linux-kernel - Re: [PATCH] NFS4: Avoid potential NULL pointer dereference in decode_and_add

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Date:	Mon, 17 Jan 2011 12:04:29 -0500
From:	Fred Isaman <iisaman@...app.com>
To:	Jesper Juhl <jj@...osbits.net>
Cc:	linux-nfs@...r.kernel.org,
	Trond Myklebust <Trond.Myklebust@...app.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] NFS4: Avoid potential NULL pointer dereference in decode_and_add_ds().

On Sun, Jan 16, 2011 at 3:50 PM, Jesper Juhl <jj@...osbits.net> wrote:
> strrchr() can return NULL if nothing is found. If this happens we'll
> dereference a NULL pointer in
> fs/nfs/nfs4filelayoutdev.c::decode_and_add_ds().
>
> I tried to find some other code that guarantees that this can never
> happen but I was unsuccessful. So, unless someone else can point to some
> code that ensures this can never be a problem, I believe this patch is
> needed.
>

The only guarantee is the assumption that the server isn't sending
garbage.  As such, this patch looks good to me.

Fred

> While I was changing this code I also noticed that all the dprintk()
> statements, except one, start with "%s:". The one missing the ":" I added
> it to.
>
> Signed-off-by: Jesper Juhl <jj@...osbits.net>
> ---
>  nfs4filelayoutdev.c |    7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
>
>  only compile tested.
>
> diff --git a/fs/nfs/nfs4filelayoutdev.c b/fs/nfs/nfs4filelayoutdev.c
> index 51fe64a..5a85b8f 100644
> --- a/fs/nfs/nfs4filelayoutdev.c
> +++ b/fs/nfs/nfs4filelayoutdev.c
> @@ -214,7 +214,7 @@ decode_and_add_ds(__be32 **pp, struct inode *inode)
>
>        /* ipv6 length plus port is legal */
>        if (rlen > INET6_ADDRSTRLEN + 8) {
> -               dprintk("%s Invalid address, length %d\n", __func__,
> +               dprintk("%s: Invalid address, length %d\n", __func__,
>                        rlen);
>                goto out_err;
>        }
> @@ -225,6 +225,11 @@ decode_and_add_ds(__be32 **pp, struct inode *inode)
>        /* replace the port dots with dashes for the in4_pton() delimiter*/
>        for (i = 0; i < 2; i++) {
>                char *res = strrchr(buf, '.');
> +               if (!res) {
> +                       dprintk("%s: Failed finding expected dots in port\n",
> +                               __func__);
> +                       goto out_free;
> +               }
>                *res = '-';
>        }
>
>
> --
> Jesper Juhl <jj@...osbits.net>            http://www.chaosbits.net/
> Don't top-post http://www.catb.org/~esr/jargon/html/T/top-post.html
> Plain text mails only, please.
>
> --
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