linux-kernel - Re: [patch] relay: prevent integer overflow in relay

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Date:	Thu, 09 Feb 2012 12:55:52 +0100
From:	walter harms <wharms@....de>
To:	Dan Carpenter <dan.carpenter@...cle.com>
CC:	Jens Axboe <axboe@...nel.dk>,
	Paul Gortmaker <paul.gortmaker@...driver.com>,
	Al Viro <viro@...iv.linux.org.uk>,
	linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org
Subject: Re: [patch] relay: prevent integer overflow in relay_open()



Am 09.02.2012 11:44, schrieb Dan Carpenter:
> "subbuf_size" and "n_subbufs" come from the user and they need to be
> capped to prevent an integer overflow.
> 
> Signed-off-by: Dan Carpenter <dan.carpenter@...cle.com>
> 
> diff --git a/kernel/relay.c b/kernel/relay.c
> index 4335e1d..ab56a17 100644
> --- a/kernel/relay.c
> +++ b/kernel/relay.c
> @@ -164,10 +164,14 @@ depopulate:
>   */
>  static struct rchan_buf *relay_create_buf(struct rchan *chan)
>  {
> -	struct rchan_buf *buf = kzalloc(sizeof(struct rchan_buf), GFP_KERNEL);
> -	if (!buf)
> +	struct rchan_buf *buf;
> +
> +	if (chan->n_subbufs > UINT_MAX / sizeof(size_t *))
>  		return NULL;
>  
> +	buf = kzalloc(sizeof(struct rchan_buf), GFP_KERNEL);
> +	if (!buf)
> +		return NULL;
>  	buf->padding = kmalloc(chan->n_subbufs * sizeof(size_t *), GFP_KERNEL);
>  	if (!buf->padding)
>  		goto free_buf;
> @@ -574,6 +578,8 @@ struct rchan *relay_open(const char *base_filename,
>  
>  	if (!(subbuf_size && n_subbufs))
>  		return NULL;
> +	if (subbuf_size > UINT_MAX / n_subbufs)
> +		return NULL;
>  
>  	chan = kzalloc(sizeof(struct rchan), GFP_KERNEL);
>  	if (!chan)
> --


numerical this is ok, but ...
maybe it is better to cap the chan->n_subbufs at a useful number ?
The user can still allocate an insane number of bytes.
Restricting subbuf_size*n_subbufs seems more logical (otherwise is this a real problem ?)

re,
 wh
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