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

[Assar <assar@permabit.com>]

Valdis.Kletnieks@vt.edu writes:
> > To my reading, the 2.6.13 code does not copy the 4 bytes of length to
> > rcvbuf.
> 
> Hmm... it still does this:
> 	kaddr[len+rcvbuf->page_base] = '\0';
> which still has a possible off-by-one? (Was that why you have -1 -4?)

The check is different.  2.6.13 is using ">=" instead of ">", so hence
I think that's fine.

> sizeof(actual_var) is even better, as that way it's clear what you're allowing
> space for.

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	2005-09-12 16:12:30.000000000 -0400
@@ -571,8 +571,8 @@
 	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(*strlen) - 1)
+		len = rcvbuf->page_len - sizeof(*strlen) - 1;
 	*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	2005-09-12 16:12:29.000000000 -0400
@@ -759,8 +759,8 @@
 	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(*strlen) - 1)
+		len = rcvbuf->page_len - sizeof(*strlen) - 1;
 	*strlen = len;
 	/* NULL terminate the string we got */
 	string = (char *)(strlen + 1);