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Andrew Chow 2c1fe27bf3
Merge bitcoin/bitcoin#27080: Wallet: Zero out wallet master key upon locking so it doesn't persist in memory 
3a11adc700 Zero out wallet master key upon lock (John Moffett)

Pull request description:

  When an encrypted wallet is locked (for instance via the RPC `walletlock`), the documentation indicates that the key is removed from memory:

  b92d609fb2/src/wallet/rpc/encrypt.cpp (L157-L158)

  However, the vector (a `std::vector<unsigned char, secure_allocator<unsigned char>>`) is merely _cleared_. As it is a member variable, it also stays in scope as long as the wallet is loaded, preventing the secure allocator from deallocating. This allows the key to persist indefinitely in memory. I confirmed this behavior on my macOS machine by using an open-source third party memory inspector ("Bit Slicer"). I was able to find my wallet's master key in Bit Slicer after unlocking and re-locking my encrypted wallet. I then confirmed the key data was at the address in LLDB.

  This PR manually fills the bytes with zeroes before calling `clear()` by using our `memory_cleanse` function, which is designed to prevent the compiler from optimizing it away. I confirmed that it does remove the data from memory on my machine upon locking.

  Note: An alternative approach could be to call `vMasterKey.shrink_to_fit()` after the `clear()`, which would trigger the secure allocator's deallocation. However, `shrink_to_fit()` is not _guaranteed_ to actually change the vector's capacity, so I think it's unwise to rely on it.

  ## Edit: A little more clarity on why this is an improvement.

  Since `mlock`ed memory is guaranteed not to be swapped to disk and our threat model doesn't consider a super-user monitoring the memory in realtime, why is this an improvement? Most importantly, consider hibernation. Even `mlock`ed memory may get written to disk. From the `mlock` [manpage](https://man7.org/linux/man-pages/man2/mlock.2.html):

  > (But be aware that the suspend mode on laptops and some desktop computers will save a copy of the system's RAM to disk, regardless of memory locks.)

  As far as I can tell, this is true of [Windows](https://web.archive.org/web/20190127110059/https://blogs.msdn.microsoft.com/oldnewthing/20140207-00/?p=1833#:~:text=%5BThere%20does%20not%20appear%20to%20be%20any%20guarantee%20that%20the%20memory%20won%27t%20be%20written%20to%20disk%20while%20locked.%20As%20you%20noted%2C%20the%20machine%20may%20be%20hibernated%2C%20or%20it%20may%20be%20running%20in%20a%20VM%20that%20gets%20snapshotted.%20%2DRaymond%5D) and macOS as well.

  Therefore, a user with a strong OS password and a strong wallet passphrase could still have their keys stolen if a thief takes their (hibernated) machine and reads the permanent storage.

ACKs for top commit:
  S3RK:
    Code review ACK 3a11adc700
  achow101:
    ACK 3a11adc700

