Subject: Re: [PATCH v4] net: cgroup: fix access the unallocated memory in netprio cgroup

From: John Fastabend <[email-masked]>
Date: Tue, 17 Jul 2012 13:47:25 -0700

On 7/12/2012 12:50 AM, Gao feng wrote:
> there are some out of bound accesses in netprio cgroup.
>
> now before accessing the dev->priomap.priomap array,we only check
> if the dev->priomap exist.and because we don't want to see
> additional bound checkings in fast path, so we should make sure
> that dev->priomap is null or array size of dev->priomap.priomap
> is equal to max_prioidx + 1;
>
> so in write_priomap logic,we should call extend_netdev_table when
> dev->priomap is null and dev->priomap.priomap_len < max_len.
> and in cgrp_create->update_netdev_tables logic,we should call
> extend_netdev_table only when dev->priomap exist and
> dev->priomap.priomap_len < max_len.
>
> and it's not needed to call update_netdev_tables in write_priomap,
> we can only allocate the net device's priomap which we change through
> net_prio.ifpriomap.
>
> this patch also add a return value for update_netdev_tables &
> extend_netdev_table, so when new_priomap is allocated failed,
> write_priomap will stop to access the priomap,and return -ENOMEM
> back to the userspace to tell the user what happend.
>
> Change From v3:
> 1. add rtnl protect when reading max_prioidx in write_priomap.
>
> 2. only call extend_netdev_table when map->priomap_len < max_len,
>     this will make sure array size of dev->map->priomap always
>     bigger than any prioidx.
>
> 3. add a function write_update_netdev_table to make codes clear.
>
> Change From v2:
> 1. protect extend_netdev_table by RTNL.
> 2. when extend_netdev_table failed,call dev_put to reduce device's refcount.
>
> Signed-off-by: Gao feng <[email-masked]>
> Cc: Neil Horman <[email-masked]>
> Cc: Eric Dumazet <[email-masked]>
> ---
>   net/core/netprio_cgroup.c |   71 ++++++++++++++++++++++++++++++++++-----------
>   1 files changed, 54 insertions(+), 17 deletions(-)
>

[...]

> +
> +static int update_netdev_tables(void)
> +{
> +	int ret = 0;
>   	struct net_device *dev;
> -	u32 max_len = atomic_read(&max_prioidx) + 1;
> +	u32 max_len;
>   	struct netprio_map *map;

need to check if net subsystem is initialized before we try
to use it here...

	if (some_check)     -> need to lookup what this check is
		return ret;

>
>   	rtnl_lock();
> +	max_len = atomic_read(&max_prioidx) + 1;
>   	for_each_netdev(&init_net, dev) {
>   		map = rtnl_dereference(dev->priomap);
> -		if ((!map) ||
> -		    (map->priomap_len < max_len))
> -			extend_netdev_table(dev, max_len);
> +		/*
> +		 * don't allocate priomap if we didn't
> +		 * change net_prio.ifpriomap (map == NULL),
> +		 * this will speed up skb_update_prio.
> +		 */
> +		if (map && map->priomap_len < max_len) {
> +			ret = extend_netdev_table(dev, max_len);
> +			if (ret < 0)
> +				break;
> +		}
>   	}
>   	rtnl_unlock();
> +	return ret;
>   }
>
>   static struct cgroup_subsys_state *cgrp_create(struct cgroup *cgrp)
>   {
>   	struct cgroup_netprio_state *cs;
> -	int ret;
> +	int ret = -EINVAL;
>
>   	cs = kzalloc(sizeof(*cs), GFP_KERNEL);
>   	if (!cs)
>   		return ERR_PTR(-ENOMEM);
>
> -	if (cgrp->parent && cgrp_netprio_state(cgrp->parent)->prioidx) {
> -		kfree(cs);
> -		return ERR_PTR(-EINVAL);
> -	}
> +	if (cgrp->parent && cgrp_netprio_state(cgrp->parent)->prioidx)
> +		goto out;
>
>   	ret = get_prioidx(&cs->prioidx);
> -	if (ret != 0) {
> +	if (ret < 0) {
>   		pr_warn("No space in priority index array\n");
> -		kfree(cs);
> -		return ERR_PTR(ret);
> +		goto out;
> +	}
> +
> +	ret = update_netdev_tables();
> +	if (ret < 0) {
> +		put_prioidx(cs->prioidx);
> +		goto out;
>   	}

Gao,

This introduces a null ptr dereference when netprio_cgroup is built
into the kernel because update_netdev_tables() depends on init_net.
However cgrp_create is being called by cgroup_init before
do_initcalls() is called and before net_dev_init().

.John