mirror of https://github.com/c-ares/c-ares.git
* segment random number generation into own file * abstract random code to make it more modular so we can have multiple backends * rand: add support for arc4random_buf() and also direct CARES_RANDOM_FILE reading * autotools: fix detection of arc4random_buf * rework initial rc4 seed for PRNG as last fallback * rc4: more proper implementation, simplified for clarity * clarificationspull/522/head
Brad House
2 years ago
committed by
GitHub
parent
a2b8a4d434
commit
823df3b989
10 changed files with 387 additions and 126 deletions
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/* Copyright 1998 by the Massachusetts Institute of Technology.
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* Copyright (C) 2007-2013 by Daniel Stenberg |
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* |
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* Permission to use, copy, modify, and distribute this |
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* software and its documentation for any purpose and without |
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* fee is hereby granted, provided that the above copyright |
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* notice appear in all copies and that both that copyright |
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* notice and this permission notice appear in supporting |
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* documentation, and that the name of M.I.T. not be used in |
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* advertising or publicity pertaining to distribution of the |
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* software without specific, written prior permission. |
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* M.I.T. makes no representations about the suitability of |
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* this software for any purpose. It is provided "as is" |
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* without express or implied warranty. |
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*/ |
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#include "ares_setup.h" |
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#include "ares.h" |
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#include "ares_private.h" |
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#include "ares_nowarn.h" |
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#include <stdlib.h> |
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typedef enum { |
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ARES_RAND_OS = 1, /* OS-provided such as RtlGenRandom or arc4random */ |
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ARES_RAND_FILE = 2, /* OS file-backed random number generator */ |
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ARES_RAND_RC4 = 3 /* Internal RC4 based PRNG */ |
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} ares_rand_backend; |
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typedef struct ares_rand_rc4 |
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{ |
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unsigned char S[256]; |
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size_t i; |
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size_t j; |
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} ares_rand_rc4; |
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struct ares_rand_state |
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{ |
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ares_rand_backend type; |
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union { |
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FILE *rand_file; |
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ares_rand_rc4 rc4; |
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} state; |
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}; |
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/* Define RtlGenRandom = SystemFunction036. This is in advapi32.dll. There is
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* no need to dynamically load this, other software used widely does not. |
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* http://blogs.msdn.com/michael_howard/archive/2005/01/14/353379.aspx
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* https://docs.microsoft.com/en-us/windows/win32/api/ntsecapi/nf-ntsecapi-rtlgenrandom
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*/ |
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#ifdef _WIN32 |
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BOOLEAN WINAPI SystemFunction036(PVOID RandomBuffer, ULONG RandomBufferLength); |
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# ifndef RtlGenRandom |
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# define RtlGenRandom(a,b) SystemFunction036(a,b) |
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# endif |
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#endif |
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#define ARES_RC4_KEY_LEN 32 /* 256 bits */ |
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static unsigned int ares_u32_from_ptr(void *addr) |
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{ |
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if (sizeof(void *) == 8) { |
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return (unsigned int)((((size_t)addr >> 32) & 0xFFFFFFFF) | ((size_t)addr & 0xFFFFFFFF)); |
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} |
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return (unsigned int)((size_t)addr & 0xFFFFFFFF); |
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} |
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/* initialize an rc4 key as the last possible fallback. */ |
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static void ares_rc4_generate_key(ares_rand_rc4 *rc4_state, unsigned char *key, size_t key_len) |
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{ |
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size_t i; |
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size_t len = 0; |
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unsigned int data; |
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struct timeval tv; |
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if (key_len != ARES_RC4_KEY_LEN) |
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return; |
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/* Randomness is hard to come by. Maybe the system randomizes heap and stack addresses.
