mirror of
http://galexander.org/git/simplesshd.git
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345 lines
8.4 KiB
C
345 lines
8.4 KiB
C
/*
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* Dropbear - a SSH2 server
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*
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* Copyright (c) 2002,2003 Matt Johnston
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* All rights reserved.
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*
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* Permission is hereby granted, free of charge, to any person obtaining a copy
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* of this software and associated documentation files (the "Software"), to deal
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* in the Software without restriction, including without limitation the rights
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* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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* copies of the Software, and to permit persons to whom the Software is
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* furnished to do so, subject to the following conditions:
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*
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* The above copyright notice and this permission notice shall be included in
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* all copies or substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
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* SOFTWARE. */
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#include "includes.h"
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#include "buffer.h"
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#include "dbutil.h"
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#include "bignum.h"
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#include "dbrandom.h"
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#include "runopts.h"
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/* this is used to generate unique output from the same hashpool */
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static uint32_t counter = 0;
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/* the max value for the counter, so it won't integer overflow */
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#define MAX_COUNTER (1<<30)
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static unsigned char hashpool[SHA1_HASH_SIZE] = {0};
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static int donerandinit = 0;
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#define INIT_SEED_SIZE 32 /* 256 bits */
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/* The basic setup is we read some data from /dev/(u)random or prngd and hash it
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* into hashpool. To read data, we hash together current hashpool contents,
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* and a counter. We feed more data in by hashing the current pool and new
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* data into the pool.
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*
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* It is important to ensure that counter doesn't wrap around before we
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* feed in new entropy.
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*
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*/
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/* Pass len=0 to hash an entire file */
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static int
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process_file(hash_state *hs, const char *filename,
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unsigned int len, int prngd)
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{
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static int already_blocked = 0;
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int readfd;
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unsigned int readcount;
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int ret = DROPBEAR_FAILURE;
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#if DROPBEAR_USE_PRNGD
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if (prngd)
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{
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readfd = connect_unix(filename);
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}
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else
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#endif
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{
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readfd = open(filename, O_RDONLY);
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}
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if (readfd < 0) {
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goto out;
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}
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readcount = 0;
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while (len == 0 || readcount < len)
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{
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int readlen, wantread;
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unsigned char readbuf[4096];
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if (!already_blocked && !prngd)
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{
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int res;
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struct timeval timeout;
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fd_set read_fds;
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timeout.tv_sec = 0;
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timeout.tv_usec = 1000;
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DROPBEAR_FD_ZERO(&read_fds);
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FD_SET(readfd, &read_fds);
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res = select(readfd + 1, &read_fds, NULL, NULL, &timeout);
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if (res == 0)
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{
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dropbear_log(LOG_WARNING, "Warning: Reading the randomness source '%s' seems to have blocked.\nYou may need to find a better entropy source.", filename);
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already_blocked = 1;
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}
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}
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if (already_blocked) break;
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if (len == 0)
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{
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wantread = sizeof(readbuf);
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}
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else
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{
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wantread = MIN(sizeof(readbuf), len-readcount);
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}
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#if DROPBEAR_USE_PRNGD
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if (prngd)
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{
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char egdcmd[2];
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egdcmd[0] = 0x02; /* blocking read */
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egdcmd[1] = (unsigned char)wantread;
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if (write(readfd, egdcmd, 2) < 0)
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{
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dropbear_exit("Can't send command to egd");
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}
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}
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#endif
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readlen = read(readfd, readbuf, wantread);
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if (readlen <= 0) {
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if (readlen < 0 && errno == EINTR) {
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continue;
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}
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if (readlen == 0 && len == 0)
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{
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/* whole file was read as requested */
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break;
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}
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goto out;
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}
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sha1_process(hs, readbuf, readlen);
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readcount += readlen;
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}
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ret = DROPBEAR_SUCCESS;
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out:
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close(readfd);
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return ret;
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}
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void addrandom(const unsigned char * buf, unsigned int len)
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{
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hash_state hs;
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#if DROPBEAR_FUZZ
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if (fuzz.fuzzing) {
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return;
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}
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#endif
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/* hash in the new seed data */
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sha1_init(&hs);
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/* existing state (zeroes on startup) */
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sha1_process(&hs, (void*)hashpool, sizeof(hashpool));
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/* new */
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sha1_process(&hs, buf, len);
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sha1_done(&hs, hashpool);
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}
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static void write_urandom()
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{
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#if DROPBEAR_FUZZ
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if (fuzz.fuzzing) {
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return;
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}
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#endif
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#if !DROPBEAR_USE_PRNGD
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/* This is opportunistic, don't worry about failure */
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unsigned char buf[INIT_SEED_SIZE];
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FILE *f = fopen(DROPBEAR_URANDOM_DEV, "w");
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if (!f) {
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return;
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}
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genrandom(buf, sizeof(buf));
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fwrite(buf, sizeof(buf), 1, f);
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fclose(f);
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#endif
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}
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#if DROPBEAR_FUZZ
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void fuzz_seed(void) {
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hash_state hs;
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sha1_init(&hs);
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sha1_process(&hs, "fuzzfuzzfuzz", strlen("fuzzfuzzfuzz"));
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sha1_done(&hs, hashpool);
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counter = 0;
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donerandinit = 1;
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}
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#endif
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/* Initialise the prng from /dev/urandom or prngd. This function can
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* be called multiple times */
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void seedrandom() {
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hash_state hs;
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pid_t pid;
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struct timeval tv;
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clock_t clockval;
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#if DROPBEAR_FUZZ
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if (fuzz.fuzzing) {
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return;
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}
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#endif
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/* hash in the new seed data */
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sha1_init(&hs);
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/* existing state */
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sha1_process(&hs, (void*)hashpool, sizeof(hashpool));
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#if DROPBEAR_USE_PRNGD
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if (process_file(&hs, DROPBEAR_PRNGD_SOCKET, INIT_SEED_SIZE, 1)
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!= DROPBEAR_SUCCESS) {
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dropbear_exit("Failure reading random device %s",
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DROPBEAR_PRNGD_SOCKET);
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}
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#else
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/* non-blocking random source (probably /dev/urandom) */
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if (process_file(&hs, DROPBEAR_URANDOM_DEV, INIT_SEED_SIZE, 0)
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!= DROPBEAR_SUCCESS) {
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dropbear_exit("Failure reading random device %s",
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DROPBEAR_URANDOM_DEV);
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}
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#endif
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/* A few other sources to fall back on.
