/*

 * Dropbear SSH

 * 

 * Copyright (c) 2002,2003 Matt Johnston

 * All rights reserved.

 * 

 * Permission is hereby granted, free of charge, to any person obtaining a copy

 * of this software and associated documentation files (the "Software"), to deal

 * in the Software without restriction, including without limitation the rights

 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell

 * copies of the Software, and to permit persons to whom the Software is

 * furnished to do so, subject to the following conditions:

 * 

 * The above copyright notice and this permission notice shall be included in

 * all copies or substantial portions of the Software.

 * 

 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR

 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,

 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE

 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER

 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,

 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE

 * SOFTWARE. */

/* Buffer handling routines, designed to avoid overflows/using invalid data */

#include "includes.h"

#include "dbutil.h"

#include "buffer.h"

/* Prevent integer overflows when incrementing buffer position/length.

 * Calling functions should check arguments first, but this provides a

 * backstop */

#define BUF_MAX_INCR 1000000000

#define BUF_MAX_SIZE 1000000000

/* avoid excessively large numbers, > ~8192 bits */

#define BUF_MAX_MPINT (8240 / 8)

/* Create (malloc) a new buffer of size */

buffer* buf_new(unsigned int size) {

  buffer* buf;

  if (size > BUF_MAX_SIZE) {

    dropbear_exit("buf->size too big");

  }

  buf = (buffer*)m_malloc(sizeof(buffer)+size);

  buf->data = (unsigned char*)buf + sizeof(buffer);

  buf->size = size;

  return buf;

}

/* free the buffer's data and the buffer itself */

void buf_free(buffer* buf) {

  m_free(buf);

}

/* overwrite the contents of the buffer then free it */

void buf_burn_free(buffer* buf) {

  m_burn(buf->data, buf->size);

  m_free(buf);

}

/* resize a buffer, pos and len will be repositioned if required when

 * downsizing */

buffer* buf_resize(buffer *buf, unsigned int newsize) {

  if (newsize > BUF_MAX_SIZE) {

    dropbear_exit("buf->size too big");

  }

  buf = m_realloc(buf, sizeof(buffer)+newsize);

  buf->data = (unsigned char*)buf + sizeof(buffer);

  buf->size = newsize;

  buf->len = MIN(newsize, buf->len);

  buf->pos = MIN(newsize, buf->pos);

  return buf;

}

/* Create a copy of buf, allocating required memory etc. */

/* The new buffer is sized the same as the length of the source buffer. */

buffer* buf_newcopy(const buffer* buf) {

  buffer* ret;

  ret = buf_new(buf->len);

  ret->len = buf->len;

  if (buf->len > 0) {

    memcpy(ret->data, buf->data, buf->len);

  }

  return ret;

}

/* Set the length of the buffer */

void buf_setlen(buffer* buf, unsigned int len) {

  if (len > buf->size) {

    dropbear_exit("Bad buf_setlen");

  }

  buf->len = len;

  buf->pos = MIN(buf->pos, buf->len);

}

/* Increment the length of the buffer */

void buf_incrlen(buffer* buf, unsigned int incr) {

  if (incr > BUF_MAX_INCR || buf->len + incr > buf->size) {

    dropbear_exit("Bad buf_incrlen");

  }

  buf->len += incr;

}

/* Set the position of the buffer */

void buf_setpos(buffer* buf, unsigned int pos) {

  if (pos > buf->len) {

    dropbear_exit("Bad buf_setpos");

  }

  buf->pos = pos;

}

/* increment the position by incr, increasing the buffer length if required */

void buf_incrwritepos(buffer* buf, unsigned int incr) {

  if (incr > BUF_MAX_INCR || buf->pos + incr > buf->size) {

    dropbear_exit("Bad buf_incrwritepos");

  }

  buf->pos += incr;

  if (buf->pos > buf->len) {

    buf->len = buf->pos;