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* Maybe the current timestamp give us some randomness. |
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* Use rc4_state (heap), &i (stack), and ares__tvnow() |
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*/ |
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data = ares_u32_from_ptr(rc4_state); |
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memcpy(key + len, &data, sizeof(data)); |
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len += sizeof(data); |
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data = ares_u32_from_ptr(&i); |
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memcpy(key + len, &data, sizeof(data)); |
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len += sizeof(data); |
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tv = ares__tvnow(); |
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data = (unsigned int)((tv.tv_sec | tv.tv_usec) & 0xFFFFFFFF); |
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memcpy(key + len, &data, sizeof(data)); |
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len += sizeof(data); |
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srand(ares_u32_from_ptr(rc4_state) | ares_u32_from_ptr(&i) | (unsigned int)((tv.tv_sec | tv.tv_usec) & 0xFFFFFFFF)); |
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for (i=len; i<key_len; i++) { |
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key[i]=(unsigned char)(rand() % 256); /* LCOV_EXCL_LINE */ |
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} |
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} |
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static void ares_rc4_init(ares_rand_rc4 *rc4_state) |
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{ |
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unsigned char key[ARES_RC4_KEY_LEN]; |
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size_t i; |
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size_t j; |
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ares_rc4_generate_key(rc4_state, key, sizeof(key)); |
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for (i = 0; i < sizeof(rc4_state->S); i++) { |
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rc4_state->S[i] = i & 0xFF; |
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} |
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for(i = 0, j = 0; i < 256; i++) { |
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j = (j + rc4_state->S[i] + key[i % sizeof(key)]) % 256; |
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ARES_SWAP_BYTE(&rc4_state->S[i], &rc4_state->S[j]); |
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} |
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rc4_state->i = 0; |
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rc4_state->j = 0; |
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} |
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/* Just outputs the key schedule, no need to XOR with any data since we have none */ |
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static void ares_rc4_prng(ares_rand_rc4 *rc4_state, unsigned char *buf, int len) |
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{ |
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unsigned char *S = rc4_state->S; |
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size_t i = rc4_state->i; |
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size_t j = rc4_state->j; |
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size_t cnt; |
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for (cnt=0; cnt<len; cnt++) { |
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i = (i + 1) % 256; |
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j = (j + S[i]) % 256; |
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ARES_SWAP_BYTE(&S[i], &S[j]); |
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buf[cnt] = S[(S[i] + S[j]) % 256]; |
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} |
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rc4_state->i = i; |
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rc4_state->j = j; |
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} |
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static int ares__init_rand_engine(ares_rand_state *state) |
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{ |
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memset(state, 0, sizeof(*state)); |
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#if defined(HAVE_ARC4RANDOM_BUF) || defined(_WIN32) |
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state->type = ARES_RAND_OS; |
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return 1; |
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#elif defined(CARES_RANDOM_FILE) |
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state->type = ARES_RAND_FILE; |
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state->state.rand_file = fopen(CARES_RANDOM_FILE, "rb"); |
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if (state->state.rand_file) { |
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setvbuf(state->state.rand_file, NULL, _IONBF, 0); |
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return 1; |
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} |
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/* Fall-Thru on failure to RC4 */ |
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#endif |
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state->type = ARES_RAND_RC4; |
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ares_rc4_init(&state->state.rc4); |
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/* Currently cannot fail */ |
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return 1; |
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} |
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ares_rand_state *ares__init_rand_state() |
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{ |
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ares_rand_state *state = NULL; |
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state = ares_malloc(sizeof(*state)); |
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if (!state) |
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return NULL; |
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if (!ares__init_rand_engine(state)) { |
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ares_free(state); |
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return NULL; |
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} |
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return state; |
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} |
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static void ares__clear_rand_state(ares_rand_state *state) |
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{ |
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if (!state) |
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return; |
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switch (state->type) { |
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case ARES_RAND_OS: |
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break; |
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case ARES_RAND_FILE: |
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fclose(state->state.rand_file); |
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break; |
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case ARES_RAND_RC4: |
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break; |
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} |
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} |
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static void ares__reinit_rand(ares_rand_state *state) |
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{ |
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ares__clear_rand_state(state); |
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ares__init_rand_engine(state); |
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} |
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void ares__destroy_rand_state(ares_rand_state *state) |
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{ |
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if (!state) |
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return; |
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ares__clear_rand_state(state); |
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ares_free(state); |
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} |
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static void ares__rand_bytes(ares_rand_state *state, unsigned char *buf, size_t len) |
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{ |
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while (1) { |
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size_t rv; |
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size_t bytes_read = 0; |
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switch (state->type) { |
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case ARES_RAND_OS: |
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#ifdef _WIN32 |
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RtlGenRandom(buf, len); |
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return; |
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#elif defined(HAVE_ARC4RANDOM_BUF) |
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arc4random_buf(buf, len); |
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return; |
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#else |
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/* Shouldn't be possible to be here */ |
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break; |
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#endif |
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case ARES_RAND_FILE: |
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while (1) { |
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size_t rv = fread(buf + bytes_read, 1, len - bytes_read, state->state.rand_file); |
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if (rv == 0) |
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break; /* critical error, will reinit rand state */ |
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bytes_read += rv; |
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if (bytes_read == len) |
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return; |
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} |
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break; |
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case ARES_RAND_RC4: |
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ares_rc4_prng(&state->state.rc4, buf, len); |
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return; |
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} |
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/* If we didn't return before we got here, that means we had a critical rand
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* failure and need to reinitialized */ |
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ares__reinit_rand(state); |
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} |
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} |
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unsigned short ares__generate_new_id(ares_rand_state *state) |
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{ |
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unsigned short r=0; |
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ares__rand_bytes(state, (unsigned char *)&r, sizeof(r)); |
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return r; |
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} |
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