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* Add more here for other platforms */
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#ifdef __linux__
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/* Seems to be a reasonable source of entropy from timers. Possibly hard
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* for even local attackers to reproduce */
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process_file(&hs, "/proc/timer_list", 4096, 0);
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/* Might help on systems with wireless */
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process_file(&hs, "/proc/interrupts", 4096, 0);
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process_file(&hs, "/proc/loadavg", 4096, 0);
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process_file(&hs, "/proc/sys/kernel/random/entropy_avail", 4096, 0);
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/* Mostly network visible but useful in some situations.
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* Limit size to avoid slowdowns on systems with lots of routes */
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process_file(&hs, "/proc/net/netstat", 4096, 0);
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process_file(&hs, "/proc/net/dev", 4096, 0);
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process_file(&hs, "/proc/net/tcp", 4096, 0);
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/* Also includes interface lo */
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process_file(&hs, "/proc/net/rt_cache", 4096, 0);
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process_file(&hs, "/proc/vmstat", 4096, 0);
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#endif
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pid = getpid();
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sha1_process(&hs, (void*)&pid, sizeof(pid));
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/* gettimeofday() doesn't completely fill out struct timeval on
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OS X (10.8.3), avoid valgrind warnings by clearing it first */
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memset(&tv, 0x0, sizeof(tv));
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gettimeofday(&tv, NULL);
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sha1_process(&hs, (void*)&tv, sizeof(tv));
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clockval = clock();
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sha1_process(&hs, (void*)&clockval, sizeof(clockval));
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/* When a private key is read by the client or server it will
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* be added to the hashpool - see runopts.c */
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sha1_done(&hs, hashpool);
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counter = 0;
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donerandinit = 1;
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/* Feed it all back into /dev/urandom - this might help if Dropbear
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* is running from inetd and gets new state each time */
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write_urandom();
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}
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/* return len bytes of pseudo-random data */
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void genrandom(unsigned char* buf, unsigned int len) {
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hash_state hs;
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unsigned char hash[SHA1_HASH_SIZE];
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unsigned int copylen;
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if (!donerandinit) {
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dropbear_exit("seedrandom not done");
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}
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while (len > 0) {
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sha1_init(&hs);
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sha1_process(&hs, (void*)hashpool, sizeof(hashpool));
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sha1_process(&hs, (void*)&counter, sizeof(counter));
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sha1_done(&hs, hash);
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counter++;
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if (counter > MAX_COUNTER) {
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seedrandom();
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}
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copylen = MIN(len, SHA1_HASH_SIZE);
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memcpy(buf, hash, copylen);
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len -= copylen;
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buf += copylen;
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}
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m_burn(hash, sizeof(hash));
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}
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/* Generates a random mp_int.
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* max is a *mp_int specifying an upper bound.
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* rand must be an initialised *mp_int for the result.
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* the result rand satisfies: 0 < rand < max
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* */
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void gen_random_mpint(mp_int *max, mp_int *rand) {
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unsigned char *randbuf = NULL;
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unsigned int len = 0;
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const unsigned char masks[] = {0xff, 0x01, 0x03, 0x07, 0x0f, 0x1f, 0x3f, 0x7f};
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const int size_bits = mp_count_bits(max);
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len = size_bits / 8;
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if ((size_bits % 8) != 0) {
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len += 1;
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}
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randbuf = (unsigned char*)m_malloc(len);
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do {
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genrandom(randbuf, len);
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/* Mask out the unrequired bits - mp_read_unsigned_bin expects
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* MSB first.*/
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randbuf[0] &= masks[size_bits % 8];
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bytes_to_mp(rand, randbuf, len);
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/* keep regenerating until we get one satisfying
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* 0 < rand < max */
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} while (!(mp_cmp(rand, max) == MP_LT && mp_cmp_d(rand, 0) == MP_GT));
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m_burn(randbuf, len);
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m_free(randbuf);
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}
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