[FIXED] Possible deadlock

This is due to a re-entrant RLock(). It works sometimes, but if there
is a go routine requesting the write lock, then the second RLock()
will not be granted which will lead to a deadlock.
In summary: one should never make re-entrant RLock calls.

Signed-off-by: Ivan Kozlovic <ivan@synadia.com>

server/accounts.go

@@ -731,9 +731,16 @@ func (a *Account) hasMappings() bool {
 		return false
 	}
 	a.mu.RLock()
-	n := len(a.mappings)
+	hm := a.hasMappingsLocked()
 	a.mu.RUnlock()
-	return n > 0
+	return hm
+}
+
+// Indicates we have mapping entries.
+// The account has been verified to be non-nil.
+// Read or Write lock held on entry.
+func (a *Account) hasMappingsLocked() bool {
+	return len(a.mappings) > 0
 }
 
 // This performs the logic to map to a new dest subject based on mappings.

server/auth.go

@@ -706,7 +706,7 @@ func (s *Server) processClientOrLeafAuthentication(c *client, opts *Options) boo
 		acc.mu.RLock()
 		c.Debugf("Authenticated JWT: %s %q (claim-name: %q, claim-tags: %q) "+
 			"signed with %q by Account %q (claim-name: %q, claim-tags: %q) signed with %q has mappings %t accused %p",
-			c.kindString(), juc.Subject, juc.Name, juc.Tags, juc.Issuer, issuer, acc.nameTag, acc.tags, acc.Issuer, acc.hasMappings(), acc)
+			c.kindString(), juc.Subject, juc.Name, juc.Tags, juc.Issuer, issuer, acc.nameTag, acc.tags, acc.Issuer, acc.hasMappingsLocked(), acc)
 		acc.mu.RUnlock()
 		return true
 	}