forked from mirrors/gecko-dev
bc96439261
Using a weak RNG for the form boundary allows a website operator to perform several attacks on users (as outlined in https://trac.torproject.org/projects/tor/ticket/22919) These include: - Identifying Windows users based on the unseeded RNG - Identify the number of form submissions that have occurred cross-origin between same-origin submissions Additionally, a predictable boundary makes it possible to forge a boundary in the middle of a file upload. Differential Revision: https://phabricator.services.mozilla.com/D56056 --HG-- extra : moz-landing-system : lando
161 lines
4.2 KiB
C++
161 lines
4.2 KiB
C++
/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
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/* vim: set ts=8 sts=2 et sw=2 tw=80: */
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/* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at https://mozilla.org/MPL/2.0/. */
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#include "mozilla/RandomNum.h"
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#include <fcntl.h>
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#ifdef XP_UNIX
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# include <unistd.h>
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#endif
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#if defined(XP_WIN)
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// Microsoft doesn't "officially" support using RtlGenRandom() directly
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// anymore, and the Windows headers assume that __stdcall is
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// the default calling convention (which is true when Microsoft uses this
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// function to build their own CRT libraries).
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// We will explicitly declare it with the proper calling convention.
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# include "minwindef.h"
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# define RtlGenRandom SystemFunction036
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extern "C" BOOLEAN NTAPI RtlGenRandom(PVOID RandomBuffer,
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ULONG RandomBufferLength);
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#endif
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#if defined(ANDROID) || defined(XP_DARWIN) || defined(__DragonFly__) || \
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defined(__FreeBSD__) || defined(__NetBSD__) || defined(__OpenBSD__)
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# include <stdlib.h>
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# define USE_ARC4RANDOM
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#endif
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#if defined(__linux__)
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# include <linux/random.h> // For GRND_NONBLOCK.
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# include <sys/syscall.h> // For SYS_getrandom.
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// Older glibc versions don't define SYS_getrandom, so we define it here if
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// it's not available. See bug 995069.
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# if defined(__x86_64__)
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# define GETRANDOM_NR 318
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# elif defined(__i386__)
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# define GETRANDOM_NR 355
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# elif defined(__aarch64__)
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# define GETRANDOM_NR 278
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# elif defined(__arm__)
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# define GETRANDOM_NR 384
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# elif defined(__powerpc__)
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# define GETRANDOM_NR 359
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# elif defined(__s390__)
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# define GETRANDOM_NR 349
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# elif defined(__mips__)
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# include <sgidefs.h>
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# if _MIPS_SIM == _MIPS_SIM_ABI32
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# define GETRANDOM_NR 4353
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# elif _MIPS_SIM == _MIPS_SIM_ABI64
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# define GETRANDOM_NR 5313
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# elif _MIPS_SIM == _MIPS_SIM_NABI32
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# define GETRANDOM_NR 6317
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# endif
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# endif
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# if defined(SYS_getrandom)
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// We have SYS_getrandom. Use it to check GETRANDOM_NR. Only do this if we set
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// GETRANDOM_NR so tier 3 platforms with recent glibc are not forced to define
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// it for no good reason.
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# if defined(GETRANDOM_NR)
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static_assert(GETRANDOM_NR == SYS_getrandom,
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"GETRANDOM_NR should match the actual SYS_getrandom value");
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# endif
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# else
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# define SYS_getrandom GETRANDOM_NR
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# endif
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# if defined(GRND_NONBLOCK)
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static_assert(GRND_NONBLOCK == 1,
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"If GRND_NONBLOCK is not 1 the #define below is wrong");
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# else
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# define GRND_NONBLOCK 1
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# endif
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#endif // defined(__linux__)
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namespace mozilla {
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/*
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* Note - Bug 1500115 has been opened to discuss simplifying or improving
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* this function in the future; however, the function is secure as-is right
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* now. Further improvements may be made to reduce complexity, improve
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* robustness, or take advantage of OS-specific API improvements as they
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* become available.
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*
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*/
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MFBT_API Maybe<uint64_t> RandomUint64() {
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#if defined(XP_WIN)
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uint64_t result = 0;
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if (!RtlGenRandom(&result, sizeof(result))) {
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return Nothing();
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}
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return Some(result);
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#elif defined(USE_ARC4RANDOM) // defined(XP_WIN)
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return Some((static_cast<uint64_t>(arc4random()) << 32) | arc4random());
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#elif defined(XP_UNIX) // defined(USE_ARC4RANDOM)
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uint64_t result = 0;
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# if defined(__linux__)
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long bytesGenerated =
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syscall(SYS_getrandom, &result, sizeof(result), GRND_NONBLOCK);
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if ((bytesGenerated > 0) &&
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(static_cast<unsigned long>(bytesGenerated) == sizeof(result))) {
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return Some(result);
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}
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// Fall-through to UNIX behavior if failed
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# endif // defined(__linux__)
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int fd = open("/dev/urandom", O_RDONLY);
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if (fd < 0) {
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return Nothing();
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}
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ssize_t bytesRead = read(fd, &result, sizeof(result));
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close(fd);
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if (bytesRead < 0) {
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return Nothing();
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}
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if (static_cast<size_t>(bytesRead) != sizeof(result)) {
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return Nothing();
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}
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return Some(result);
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#else // defined(XP_UNIX)
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# error "Platform needs to implement RandomUint64()"
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#endif
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}
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MFBT_API uint64_t RandomUint64OrDie() {
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Maybe<uint64_t> maybeRandomNum = RandomUint64();
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MOZ_RELEASE_ASSERT(maybeRandomNum.isSome());
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return maybeRandomNum.value();
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}
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} // namespace mozilla
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