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crypto/decryptolm: retry prekey decryption with goolm

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This commit is contained in:
Tulir Asokan 2025-09-11 14:17:24 +03:00
commit 87fe127414
1 changed files with 27 additions and 1 deletions
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28
crypto/decryptolm.go
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@ -20,6 +20,7 @@ import (
"go.mau.fi/util/exerrors"
"go.mau.fi/util/ptr"
"maunium.net/go/mautrix/crypto/goolm/account"
"maunium.net/go/mautrix/event"
"maunium.net/go/mautrix/id"
)
@ -171,6 +172,7 @@ func (mach *OlmMachine) tryDecryptOlmCiphertext(ctx context.Context, sender id.U
return nil, DecryptionFailedForNormalMessage
}
accountBackup, err := mach.account.Internal.Pickle([]byte("tmp"))
log.Trace().Msg("Trying to create inbound session")
endTimeTrace = mach.timeTrace(ctx, "creating inbound olm session", time.Second)
session, err := mach.createInboundSession(ctx, senderKey, ciphertext)
@ -191,13 +193,20 @@ func (mach *OlmMachine) tryDecryptOlmCiphertext(ctx context.Context, sender id.U
plaintext, err = session.Decrypt(ciphertext, olmType)
endTimeTrace()
if err != nil {
go mach.unwedgeDevice(log, sender, senderKey)
log.Debug().
Hex("ciphertext_hash", ciphertextHash[:]).
Hex("ciphertext_hash_repeat", ptr.Ptr(exerrors.Must(olmMessageHash(ciphertext)))[:]).
Str("ciphertext", ciphertext).
Str("olm_session_description", session.Describe()).
Msg("DEBUG: Failed to decrypt prekey olm message with newly created session")
err2 := mach.goolmRetryHack(ctx, senderKey, ciphertext, accountBackup)
if err2 != nil {
log.Debug().Err(err2).Msg("Goolm confirmed decryption failure")
} else {
log.Warn().Msg("Goolm decryption was successful after libolm failure?")
}
go mach.unwedgeDevice(log, sender, senderKey)
return nil, fmt.Errorf("failed to decrypt olm event with session created from prekey message: %w", err)
}
@ -214,6 +223,23 @@ func (mach *OlmMachine) tryDecryptOlmCiphertext(ctx context.Context, sender id.U
return plaintext, nil
}
func (mach *OlmMachine) goolmRetryHack(ctx context.Context, senderKey id.SenderKey, ciphertext string, accountBackup []byte) error {
acc, err := account.AccountFromPickled(accountBackup, []byte("tmp"))
if err != nil {
return fmt.Errorf("failed to unpickle olm account: %w", err)
}
sess, err := acc.NewInboundSessionFrom(&senderKey, ciphertext)
if err != nil {
return fmt.Errorf("failed to create inbound session: %w", err)
}
_, err = sess.Decrypt(ciphertext, id.OlmMsgTypePreKey)
if err != nil {
// This is the expected result if libolm failed
return fmt.Errorf("failed to decrypt with new session: %w", err)
}
return nil
}
const MaxOlmSessionsPerDevice = 5
func (mach *OlmMachine) tryDecryptOlmCiphertextWithExistingSession(