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Parallelize volume header key derivation across layouts on mount #1793

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216 changes: 137 additions & 79 deletions src/Volume/Volume.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -14,6 +14,8 @@
#include <errno.h>
#endif
#include "EncryptionModeXTS.h"
#include "EncryptionThreadPool.h"
#include "Platform/Finally.h"
#include "Volume.h"
#include "VolumeHeader.h"
#include "VolumeLayout.h"
Expand Down Expand Up @@ -120,6 +122,114 @@ namespace VeraCrypt

bool skipLayoutV1Normal = false;

// Finalizes the volume once a layout's header has been decrypted.
// Shared by the serial and parallel header-detection paths below.
auto setupFromDecryptedHeader = [&](shared_ptr <VolumeLayout> layout, shared_ptr <VolumeHeader> header)

@idrassi idrassi Jul 8, 2026

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Please avoid lambdas here. This code is part of the common Unix/Linux volume path, and we still need to support CentOS 6 / GCC 4.4, where lambdas are not available. Please rewrite this helper using a GCC 4.4-compatible approach.

{
if (typeid (*layout) == typeid (VolumeLayoutV2Normal) && header->GetRequiredMinProgramVersion() < 0x10b)
{
// VolumeLayoutV1Normal has been opened as VolumeLayoutV2Normal
layout.reset (new VolumeLayoutV1Normal);
header->SetSize (layout->GetHeaderSize());
layout->SetHeader (header);
}

Pim = pim;
Type = layout->GetType();
SectorSize = header->GetSectorSize();

VolumeDataOffset = layout->GetDataOffset (VolumeHostSize);
VolumeDataSize = layout->GetDataSize (VolumeHostSize);
EncryptedDataSize = header->GetEncryptedAreaLength();

Header = header;
Layout = layout;
EA = header->GetEncryptionAlgorithm();
EncryptionMode &mode = *EA->GetMode();

if (layout->HasDriveHeader())
{
if (header->GetEncryptedAreaLength() != header->GetVolumeDataSize())
{
EncryptionNotCompleted = true;
// we avoid writing data to the partition since it is only partially encrypted
Protection = VolumeProtection::ReadOnly;
}

uint64 partitionStartOffset = VolumeFile->GetPartitionDeviceStartOffset();

if (partitionStartOffset < header->GetEncryptedAreaStart()
|| partitionStartOffset >= header->GetEncryptedAreaStart() + header->GetEncryptedAreaLength())
throw PasswordIncorrect (SRC_POS);

EncryptedDataSize -= partitionStartOffset - header->GetEncryptedAreaStart();

mode.SetSectorOffset (partitionStartOffset / ENCRYPTION_DATA_UNIT_SIZE);
}

// Volume protection
if (Protection == VolumeProtection::HiddenVolumeReadOnly)
{
if (Type == VolumeType::Hidden)
throw PasswordIncorrect (SRC_POS);
else
{
try
{
Volume protectedVolume;

protectedVolume.Open (VolumeFile,
protectionPassword, protectionPim, protectionKdf, protectionKeyfiles,
emvSupportEnabled,
VolumeProtection::ReadOnly,
shared_ptr <VolumePassword> (), 0, shared_ptr <Pkcs5Kdf> (),shared_ptr <KeyfileList> (),
VolumeType::Hidden,
useBackupHeaders);

if (protectedVolume.GetType() != VolumeType::Hidden)
ParameterIncorrect (SRC_POS);

ProtectedRangeStart = protectedVolume.VolumeDataOffset;
ProtectedRangeEnd = protectedVolume.VolumeDataOffset + protectedVolume.VolumeDataSize;
}
catch (PasswordException&)
{
if (protectionKeyfiles && !protectionKeyfiles->empty())
throw ProtectionPasswordKeyfilesIncorrect (SRC_POS);
throw ProtectionPasswordIncorrect (SRC_POS);
}
}
}
};

// When no specific KDF is requested and the encryption thread pool is
// available, gather every candidate layout header and derive their keys
// in parallel (VolumeHeader::DecryptHeaderParallel) so expensive KDFs
// (e.g. Argon2) for different layouts run concurrently instead of one
// layout at a time. Otherwise use the original serial detection.
// Start the encryption thread pool for parallel key derivation only if
// it is not already running (the GUI keeps a persistent pool). When we
// start it here -- e.g. in the elevated core service -- we also stop it
// before returning, so it is NOT running when the caller forks to launch
// the FUSE daemon (fork() in a multithreaded process is unsafe). The
// FUSE daemon starts its own pool after that fork.
bool encryptionPoolStartedHere = false;
if (!kdf && !EncryptionThreadPool::IsRunning())

@idrassi idrassi Jul 8, 2026

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Starting and stopping the global EncryptionThreadPool from Volume::Open is not safe as-is. The pool lifecycle is process-global, not reference-counted, and EncryptionThreadPool::Stop joins RunningThreads without clearing it. Repeated mount attempts, especially through the elevated service before the FUSE fork, can leave stale thread handles/global state. Please avoid changing the pool lifecycle from this path, or first make the pool lifecycle robust and serialized.

