[ 
https://issues.apache.org/jira/browse/SSHD-982?focusedWorklogId=425723&page=com.atlassian.jira.plugin.system.issuetabpanels:worklog-tabpanel#worklog-425723
 ]

ASF GitHub Bot logged work on SSHD-982:
---------------------------------------

                Author: ASF GitHub Bot
            Created on: 21/Apr/20 14:50
            Start Date: 21/Apr/20 14:50
    Worklog Time Spent: 10m 
      Work Description: lgoldstein commented on a change in pull request #124:
URL: https://github.com/apache/mina-sshd/pull/124#discussion_r412253325



##########
File path: 
sshd-core/src/main/java/org/apache/sshd/client/keyverifier/KnownHostsServerKeyVerifier.java
##########
@@ -153,35 +153,43 @@ public void 
setModifiedServerKeyAcceptor(ModifiedServerKeyAcceptor acceptor) {
 
     @Override
     public boolean verifyServerKey(ClientSession clientSession, SocketAddress 
remoteAddress, PublicKey serverKey) {
-        Collection<HostEntryPair> knownHosts = getLoadedHostsEntries();
         try {
             if (checkReloadRequired()) {
                 Path file = getPath();
                 if (exists()) {
-                    knownHosts = reloadKnownHosts(clientSession, file);
+                    updateReloadAttributes();
+                    keysSupplier = 
GenericUtils.memoizeLock(getKnownHostSupplier(clientSession, file));

Review comment:
       Update of keysSupplier field is not mutually exclusive...

##########
File path: 
sshd-core/src/main/java/org/apache/sshd/client/keyverifier/KnownHostsServerKeyVerifier.java
##########
@@ -153,35 +153,43 @@ public void 
setModifiedServerKeyAcceptor(ModifiedServerKeyAcceptor acceptor) {
 
     @Override
     public boolean verifyServerKey(ClientSession clientSession, SocketAddress 
remoteAddress, PublicKey serverKey) {
-        Collection<HostEntryPair> knownHosts = getLoadedHostsEntries();
         try {
             if (checkReloadRequired()) {
                 Path file = getPath();
                 if (exists()) {
-                    knownHosts = reloadKnownHosts(clientSession, file);
+                    updateReloadAttributes();
+                    keysSupplier = 
GenericUtils.memoizeLock(getKnownHostSupplier(clientSession, file));
                 } else {
                     if (log.isDebugEnabled()) {
                         log.debug("verifyServerKey({})[{}] missing known hosts 
file {}",
                                 clientSession, remoteAddress, file);
                     }
-                    knownHosts = Collections.emptyList();
+                    keysSupplier = 
GenericUtils.memoizeLock(Collections::emptyList);
                 }
-
-                setLoadedHostsEntries(knownHosts);
             }
         } catch (Throwable t) {
             return acceptIncompleteHostKeys(clientSession, remoteAddress, 
serverKey, t);
         }
 
+        Collection<HostEntryPair> knownHosts = keysSupplier.get();
+
         return acceptKnownHostEntries(clientSession, remoteAddress, serverKey, 
knownHosts);
     }
 
-    protected Collection<HostEntryPair> getLoadedHostsEntries() {
-        return keysHolder.get();
+    protected Supplier<Collection<HostEntryPair>> 
getKnownHostSupplier(ClientSession clientSession, Path file) {
+        return () -> {
+            try {
+                return reloadKnownHosts(clientSession, file);
+            } catch (Exception e) {
+                log.warn("verifyServerKey({}) Could not reload known hosts 
file {}",
+                        clientSession, file, e);
+                return Collections.emptyList();
+            }
+        };
     }
 
     protected void setLoadedHostsEntries(Collection<HostEntryPair> keys) {
-        keysHolder.set(keys);
+        keysSupplier = () -> keys;

Review comment:
       Update of keysSupplier field is not mutually exclusive...




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Issue Time Tracking
-------------------

    Worklog Id:     (was: 425723)
    Time Spent: 0.5h  (was: 20m)

> Race condition when loading known hosts
> ---------------------------------------
>
>                 Key: SSHD-982
>                 URL: https://issues.apache.org/jira/browse/SSHD-982
>             Project: MINA SSHD
>          Issue Type: Bug
>    Affects Versions: 2.4.0
>            Reporter: FliegenKLATSCH
>            Priority: Minor
>          Time Spent: 0.5h
>  Remaining Estimate: 0h
>
> When multiple (client) connections are instantiated in parallel the loaded 
> known hosts collection might be empty and therefore host key verification 
> fails.



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