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

[Valdis.Kletnieks@vt.edu]

On Mon, 12 Sep 2005 09:26:28 EDT, Assar said:
> In 2.4.31, the v2/3 nfs readlink accepts too long symlinks.
> I have tested this by having a server return long symlinks.
> 2.6.13 does not to my reading have this problem.

Odd, as it has similar code - 2.6.13-mm1 nfs2xdr.c has:
        /* Convert length of symlink */
        len = ntohl(*p++);
        if (len >= rcvbuf->page_len || len <= 0) {

Is there some *other* code in 2.6 that prevents this from being a problem,
if it's a problem on 2.4?

> 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	2005-09-07 17:36:04.000000000 -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 - 1 - 4)
> +		len = rcvbuf->page_len - 1 - 4;

Am I the only one who finds an uncommented "-1 -4" construct scary beyond belief?

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