  }

}

/* increment the position by incr */

void buf_incrpos(buffer* buf, unsigned int incr) {

  if (incr > BUF_MAX_INCR 

    || (buf->pos + incr) > buf->len) {

    dropbear_exit("Bad buf_incrpos");

  }

  buf->pos += incr;

}

/* decrement the position by decr */

void buf_decrpos(buffer* buf, unsigned int decr) {

  if (decr > buf->pos) {

    dropbear_exit("Bad buf_decrpos");

  }

  buf->pos -= decr;

}

/* Get a byte from the buffer and increment the pos */

unsigned char buf_getbyte(buffer* buf) {

  /* This check is really just ==, but the >= allows us to check for the

   * bad case of pos > len, which should _never_ happen. */

  if (buf->pos >= buf->len) {

    dropbear_exit("Bad buf_getbyte");

  }

  return buf->data[buf->pos++];

}

/* Get a bool from the buffer and increment the pos */

unsigned char buf_getbool(buffer* buf) {

  unsigned char b;

  b = buf_getbyte(buf);

  if (b != 0)

    b = 1;

  return b;

}

/* put a byte, incrementing the length if required */

void buf_putbyte(buffer* buf, unsigned char val) {

  if (buf->pos >= buf->len) {

    buf_incrlen(buf, 1);

  }

  buf->data[buf->pos] = val;

  buf->pos++;

}

/* returns an in-place pointer to the buffer, checking that

 * the next len bytes from that position can be used */

unsigned char* buf_getptr(const buffer* buf, unsigned int len) {

  if (len > BUF_MAX_INCR || buf->pos + len > buf->len) {

    dropbear_exit("Bad buf_getptr");

  }

  return &buf->data[buf->pos];

}

/* like buf_getptr, but checks against total size, not used length.

 * This allows writing past the used length, but not past the size */

unsigned char* buf_getwriteptr(const buffer* buf, unsigned int len) {

  if (len > BUF_MAX_INCR || buf->pos + len > buf->size) {

    dropbear_exit("Bad buf_getwriteptr");

  }

  return &buf->data[buf->pos];

}

/* Return a null-terminated string, it is malloced, so must be free()ed

 * Note that the string isn't checked for null bytes, hence the retlen

 * may be longer than what is returned by strlen */

char* buf_getstring(buffer* buf, unsigned int *retlen) {

  unsigned int len;

  char* ret;

  void* src = NULL;

  len = buf_getint(buf);

  if (len > MAX_STRING_LEN) {

    dropbear_exit("String too long");

  }

  if (retlen != NULL) {

    *retlen = len;

  }

  src = buf_getptr(buf, len);

  ret = m_malloc(len+1);

  memcpy(ret, src, len);

  buf_incrpos(buf, len);

  ret[len] = '\0';

  return ret;

}

/* Return a string as a newly allocated buffer */

static buffer * buf_getstringbuf_int(buffer *buf, int incllen) {

  buffer *ret = NULL;

  unsigned int len = buf_getint(buf);

  int extra = 0;

  if (len > MAX_STRING_LEN) {

    dropbear_exit("String too long");

  }

  if (incllen) {

    extra = 4;

  }

  ret = buf_new(len+extra);

  if (incllen) {

    buf_putint(ret, len);

  }

  memcpy(buf_getwriteptr(ret, len), buf_getptr(buf, len), len);

  buf_incrpos(buf, len);

  buf_incrlen(ret, len);

  buf_setpos(ret, 0);

  return ret;

}

/* Return a string as a newly allocated buffer */

buffer * buf_getstringbuf(buffer *buf) {

  return buf_getstringbuf_int(buf, 0);

}

/* Returns a string in a new buffer, including the length */

buffer * buf_getbuf(buffer *buf) {

  return buf_getstringbuf_int(buf, 1);

