Thomas Wolf created SSHD-860:
--------------------------------
Summary:
org.apache.sshd.client.auth.pubkey.UserAuthPublicKeyIterator pre-loads client
identities (private key files)
Key: SSHD-860
URL: https://issues.apache.org/jira/browse/SSHD-860
Project: MINA SSHD
Issue Type: Bug
Affects Versions: 2.0.0, 2.1.0, 2.1.1
Reporter: Thomas Wolf
{{org.apache.sshd.client.auth.pubkey.UserAuthPublicKeyIterator}} loads and
caches in memory private keys prematurely. Keys are loaded even if they are not
used at all in the end. In other words, incremental loading of keys doesn't
work.
This is bad for two reasons:
# Private keys should be kept in memory only if and when needed. Loading
completely unused private keys must be avoided.
# With encrypted private keys, the user may end up being asked for passphrases
for keys that are not used at all in the end, which is highly disruptive.
{{org.apache.sshd.client.auth.pubkey.UserAuthPublicKeyIterator}} does in its
constructor:
{code:java}
Iterator<? extends PublicKeyIdentity> current;
Collection<Stream<? extends PublicKeyIdentity>> identities = new LinkedList<>();
...
identities.add(Stream.of(ClientSession.providerOf(session))
.map(KeyIdentityProvider::loadKeys)
.flatMap(GenericUtils::stream)
.map(kp -> new KeyPairIdentity(signatureFactories, session, kp)));
current = identities.stream().flatMap(r -> r).iterator();
{code}
The final {{current}} iterator uses some internal buffer (size unknown; didn't
try to determine it) and will pre-fill this buffer completely. So with buffer
size _N_ it'll pre-load the first _N_ keys from the combined identity stream.
If the first key authenticates successfully, loading all the others must not be
done.
See my [test case|https://github.com/tomaswolf/mina-sshd/commit/a71c62e66]
showing this faulty behavior. It does exactly the same as the
{{UserAuthPublicKeyIterator}} constructor, using two iterators with two
identity files each, and then tests the resulting iterator. The first
{{hasNext()/next()}} call on the {{current}} iterator _loads all four keys!_
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