Tree-SHA512: c4e3dab452ad051da74855a13aa711892c9b34c43cc43a45a3b1688ab044e75d715b42843c229219761913b4861abccbcc8d5cb6ac54957d74f6e357f04e8730
2023-02-13 15:18:16 -05:00
.github doc: remove usages of C++11 2023-01-12 13:42:44 +00:00
.tx Adjust .tx/config for new Transifex CLI 2022-10-15 19:11:39 +01:00
build-aux/m4 build: remove Boost lib detection from ax_boost_base 2023-01-13 10:41:33 +00:00
build_msvc Merge bitcoin/bitcoin#26691: Update secp256k1 subtree to libsecp256k1 version 0.2.0 2023-01-13 09:40:57 +00:00
ci Merge bitcoin/bitcoin#27033: ci: Cache stuff in volumes, not host folders 2023-02-13 11:53:50 +01:00
contrib Merge bitcoin/bitcoin#26701: contrib: make DNS seeds file an argument in CLI (makeseeds) 2023-02-07 10:03:36 +01:00
depends Merge bitcoin/bitcoin#26994: depends: define __BSD_VISIBLE for FreeBSD bdb build 2023-02-08 16:37:09 +01:00
doc Merge bitcoin/bitcoin#27016: mapport: require miniupnpc API version 17 or later 2023-02-13 16:25:09 +00:00
share build: add example bitcoin conf to win installer 2022-08-16 11:32:46 +01:00
src Merge bitcoin/bitcoin#27080: Wallet: Zero out wallet master key upon locking so it doesn't persist in memory 2023-02-13 15:18:16 -05:00
test Merge bitcoin/bitcoin#26970: test: fix immediate tx relay in wallet_groups.py 2023-02-13 11:51:03 +01:00
.cirrus.yml ci: Fix fingerprint_script for depends subdir caches 2023-02-09 22:20:42 +00:00
.editorconfig ci: Drop AppVeyor CI integration 2021-09-07 06:12:53 +03:00
.gitattributes Separate protocol versioning from clientversion 2014-10-29 00:24:40 -04:00
.gitignore refactor: cleanups post unsubtree'ing univalue 2022-06-15 12:56:44 +01:00
.python-version Bump minimum python version to 3.7 2023-01-18 12:59:11 +01:00
.style.yapf test: .style.yapf: Set column_limit=160 2019-03-04 18:28:13 -05:00
autogen.sh scripted-diff: Bump copyright of files changed in 2019 2019-12-30 10:42:20 +13:00
configure.ac Merge bitcoin/bitcoin#27016: mapport: require miniupnpc API version 17 or later 2023-02-13 16:25:09 +00:00
CONTRIBUTING.md doc: Explain squashing with merge commits 2022-05-24 08:17:41 +02:00
COPYING doc: Update license year range to 2023 2022-12-24 11:40:16 +01:00
INSTALL.md doc: Added hyperlink for doc/build 2021-09-09 19:53:12 +05:30
libbitcoinconsensus.pc.in build: remove libcrypto as internal dependency in libbitcoinconsensus.pc 2019-11-19 15:03:44 +01:00
Makefile.am build: package test_bitcoin in Windows installer 2022-08-09 09:13:23 +01:00
README.md doc: Explain Bitcoin Core in README.md 2022-05-10 07:49:09 +02:00
SECURITY.md doc: Add my key to SECURITY.md 2022-08-23 16:57:46 -04:00

README.md

Bitcoin Core integration/staging tree

https://bitcoincore.org

For an immediately usable, binary version of the Bitcoin Core software, see https://bitcoincore.org/en/download/.

What is Bitcoin Core?

Bitcoin Core connects to the Bitcoin peer-to-peer network to download and fully validate blocks and transactions. It also includes a wallet and graphical user interface, which can be optionally built.

Further information about Bitcoin Core is available in the doc folder.

License

Bitcoin Core is released under the terms of the MIT license. See COPYING for more information or see https://opensource.org/licenses/MIT.

Development Process

The master branch is regularly built (see doc/build-*.md for instructions) and tested, but it is not guaranteed to be completely stable. Tags are created regularly from release branches to indicate new official, stable release versions of Bitcoin Core.

The https://github.com/bitcoin-core/gui repository is used exclusively for the development of the GUI. Its master branch is identical in all monotree repositories. Release branches and tags do not exist, so please do not fork that repository unless it is for development reasons.

The contribution workflow is described in CONTRIBUTING.md and useful hints for developers can be found in doc/developer-notes.md.

Testing

Testing and code review is the bottleneck for development; we get more pull requests than we can review and test on short notice. Please be patient and help out by testing other people's pull requests, and remember this is a security-critical project where any mistake might cost people lots of money.

Automated Testing

Developers are strongly encouraged to write unit tests for new code, and to submit new unit tests for old code. Unit tests can be compiled and run (assuming they weren't disabled in configure) with: make check. Further details on running and extending unit tests can be found in /src/test/README.md.

There are also regression and integration tests, written in Python. These tests can be run (if the test dependencies are installed) with: test/functional/test_runner.py

The CI (Continuous Integration) systems make sure that every pull request is built for Windows, Linux, and macOS, and that unit/sanity tests are run automatically.

Manual Quality Assurance (QA) Testing

Changes should be tested by somebody other than the developer who wrote the code. This is especially important for large or high-risk changes. It is useful to add a test plan to the pull request description if testing the changes is not straightforward.

Translations

Changes to translations as well as new translations can be submitted to Bitcoin Core's Transifex page.

Translations are periodically pulled from Transifex and merged into the git repository. See the translation process for details on how this works.

Important: We do not accept translation changes as GitHub pull requests because the next pull from Transifex would automatically overwrite them again.