}

/* Returns the equivalent of buf_getptr() as a new buffer. */

buffer * buf_getptrcopy(const buffer* buf, unsigned int len) {

  unsigned char *src = buf_getptr(buf, len);

  buffer *ret = buf_new(len);

  buf_putbytes(ret, src, len);

  buf_setpos(ret, 0);

  return ret;

}

/* Just increment the buffer position the same as if we'd used buf_getstring,

 * but don't bother copying/malloc()ing for it */

void buf_eatstring(buffer *buf) {

  buf_incrpos( buf, buf_getint(buf) );

}

/* Get an uint32 from the buffer and increment the pos */

unsigned int buf_getint(buffer* buf) {

  unsigned int ret;

  LOAD32H(ret, buf_getptr(buf, 4));

  buf_incrpos(buf, 4);

  return ret;

}

/* put a 32bit uint into the buffer, incr bufferlen & pos if required */

void buf_putint(buffer* buf, int unsigned val) {

  STORE32H(val, buf_getwriteptr(buf, 4));

  buf_incrwritepos(buf, 4);

}

/* put a SSH style string into the buffer, increasing buffer len if required */

void buf_putstring(buffer* buf, const char* str, unsigned int len) {

  buf_putint(buf, len);

  buf_putbytes(buf, (const unsigned char*)str, len);

}

/* puts an entire buffer as a SSH string. ignore pos of buf_str. */

void buf_putbufstring(buffer *buf, const buffer* buf_str) {

  buf_putstring(buf, (const char*)buf_str->data, buf_str->len);

}

/* put the set of len bytes into the buffer, incrementing the pos, increasing

 * len if required */

void buf_putbytes(buffer *buf, const unsigned char *bytes, unsigned int len) {

  memcpy(buf_getwriteptr(buf, len), bytes, len);

  buf_incrwritepos(buf, len);

}

/* for our purposes we only need positive (or 0) numbers, so will

 * fail if we get negative numbers */

void buf_putmpint(buffer* buf, const mp_int * mp) {

  size_t written;

  unsigned int len, pad = 0;

  TRACE2(("enter buf_putmpint"))

  dropbear_assert(mp != NULL);

  if (mp_isneg(mp)) {

    dropbear_exit("negative bignum");

  }

  /* zero check */

  if (mp_iszero(mp)) {

    len = 0;

  } else {

    /* SSH spec requires padding for mpints with the MSB set, this code

     * implements it */

    len = mp_count_bits(mp);

    /* if the top bit of MSB is set, we need to pad */

    pad = (len%8 == 0) ? 1 : 0;

    len = len / 8 + 1; /* don't worry about rounding, we need it for

                padding anyway when len%8 == 0 */

  }

  /* store the length */

  buf_putint(buf, len);

  /* store the actual value */

  if (len > 0) {

    if (pad) {

      buf_putbyte(buf, 0x00);

    }

    if (mp_to_ubin(mp, buf_getwriteptr(buf, len-pad), len-pad, &written) != MP_OKAY) {

      dropbear_exit("mpint error");

    }

    buf_incrwritepos(buf, written);

  }

  TRACE2(("leave buf_putmpint"))

}

/* Retrieve an mp_int from the buffer.

 * Will fail for -ve since they shouldn't be required here.

 * Returns DROPBEAR_SUCCESS or DROPBEAR_FAILURE */

int buf_getmpint(buffer* buf, mp_int* mp) {

  unsigned int len;

  len = buf_getint(buf);

  if (len == 0) {

    mp_zero(mp);

    return DROPBEAR_SUCCESS;

  }

  if (len > BUF_MAX_MPINT) {

    return DROPBEAR_FAILURE;

  }

  /* check for negative */

  if (*buf_getptr(buf, 1) & (1 << (CHAR_BIT-1))) {

    return DROPBEAR_FAILURE;

  }

  if (mp_from_ubin(mp, buf_getptr(buf, len), len) != MP_OKAY) {

    return DROPBEAR_FAILURE;

  }

  buf_incrpos(buf, len);

  return DROPBEAR_SUCCESS;

}