSSL_PUT_ERROR(SSL, SSL_R_BIO_NOT_SET);
    return -1;
  }

  ERR_clear_system_error();

  int ret;
  if (SSL_IS_DTLS(ssl)) {
    /* |len| is ignored for a datagram transport. */
    ret = dtls_read_buffer_next_packet(ssl);
  } else {
    ret = tls_read_buffer_extend_to(ssl, len);
  }

  if (ret <= 0) {
    /* If the buffer was empty originally and remained empty after attempting to
     * extend it, release the buffer until the next attempt. */
    ssl_read_buffer_discard(ssl);
  }
  return ret;
}

void ssl_read_buffer_consume(SSL *ssl, size_t len) {
  SSL3_BUFFER *buf = &ssl->s3->read_buffer;

  consume_buffer(buf, len);
  if (!SSL_IS_DTLS(ssl)) {
    /* The TLS stack never reads beyond the current record, so there will never
     * be unconsumed data. If read-ahead is ever reimplemented,
     * |ssl_read_buffer_discard| will require a |memcpy| to shift the excess
     * back to the front of the buffer, to ensure there is enough space for the
     * next record. */
     assert(buf->len == 0);
  }
}

void ssl_read_buffer_discard(SSL *ssl) {
  if (ssl->s3->read_buffer.len == 0) {
    ssl_read_buffer_clear(ssl);
  }
}

void ssl_read_buffer_clear(SSL *ssl) {
  clear_buffer(&ssl->s3->read_buffer);
}


int ssl_write_buffer_is_pending(const SSL *ssl) {
  return ssl->s3->write_buffer.len > 0;
}

OPENSSL_COMPILE_ASSERT(SSL3_RT_HEADER_LENGTH * 2 +
                           SSL3_RT_SEND_MAX_ENCRYPTED_OVERHEAD * 2 +
                           SSL3_RT_MAX_PLAIN_LENGTH <= 0xffff,
                       maximum_tls_write_buffer_too_large);

OPENSSL_COMPILE_ASSERT(DTLS1_RT_HEADER_LENGTH +
                           SSL3_RT_SEND_MAX_ENCRYPTED_OVERHEAD +
                           SSL3_RT_MAX_PLAIN_LENGTH <= 0xffff,
                       maximum_dtls_write_buffer_too_large);

int ssl_write_buffer_init(SSL *ssl, uint8_t **out_ptr, size_t max_len) {
  SSL3_BUFFER *buf = &ssl->s3->write_buffer;

  if (buf->buf != NULL) {
    OPENSSL_PUT_ERROR(SSL, ERR_R_INTERNAL_ERROR);
    return 0;
  }

  size_t header_len = ssl_seal_prefix_len(ssl);

  /* TODO(davidben): This matches the original behavior in keeping the malloc
   * size consistent. Does this matter? |cap| could just be |max_len|. */
  size_t cap = SSL3_RT_MAX_PLAIN_LENGTH + SSL3_RT_SEND_MAX_ENCRYPTED_OVERHEAD;
  if (SSL_IS_DTLS(ssl)) {
    cap += DTLS1_RT_HEADER_LENGTH;
  } else {
    cap += SSL3_RT_HEADER_LENGTH;
    if (ssl->mode & SSL_MODE_CBC_RECORD_SPLITTING) {
      cap += SSL3_RT_HEADER_LENGTH + SSL3_RT_SEND_MAX_ENCRYPTED_OVERHEAD;
    }
  }

  if (max_len > cap) {
    OPENSSL_PUT_ERROR(SSL, SSL_R_BUFFER_TOO_SMALL);
    return 0;
  }

  if (!setup_buffer(buf, header_len, cap)) {
    return 0;
  }
  *out_ptr = buf->buf + buf->offset;
  return 1;
}

void ssl_write_buffer_set_len(SSL *ssl, size_t len) {
  SSL3_BUFFER *buf = &ssl->s3->write_buffer;

  if (len > buf->cap) {
    abort();
  }
  buf->len = len;
}

static int tls_write_buffer_flush(SSL *ssl) {
  SSL3_BUFFER *buf = &ssl->s3->write_buffer;

  while (buf->len > 0) {
    ssl->rwstate = SSL_WRITING;
    int ret = BIO_write(ssl->wbio, buf->buf + buf->offset, buf->len);
    if (ret <= 0) {
      return ret;
    }
    ssl->rwstate = SSL_NOTHING;
    consume_buffer(buf, (size_t)ret);
  }
  ssl_write_buffer_clear(ssl);
  return 1;
}

static int dtls_write_buffer_flush(SSL *ssl) {
  SSL3_BUFFER *buf = &ssl->s3->write_buffer;
  if (buf->len == 0) {
    return 1;
  }

  ssl->rwstate = SSL_WRITING;
  int ret = BIO_write(ssl->wbio, buf->buf + buf->offset, buf->len);
  if (ret <= 0) {
    /* If the write failed, drop the write buffer anyway. Datagram transports
     * can't write half a packet, so the caller is expected to retry from the
     * top. */
    ssl_write_buffer_clear(ssl);
    return ret;
  }
  ssl->rwstate = SSL_NOTHING;
  ssl_write_buffer_clear(ssl);
  return 1;
}

int ssl_write_buffer_flush(SSL *ssl) {
  if (ssl->wbio == NULL) {
    OPENSSL_PUT_ERROR(SSL, SSL_R_BIO_NOT_SET);
    return -1;
  }
  ERR_clear_system_error();

  if (SSL_IS_DTLS(ssl)) {
    return dtls_write_buffer_flush(ssl);
  } else {
    return tls_write_buffer_flush(ssl);
  }
}

void ssl_write_buffer_clear(SSL *ssl) {
  clear_buffer(&ssl->s3->write_buffer);
}