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Improve resilience against memory attacks
To reduce residual fragments of secret data in memory after deallocation, this patch replaces the global delete operator with a version that zeros out previously allocated memory. It makes use of the new C++14 sized deallocation, but provides an unsized fallback with platform-specific size deductions. This change is only a minor mitigation and cannot protect against buffer reallocations by the operating system or non-C++ libraries. Thus, we still cannot guarantee all memory to be wiped after free. As a further improvement, this patch uses libgcrypt and libsodium to write long-lived master key component hashes into a secure memory area and wipe it afterwards. The patch also fixes compiler flags not being set properly on macOS.
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,89 @@ | ||
| /* | ||
| * Copyright (C) 2019 KeePassXC Team <[email protected]> | ||
| * | ||
| * This program is free software: you can redistribute it and/or modify | ||
| * it under the terms of the GNU General Public License as published by | ||
| * the Free Software Foundation, either version 2 or (at your option) | ||
| * version 3 of the License. | ||
| * | ||
| * This program is distributed in the hope that it will be useful, | ||
| * but WITHOUT ANY WARRANTY; without even the implied warranty of | ||
| * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | ||
| * GNU General Public License for more details. | ||
| * | ||
| * You should have received a copy of the GNU General Public License | ||
| * along with this program. If not, see <http://www.gnu.org/licenses/>. | ||
| */ | ||
|
|
||
| #include <QtGlobal> | ||
| #include <cstdint> | ||
| #include <sodium.h> | ||
| #ifdef Q_OS_MACOS | ||
| #include <malloc/malloc.h> | ||
| #else | ||
| #include <malloc.h> | ||
| #endif | ||
|
|
||
| #if defined(NDEBUG) && !defined(__cpp_sized_deallocation) | ||
| #warning "KeePassXC is being compiled without sized deallocation support. Deletes may be slow." | ||
| #endif | ||
|
|
||
| /** | ||
| * Custom sized delete operator which securely zeroes out allocated | ||
| * memory before freeing it (requires C++14 sized deallocation support). | ||
| */ | ||
| void operator delete(void* ptr, std::size_t size) noexcept | ||
| { | ||
| if (!ptr) { | ||
| return; | ||
| } | ||
|
|
||
| sodium_memzero(ptr, size); | ||
| std::free(ptr); | ||
| } | ||
|
|
||
| void operator delete[](void* ptr, std::size_t size) noexcept | ||
| { | ||
| ::operator delete(ptr, size); | ||
| } | ||
|
|
||
| /** | ||
| * Custom delete operator which securely zeroes out | ||
| * allocated memory before freeing it. | ||
| */ | ||
| void operator delete(void* ptr) noexcept | ||
| { | ||
| if (!ptr) { | ||
| return; | ||
| } | ||
|
|
||
| #if defined(Q_OS_WIN) | ||
| ::operator delete(ptr, _msize(ptr)); | ||
| #elif defined(Q_OS_MACOS) | ||
| ::operator delete(ptr, malloc_size(ptr)); | ||
| #elif defined(Q_OS_UNIX) | ||
| ::operator delete(ptr, malloc_usable_size(ptr)); | ||
| #else | ||
| // whatever OS this is, give up and simply free stuff | ||
| std::free(ptr); | ||
| #endif | ||
| } | ||
|
|
||
| void operator delete[](void* ptr) noexcept | ||
| { | ||
| ::operator delete(ptr); | ||
| } | ||
|
|
||
| /** | ||
| * Custom insecure delete operator that does not zero out memory before | ||
| * freeing a buffer. Can be used for better performance. | ||
| */ | ||
| void operator delete(void* ptr, bool) noexcept | ||
| { | ||
| std::free(ptr); | ||
| } | ||
|
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||
| void operator delete[](void* ptr, bool) noexcept | ||
| { | ||
| ::operator delete(ptr, false); | ||
| } |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -1,5 +1,5 @@ | ||
| /* | ||
| * Copyright (C) 2010 Felix Geyer <[email protected]> | ||
| * Copyright (C) 2019 KeePassXC Team <[email protected]> | ||
| * | ||
| * This program is free software: you can redistribute it and/or modify | ||
| * it under the terms of the GNU General Public License as published by | ||
|
|
@@ -16,35 +16,51 @@ | |
| */ | ||
|
|
||
| #include "PasswordKey.h" | ||
| #include "core/Tools.h" | ||
|
|
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| #include "crypto/CryptoHash.h" | ||
| #include <gcrypt.h> | ||
| #include <algorithm> | ||
| #include <cstring> | ||
|
|
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| QUuid PasswordKey::UUID("77e90411-303a-43f2-b773-853b05635ead"); | ||
|
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| constexpr int PasswordKey::SHA256_SIZE; | ||
|
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| PasswordKey::PasswordKey() | ||
| : Key(UUID) | ||
| , m_key(static_cast<char*>(gcry_malloc_secure(SHA256_SIZE))) | ||
| { | ||
| } | ||
|
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| PasswordKey::PasswordKey(const QString& password) | ||
| : Key(UUID) | ||
| , m_key(static_cast<char*>(gcry_malloc_secure(SHA256_SIZE))) | ||
| { | ||
| setPassword(password); | ||
| } | ||
|
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| PasswordKey::~PasswordKey() | ||
| { | ||
| if (m_key) { | ||
| gcry_free(m_key); | ||
| m_key = nullptr; | ||
| } | ||
| } | ||
|
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| QSharedPointer<PasswordKey> PasswordKey::fromRawKey(const QByteArray& rawKey) | ||
| { | ||
| auto result = QSharedPointer<PasswordKey>::create(); | ||
| result->m_key = rawKey; | ||
| std::memcpy(result->m_key, rawKey.data(), std::min(SHA256_SIZE, rawKey.size())); | ||
| return result; | ||
| } | ||
|
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| QByteArray PasswordKey::rawKey() const | ||
| { | ||
| return m_key; | ||
| return QByteArray::fromRawData(m_key, SHA256_SIZE); | ||
| } | ||
|
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| void PasswordKey::setPassword(const QString& password) | ||
| { | ||
| m_key = CryptoHash::hash(password.toUtf8(), CryptoHash::Sha256); | ||
| std::memcpy(m_key, CryptoHash::hash(password.toUtf8(), CryptoHash::Sha256).data(), SHA256_SIZE); | ||
| } | ||
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