[PATCH 2.4] Fix d_path() truncating excessive long path name vulnerability

[Marc-Christian Petersen <m.c.p@wolk-project.de>]

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Hi Marcelo,

there isn't fixed the d_path() long name truncation vulnerability
(see http://cert.uni-stuttgart.de/archive/bugtraq/2002/03/msg00384.html) in
2.4.x up to 2.4.21-BK.

This trivial patch fixes it. Instead of truncating the path with no error, 
caller gets ENAMETOOLONG.

Patch credits go to Jirka Kosina.

Has been in WOLK and in -aa kernels for ages.

ciao, Marc

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--- linux/fs/dcache.c.orig	Mon Feb 25 20:38:08 2002
+++ linux/fs/dcache.c	Mon Apr  1 04:16:45 2002
@@ -976,14 +976,17 @@
 		parent = dentry->d_parent;
 		namelen = dentry->d_name.len;
 		buflen -= namelen + 1;
-		if (buflen < 0)
-			break;
+		if (buflen < 0){
+			retval = ERR_PTR(-ENAMETOOLONG);
+			goto out;
+		}
 		end -= namelen;
 		memcpy(end, dentry->d_name.name, namelen);
 		*--end = '/';
 		retval = end;
 		dentry = parent;
 	}
+out:
 	return retval;
 global_root:
 	namelen = dentry->d_name.len;
@@ -992,6 +995,8 @@
 		retval -= namelen-1;	/* hit the slash */
 		memcpy(retval, dentry->d_name.name, namelen);
 	}
+	else
+		retval = ERR_PTR(-ENAMETOOLONG);
 	return retval;
 }
 
@@ -1041,8 +1046,11 @@
 		spin_unlock(&dcache_lock);
 
 		error = -ERANGE;
+		
+		if (cwd == ERR_PTR(-ENAMETOOLONG)) error = -ENAMETOOLONG;
+
 		len = PAGE_SIZE + page - cwd;
-		if (len <= size) {
+		if (len <= size && error != -ENAMETOOLONG) {
 			error = len;
 			if (copy_to_user(buf, cwd, len))
 				error = -EFAULT;