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net: add networking namespace refcount tracker

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We have 100+ syzbot reports about netns being dismantled too soon,
still unresolved as of today.

We think a missing get_net() or an extra put_net() is the root cause.

In order to find the bug(s), and be able to spot future ones,
this patch adds CONFIG_NET_NS_REFCNT_TRACKER and new helpers
to precisely pair all put_net() with corresponding get_net().

To use these helpers, each data structure owning a refcount
should also use a "netns_tracker" to pair the get and put.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Eric Dumazet 2021-12-09 23:44:21 -08:00 committed by Jakub Kicinski
parent e5d75fc20b
commit 9ba74e6c9e
5 changed files with 65 additions and 8 deletions
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9
include/linux/netdevice.h
View File

@ -48,7 +48,7 @@
#include <uapi/linux/pkt_cls.h>
#include <linux/hashtable.h>
#include <linux/rbtree.h>
#include <linux/ref_tracker.h>
#include <net/net_trackers.h>
struct netpoll_info;
struct device;
@ -300,13 +300,6 @@ enum netdev_state_t {
__LINK_STATE_TESTING,
};
#ifdef CONFIG_NET_DEV_REFCNT_TRACKER
typedef struct ref_tracker *netdevice_tracker;
#else
typedef struct {} netdevice_tracker;
#endif
struct gro_list {
struct list_head list;
int count;

34
include/net/net_namespace.h
View File

@ -34,6 +34,7 @@
#include <net/netns/smc.h>
#include <net/netns/bpf.h>
#include <net/netns/mctp.h>
#include <net/net_trackers.h>
#include <linux/ns_common.h>
#include <linux/idr.h>
#include <linux/skbuff.h>
@ -87,6 +88,7 @@ struct net {
struct idr netns_ids;
struct ns_common ns;
struct ref_tracker_dir refcnt_tracker;
struct list_head dev_base_head;
struct proc_dir_entry *proc_net;
@ -240,6 +242,7 @@ void ipx_unregister_sysctl(void);
#ifdef CONFIG_NET_NS
void __put_net(struct net *net);
/* Try using get_net_track() instead */
static inline struct net *get_net(struct net *net)
{
refcount_inc(&net->ns.count);
@ -258,6 +261,7 @@ static inline struct net *maybe_get_net(struct net *net)
return net;
}
/* Try using put_net_track() instead */
static inline void put_net(struct net *net)
{
if (refcount_dec_and_test(&net->ns.count))
@ -308,6 +312,36 @@ static inline int check_net(const struct net *net)
#endif
static inline void netns_tracker_alloc(struct net *net,
netns_tracker *tracker, gfp_t gfp)
{
#ifdef CONFIG_NET_NS_REFCNT_TRACKER
ref_tracker_alloc(&net->refcnt_tracker, tracker, gfp);
#endif
}
static inline void netns_tracker_free(struct net *net,
netns_tracker *tracker)
{
#ifdef CONFIG_NET_NS_REFCNT_TRACKER
ref_tracker_free(&net->refcnt_tracker, tracker);
#endif
}
static inline struct net *get_net_track(struct net *net,
netns_tracker *tracker, gfp_t gfp)
{
get_net(net);
netns_tracker_alloc(net, tracker, gfp);
return net;
}
static inline void put_net_track(struct net *net, netns_tracker *tracker)
{
netns_tracker_free(net, tracker);
put_net(net);
}
typedef struct {
#ifdef CONFIG_NET_NS
struct net *net;

18
include/net/net_trackers.h Normal file
View File

@ -0,0 +1,18 @@
/* SPDX-License-Identifier: GPL-2.0 */
#ifndef __NET_NET_TRACKERS_H
#define __NET_NET_TRACKERS_H
#include <linux/ref_tracker.h>
#ifdef CONFIG_NET_DEV_REFCNT_TRACKER
typedef struct ref_tracker *netdevice_tracker;
#else
typedef struct {} netdevice_tracker;
#endif
#ifdef CONFIG_NET_NS_REFCNT_TRACKER
typedef struct ref_tracker *netns_tracker;
#else
typedef struct {} netns_tracker;
#endif
#endif /* __NET_NET_TRACKERS_H */

9
net/Kconfig.debug
View File

@ -8,3 +8,12 @@ config NET_DEV_REFCNT_TRACKER
help
Enable debugging feature to track device references.
This adds memory and cpu costs.
config NET_NS_REFCNT_TRACKER
bool "Enable networking namespace refcount tracking"
depends on DEBUG_KERNEL && STACKTRACE_SUPPORT
select REF_TRACKER
default n
help
Enable debugging feature to track netns references.
This adds memory and cpu costs.

3
net/core/net_namespace.c
View File

@ -311,6 +311,8 @@ static __net_init int setup_net(struct net *net, struct user_namespace *user_ns)
LIST_HEAD(net_exit_list);
refcount_set(&net->ns.count, 1);
ref_tracker_dir_init(&net->refcnt_tracker, 128);
refcount_set(&net->passive, 1);
get_random_bytes(&net->hash_mix, sizeof(u32));
preempt_disable();
@ -635,6 +637,7 @@ static DECLARE_WORK(net_cleanup_work, cleanup_net);
void __put_net(struct net *net)
{
ref_tracker_dir_exit(&net->refcnt_tracker);
/* Cleanup the network namespace in process context */
if (llist_add(&net->cleanup_list, &cleanup_list))
queue_work(netns_wq, &net_cleanup_work);