{
try
{
EncryptionThreadPool::Start();
encryptionPoolStartedHere = true;
}
catch (...) { }
}
finally_do_arg (bool, encryptionPoolStartedHere, { if (finally_arg) EncryptionThreadPool::Stop(); });

bool useParallelHeaderDetection = (!kdf && EncryptionThreadPool::IsRunning());
vector < shared_ptr <VolumeLayout> > candidateLayouts;
vector < shared_ptr <SecureBuffer> > candidateBuffers; // keep header buffers alive for the parallel call
vector <VolumeHeader::DecryptCandidate> candidates;

// Test volume layouts
foreach (shared_ptr <VolumeLayout> layout, VolumeLayout::GetAvailableLayouts (volumeType))
{
Expand All @@ -132,7 +242,7 @@ namespace VeraCrypt
if (useBackupHeaders && !layout->HasBackupHeader())
continue;

SecureBuffer headerBuffer (layout->GetHeaderSize());
shared_ptr <SecureBuffer> headerBuffer (new SecureBuffer (layout->GetHeaderSize()));

if (layout->HasDriveHeader())
{
Expand All @@ -152,7 +262,7 @@ namespace VeraCrypt
else
driveDevice.SeekEnd (headerOffset);

if (driveDevice.Read (headerBuffer) != layout->GetHeaderSize())
if (driveDevice.Read (*headerBuffer) != layout->GetHeaderSize())
continue;
}
else
Expand All @@ -167,7 +277,7 @@ namespace VeraCrypt
else
VolumeFile->SeekEnd (headerOffset);

if (VolumeFile->Read (headerBuffer) != layout->GetHeaderSize())
if (VolumeFile->Read (*headerBuffer) != layout->GetHeaderSize())
continue;
}

Expand All @@ -185,84 +295,32 @@ namespace VeraCrypt

shared_ptr <VolumeHeader> header = layout->GetHeader();

if (header->Decrypt (headerBuffer, *passwordKey, pim, kdf, layout->GetSupportedKeyDerivationFunctions(), layoutEncryptionAlgorithms, layoutEncryptionModes))
if (useParallelHeaderDetection)
{
// Header decrypted

if (typeid (*layout) == typeid (VolumeLayoutV2Normal) && header->GetRequiredMinProgramVersion() < 0x10b)
{
// VolumeLayoutV1Normal has been opened as VolumeLayoutV2Normal
layout.reset (new VolumeLayoutV1Normal);
header->SetSize (layout->GetHeaderSize());
layout->SetHeader (header);
}

Pim = pim;
Type = layout->GetType();
SectorSize = header->GetSectorSize();

VolumeDataOffset = layout->GetDataOffset (VolumeHostSize);
VolumeDataSize = layout->GetDataSize (VolumeHostSize);
EncryptedDataSize = header->GetEncryptedAreaLength();

Header = header;
Layout = layout;
EA = header->GetEncryptionAlgorithm();
EncryptionMode &mode = *EA->GetMode();

if (layout->HasDriveHeader())
{
if (header->GetEncryptedAreaLength() != header->GetVolumeDataSize())
{
EncryptionNotCompleted = true;
// we avoid writing data to the partition since it is only partially encrypted
Protection = VolumeProtection::ReadOnly;
}

uint64 partitionStartOffset = VolumeFile->GetPartitionDeviceStartOffset();

if (partitionStartOffset < header->GetEncryptedAreaStart()
|| partitionStartOffset >= header->GetEncryptedAreaStart() + header->GetEncryptedAreaLength())
throw PasswordIncorrect (SRC_POS);

EncryptedDataSize -= partitionStartOffset - header->GetEncryptedAreaStart();

mode.SetSectorOffset (partitionStartOffset / ENCRYPTION_DATA_UNIT_SIZE);
}
VolumeHeader::DecryptCandidate candidate;
candidate.Header = header;
candidate.EncryptedData = *headerBuffer;
candidate.KeyDerivationFunctions = layout->GetSupportedKeyDerivationFunctions();
candidate.EncryptionAlgorithms = layoutEncryptionAlgorithms;
candidate.EncryptionModes = layoutEncryptionModes;

candidates.push_back (candidate);
candidateLayouts.push_back (layout);
candidateBuffers.push_back (headerBuffer);
}
else if (header->Decrypt (*headerBuffer, *passwordKey, pim, kdf, layout->GetSupportedKeyDerivationFunctions(), layoutEncryptionAlgorithms, layoutEncryptionModes))
{
setupFromDecryptedHeader (layout, header);
return;
}
}

// Volume protection
if (Protection == VolumeProtection::HiddenVolumeReadOnly)
{
if (Type == VolumeType::Hidden)
throw PasswordIncorrect (SRC_POS);
else
{
try
{
Volume protectedVolume;

protectedVolume.Open (VolumeFile,
protectionPassword, protectionPim, protectionKdf, protectionKeyfiles,
emvSupportEnabled,
VolumeProtection::ReadOnly,
shared_ptr <VolumePassword> (), 0, shared_ptr <Pkcs5Kdf> (),shared_ptr <KeyfileList> (),
VolumeType::Hidden,
useBackupHeaders);

if (protectedVolume.GetType() != VolumeType::Hidden)
ParameterIncorrect (SRC_POS);

ProtectedRangeStart = protectedVolume.VolumeDataOffset;
ProtectedRangeEnd = protectedVolume.VolumeDataOffset + protectedVolume.VolumeDataSize;
}
catch (PasswordException&)
{
if (protectionKeyfiles && !protectionKeyfiles->empty())
throw ProtectionPasswordKeyfilesIncorrect (SRC_POS);
throw ProtectionPasswordIncorrect (SRC_POS);
}
}
}
if (useParallelHeaderDetection && !candidates.empty())
{
int winningCandidate = VolumeHeader::DecryptHeaderParallel (candidates, *passwordKey, pim);
if (winningCandidate >= 0)
{
setupFromDecryptedHeader (candidateLayouts[winningCandidate], candidates[winningCandidate].Header);
return;
}
}
Expand Down
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