Messages in this thread | | | Date | Wed, 18 Jul 2012 07:10:18 -0700 | From | John Fastabend <> | Subject | Re: [PATCH v4] net: cgroup: fix access the unallocated memory in netprio cgroup |
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On 7/18/2012 5:21 AM, Neil Horman wrote: > On Tue, Jul 17, 2012 at 01:47:25PM -0700, John Fastabend wrote: >> 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 <gaofeng@cn.fujitsu.com> >>> Cc: Neil Horman <nhorman@tuxdriver.com> >>> Cc: Eric Dumazet <edumazet@google.com> >>> --- >>> 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 >> > Not sure I follow here John. Shouldn't init_net be initialized prior to any > network devices getting registered? In other words, shouldn't for_each_netdev > just result in zero iterations through the loop? > Neil >
init_net _is_ initialized prior to any network devices getting registered but not before cgrp_create called via cgroup_init.
#define for_each_netdev(net, d) \ list_for_each_entry(d, &(net)->dev_base_head, dev_list)
but dev_base_head is zeroed at this time. In netdev_init we have,
INIT_LIST_HEAD(&net->dev_base_head);
but we haven't got that far yet because cgroup_init is called before do_initcalls().
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