linux-kernel - Re: [PATCH] nfsd: avoid out of bounds read on array nfsd4_layout

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Message-ID: <20170509140414.ycw4z6zsdevbkozm@mwanda>
Date:   Tue, 9 May 2017 17:04:14 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     Colin King <colin.king@...onical.com>
Cc:     Ari Kauppi <ari@...opsys.com>,
        "J . Bruce Fields" <bfields@...ldses.org>,
        Jeff Layton <jlayton@...chiereds.net>,
        linux-nfs@...r.kernel.org, kernel-janitors@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] nfsd: avoid out of bounds read on array nfsd4_layout_ops

On Tue, May 09, 2017 at 02:31:21PM +0100, Colin King wrote:
> diff --git a/fs/nfsd/nfs4proc.c b/fs/nfsd/nfs4proc.c
> index 1dbf62190bee..c453a1998e00 100644
> --- a/fs/nfsd/nfs4proc.c
> +++ b/fs/nfsd/nfs4proc.c
> @@ -1259,7 +1259,8 @@ nfsd4_layout_verify(struct svc_export *exp, unsigned int layout_type)
>  		return NULL;
>  	}
>  
> -	if (layout_type >= 32 || !(exp->ex_layout_types & (1 << layout_type))) {
> +	if (layout_type >= LAYOUT_TYPE_MAX ||
> +	    !(exp->ex_layout_types & (1 << layout_type))) {

The 32 is there to prevent a shift wrapping bug.  The bit test prevents
a buffer overflow so this can't actually overflow.  But this change
doesn't hurt and is probably cleaner.

exp->ex_layout_types  is set in nfsd4_setup_layout_type().

regards,
dan carpenter