On Sun, Jul 08, 2012 at 09:50:43PM +0200, Eric Dumazet wrote:
> On Thu, 2012-07-05 at 17:28 +0800, Gao feng wrote:
> > we set max_prioidx to the first zero bit index of prioidx_map in
> > function get_prioidx.
> >
> > So when we delete the low index netprio cgroup and adding a new
> > netprio cgroup again,the max_prioidx will be set to the low index.
> >
> > when we set the high index cgroup's net_prio.ifpriomap,the function
> > write_priomap will call update_netdev_tables to alloc memory which
> > size is sizeof(struct netprio_map) + sizeof(u32) * (max_prioidx + 1),
> > so the size of array that map->priomap point to is max_prioidx +1,
> > which is low than what we actually need.
> >
> > fix this by adding check in get_prioidx,only set max_prioidx when
> > max_prioidx low than the new prioidx.
> >
> > Signed-off-by: Gao feng <gaof...@cn.fujitsu.com>
> > ---
> > net/core/netprio_cgroup.c | 3 ++-
> > 1 files changed, 2 insertions(+), 1 deletions(-)
> >
> > diff --git a/net/core/netprio_cgroup.c b/net/core/netprio_cgroup.c
> > index 5b8aa2f..aa907ed 100644
> > --- a/net/core/netprio_cgroup.c
> > +++ b/net/core/netprio_cgroup.c
> > @@ -49,8 +49,9 @@ static int get_prioidx(u32 *prio)
> > return -ENOSPC;
> > }
> > set_bit(prioidx, prioidx_map);
> > + if (atomic_read(&max_prioidx) < prioidx)
> > + atomic_set(&max_prioidx, prioidx);
> > spin_unlock_irqrestore(&prioidx_map_lock, flags);
> > - atomic_set(&max_prioidx, prioidx);
> > *prio = prioidx;
> > return 0;
> > }
>
> This patch seems fine to me.
>
> Acked-by: Eric Dumazet <eduma...@google.com>
>
> Neil, looking at this file, I believe something is wrong.
>
> dev->priomap is allocated by extend_netdev_table() called from
> update_netdev_tables(). And this is only called if write_priomap() is
> called.
>
> But if write_priomap() is not called, it seems we can have out of bounds
> accesses in cgrp_destroy() and read_priomap()
>
> What do you think of following patch ?
>
> diff --git a/net/core/netprio_cgroup.c b/net/core/netprio_cgroup.c
> index 5b8aa2f..80150d2 100644
> --- a/net/core/netprio_cgroup.c
> +++ b/net/core/netprio_cgroup.c
> @@ -141,7 +141,7 @@ static void cgrp_destroy(struct cgroup *cgrp)
> rtnl_lock();
> for_each_netdev(&init_net, dev) {
> map = rtnl_dereference(dev->priomap);
> - if (map)
> + if (map && cs->prioidx < map->priomap_len)
> map->priomap[cs->prioidx] = 0;
> }
> rtnl_unlock();
> @@ -165,7 +165,7 @@ static int read_priomap(struct cgroup *cont, struct
> cftype *cft,
> rcu_read_lock();
> for_each_netdev_rcu(&init_net, dev) {
> map = rcu_dereference(dev->priomap);
> - priority = map ? map->priomap[prioidx] : 0;
> + priority = (map && prioidx < map->priomap_len) ?
> map->priomap[prioidx] : 0;
> cb->fill(cb, dev->name, priority);
> }
> rcu_read_unlock();
>
>
>
You're right, If we create a cgroup after a net device is registered the group
priority index will likely be out of bounds for those devices. We can fix it
like you propose above (including the additional prioidx < map->priomap_len
check in skb_update_prio as Gao notes), or we can call update_netdev_tables
iteratively for every net device in cgrp_create, and on device_registration in
netprio_device_event.
I'm not sure how adventageous one is over the other, but it does seem that,
given that skb_update_prio is in the transmit path, it might be nice to avoid
the additional length check there if possible.
Thanks!
Neil
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