Re: [PATCH] nfs client, kernel 2.4.31: readlink result overflow

[Assar <assar@permabit.com>]

Peter Staubach <staubach@redhat.com> writes:
> Understand.  I would recommend that the 2.4 kernel be modified to return
> an error, since we are already modifying the area anyway.

Marcelo: what's your thought?

If you want to go that route, the patch below should do it.

diff -u linux-2.4.31.orig/fs/nfs/nfs2xdr.c linux-2.4.31/fs/nfs/nfs2xdr.c
--- linux-2.4.31.orig/fs/nfs/nfs2xdr.c	2002-11-28 18:53:15.000000000 -0500
+++ linux-2.4.31/fs/nfs/nfs2xdr.c	2005-09-14 16:57:21.000000000 -0400
@@ -571,8 +571,11 @@
 	strlen = (u32*)kmap(rcvbuf->pages[0]);
 	/* Convert length of symlink */
 	len = ntohl(*strlen);
-	if (len > rcvbuf->page_len)
-		len = rcvbuf->page_len;
+	if (len >= rcvbuf->page_len - sizeof(u32) || len > NFS2_MAXPATHLEN) {
+		printk(KERN_WARNING "NFS: server returned giant symlink!\n");
+		kunmap(rcvbuf->pages[0]);
+		return -ENAMETOOLONG;
+        }
 	*strlen = len;
 	/* NULL terminate the string we got */
 	string = (char *)(strlen + 1);
diff -u linux-2.4.31.orig/fs/nfs/nfs3xdr.c linux-2.4.31/fs/nfs/nfs3xdr.c
--- linux-2.4.31.orig/fs/nfs/nfs3xdr.c	2003-11-28 13:26:21.000000000 -0500
+++ linux-2.4.31/fs/nfs/nfs3xdr.c	2005-09-14 16:57:37.000000000 -0400
@@ -759,8 +759,11 @@
 	strlen = (u32*)kmap(rcvbuf->pages[0]);
 	/* Convert length of symlink */
 	len = ntohl(*strlen);
-	if (len > rcvbuf->page_len)
-		len = rcvbuf->page_len;
+	if (len >= rcvbuf->page_len - sizeof(u32)) {
+		printk(KERN_WARNING "NFS: server returned giant symlink!\n");
+		kunmap(rcvbuf->pages[0]);
+		return -ENAMETOOLONG;
+        }
 	*strlen = len;
 	/* NULL terminate the string we got */
 	string = (char *)(strlen + 1);