From 0e6833b7707d677c9991e5b30dad4f0a68bab8dd Mon Sep 17 00:00:00 2001
From: Joakim Erdfelt <joakim.erdfelt@gmail.com>
Date: Tue, 12 Jul 2016 11:39:58 -0700
Subject: [PATCH] Issue #687 - Simplifying AllowSymLinkAliasChecker logic

---
 .../handler/AllowSymLinkAliasChecker.java     | 84 +++++++------------
 1 file changed, 30 insertions(+), 54 deletions(-)

diff --git a/jetty-server/src/main/java/org/eclipse/jetty/server/handler/AllowSymLinkAliasChecker.java b/jetty-server/src/main/java/org/eclipse/jetty/server/handler/AllowSymLinkAliasChecker.java
index 278a89831bc..a5d6bf016c6 100644
--- a/jetty-server/src/main/java/org/eclipse/jetty/server/handler/AllowSymLinkAliasChecker.java
+++ b/jetty-server/src/main/java/org/eclipse/jetty/server/handler/AllowSymLinkAliasChecker.java
@@ -29,9 +29,11 @@ import org.eclipse.jetty.util.resource.Resource;
 
 
 /* ------------------------------------------------------------ */
-/** Symbolic Link AliasChecker.
+
+/**
+ * Symbolic Link AliasChecker.
  * <p>An instance of this class can be registered with {@link ContextHandler#addAliasCheck(AliasCheck)}
- * to check resources that are aliased to other locations.   The checker uses the 
+ * to check resources that are aliased to other locations.   The checker uses the
  * Java {@link Files#readSymbolicLink(Path)} and {@link Path#toRealPath(java.nio.file.LinkOption...)}
  * APIs to check if a file is aliased with symbolic links.</p>
  */
@@ -46,7 +48,7 @@ public class AllowSymLinkAliasChecker implements AliasCheck
         if (!(resource instanceof PathResource))
             return false;
         
-        PathResource pathResource = (PathResource)resource;
+        PathResource pathResource = (PathResource) resource;
 
         try
         {
@@ -56,62 +58,14 @@ public class AllowSymLinkAliasChecker implements AliasCheck
             if (path.equals(alias))
                 return false; // Unknown why this is an alias
 
-            // is the file itself a symlink?
-            if (Files.isSymbolicLink(path))
-            {        
-                alias = path.getParent().resolve(alias);
-                if (LOG.isDebugEnabled())
-                {
-                    LOG.debug("path ={}",path);
-                    LOG.debug("alias={}",alias);
-                }
-                if (Files.isSameFile(path,alias))
-                {
-                    if (LOG.isDebugEnabled())
-                        LOG.debug("Allow symlink {} --> {}",resource,pathResource.getAliasPath());
-                    return true;
-                }
-            }
-
-            // No, so let's check each element ourselves
-            boolean linked=true;
-            Path target=path;
-            int loops=0;
-            while (linked)
-            {
-                if (++loops>100)
-                {
-                    if (LOG.isDebugEnabled())
-                        LOG.debug("Too many symlinks {} --> {}",resource,target);
-                    return false;
-                }
-                linked=false;
-                Path d = target.getRoot();
-                for (Path e:target)
-                {
-                    Path r=d.resolve(e);
-                    d=r;
-
-                    while (Files.exists(d) && Files.isSymbolicLink(d))
-                    {
-                        Path link=Files.readSymbolicLink(d);    
-                        if (!link.isAbsolute())
-                            link=d.getParent().resolve(link).normalize();
-                        d=link;
-                        linked=true;
-                    }
-                }
-                target=d;
-            }
-            
-            if (pathResource.getAliasPath().equals(target))
+            if (hasSymbolicLink(path) && Files.isSameFile(path, alias))
             {
                 if (LOG.isDebugEnabled())
-                    LOG.debug("Allow path symlink {} --> {}",resource,target);
+                    LOG.debug("Allow symlink {} --> {}", resource, pathResource.getAliasPath());
                 return true;
             }
         }
-        catch(Exception e)
+        catch (Exception e)
         {
             LOG.ignore(e);
         }
@@ -119,4 +73,26 @@ public class AllowSymLinkAliasChecker implements AliasCheck
         return false;
     }
 
+    private boolean hasSymbolicLink(Path path)
+    {
+        // Is file itself a symlink?
+        if (Files.isSymbolicLink(path))
+        {
+            return true;
+        }
+
+        // Lets try each path segment
+        Path base = path.getRoot();
+        for (Path segment : path)
+        {
+            base = base.resolve(segment);
+            if (Files.isSymbolicLink(base))
+            {
+                return true;
+            }
+        }
+
+        return false;
+    }
+
 }