view circbuffer.c @ 1861:2b3a8026a6ce

Add re-exec for server This allows ASLR to re-randomize the address space for every connection, preventing some vulnerabilities from being exploitable by repeated probing. Overhead (memory and time) is yet to be confirmed. At present this is only enabled on Linux. Other BSD platforms with fexecve() would probably also work though have not been tested.
author Matt Johnston <matt@ucc.asn.au>
date Sun, 30 Jan 2022 10:14:56 +0800
parents 06d52bcb8094
children
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/*
 * Dropbear SSH
 * 
 * Copyright (c) 2002-2004 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. */

#include "includes.h"
#include "dbutil.h"
#include "circbuffer.h"

#define MAX_CBUF_SIZE 100000000

circbuffer * cbuf_new(unsigned int size) {

	circbuffer *cbuf = NULL;

	if (size > MAX_CBUF_SIZE) {
		dropbear_exit("Bad cbuf size");
	}

	cbuf = (circbuffer*)m_malloc(sizeof(circbuffer));
	/* data is malloced on first write */
	cbuf->data = NULL;
	cbuf->used = 0;
	cbuf->readpos = 0;
	cbuf->writepos = 0;
	cbuf->size = size;

	return cbuf;
}

void cbuf_free(circbuffer * cbuf) {

	if (cbuf->data) {
		m_burn(cbuf->data, cbuf->size);
		m_free(cbuf->data);
	}
	m_free(cbuf);
}

unsigned int cbuf_getused(const circbuffer * cbuf) {

	return cbuf->used;

}

unsigned int cbuf_getavail(const circbuffer * cbuf) {

	return cbuf->size - cbuf->used;

}

unsigned int cbuf_writelen(const circbuffer *cbuf) {

	dropbear_assert(cbuf->used <= cbuf->size);
	dropbear_assert(((2*cbuf->size)+cbuf->writepos-cbuf->readpos)%cbuf->size == cbuf->used%cbuf->size);
	dropbear_assert(((2*cbuf->size)+cbuf->readpos-cbuf->writepos)%cbuf->size == (cbuf->size-cbuf->used)%cbuf->size);

	if (cbuf->used == cbuf->size) {
		TRACE(("cbuf_writelen: full buffer"))
		return 0; /* full */
	}
	
	if (cbuf->writepos < cbuf->readpos) {
		return cbuf->readpos - cbuf->writepos;
	}

	return cbuf->size - cbuf->writepos;
}

void cbuf_readptrs(const circbuffer *cbuf,
	unsigned char **p1, unsigned int *len1, 
	unsigned char **p2, unsigned int *len2) {
	*p1 = &cbuf->data[cbuf->readpos];
	*len1 = MIN(cbuf->used, cbuf->size - cbuf->readpos);

	if (*len1 < cbuf->used) {
		*p2 = cbuf->data;
		*len2 = cbuf->used - *len1;
	} else {
		*p2 = NULL;
		*len2 = 0;
	}
}

unsigned char* cbuf_writeptr(circbuffer *cbuf, unsigned int len) {

	if (len > cbuf_writelen(cbuf)) {
		dropbear_exit("Bad cbuf write");
	}

	if (!cbuf->data) {
		/* lazy allocation */
		cbuf->data = (unsigned char*)m_malloc(cbuf->size);
	}

	return &cbuf->data[cbuf->writepos];
}

void cbuf_incrwrite(circbuffer *cbuf, unsigned int len) {
	if (len > cbuf_writelen(cbuf)) {
		dropbear_exit("Bad cbuf write");
	}

	cbuf->used += len;
	dropbear_assert(cbuf->used <= cbuf->size);
	cbuf->writepos = (cbuf->writepos + len) % cbuf->size;
}


void cbuf_incrread(circbuffer *cbuf, unsigned int len) {
	dropbear_assert(cbuf->used >= len);
	cbuf->used -= len;
	cbuf->readpos = (cbuf->readpos + len) % cbuf->size;
}