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Date: Wed, 24 Apr 2019 04:38:09 -0700
From: Eric Dumazet <eric.dumazet@...il.com>
To: Florian Westphal <fw@...len.de>, vakul.garg@....com
Cc: steffen.klassert@...unet.com, netdev@...r.kernel.org
Subject: Re: [RFC HACK] xfrm: make state refcounting percpu
On 04/24/2019 03:40 AM, Florian Westphal wrote:
> I'm not sure this is a good idea to begin with, refcount
> is right next to state spinlock which is taken for both tx and rx ops,
> plus this complicates debugging quite a bit.
>
Why not simply using include/linux/percpu-refcount.h ?
> Also expect UAF or refcount bugs, especially xfrm_states that won't get free'd.
>
> In case someone wants to experiment with this, I've placed it here:
> https://git.breakpoint.cc/cgit/fw/net-next.git/log/?h=xfrm_pcpu_gc_04
>
> Summary of old/new locking model:
>
> Old locking rules:
> From control plane:
> - new states get refcount of 1
> - calls xfrm_state_put() when done
> - calls xfrm_state_hold() to make sure
> state won't go away
>
> From data plane:
> - calls xfrm_state_hold_rcu, which will tell when
> refcount is already 0 (i.e, state is being destroyed)
> - calls xfrm_state_put when done
>
> From gc worker:
> - steals current gc list head
> - call synchronize_rcu
> - can free all entries in the list after this
>
> Last xfrm_state_put will observe refcount transition to 0,
> this will place xfrm_state on gc list, where its picked
> up (and free'd) by xfrm state gc worker.
>
> New locking rules:
> From control plane:
> - (NEW) must *explicitly* call xfrm_state_delete()
> when state should be removed
> - otherwise same as above
> From data plane:
> - calls xfrm_state_hold() to get ref,
> xfrm_state_put when done
> From gc worker:
> - steals current gc list head
> - call synchronize_rcu
> - entries on list MAY STILL BE IN USE, so
> * must check refcount for each (expensive, as it
> summing pcpu refcounts for each state)
> * needs to place entries that it can't free yet
> back on gc list and resched itself
>
> XXX:
> - survives minimal testing (netns + veth + esp tunnel mode)
> - refcount for newly allocated states should probably be
> changed to 0, and only do 0 -> 1 increment right before
> state is published (added to state hashes).
> - probably misses several error handling spots that now would
> have to call xfrm_state_delete() rather than xfrm_state_put().
>
> Signed-off-by: Florian Westphal <fw@...len.de>
> ---
> include/net/xfrm.h | 20 ++--------
> net/key/af_key.c | 4 +-
> net/xfrm/xfrm_state.c | 90 ++++++++++++++++++++++++-------------------
> net/xfrm/xfrm_user.c | 2 +-
> 4 files changed, 57 insertions(+), 59 deletions(-)
>
> diff --git a/include/net/xfrm.h b/include/net/xfrm.h
> index 728d4e7b82c0..f9be94a3a029 100644
> --- a/include/net/xfrm.h
> +++ b/include/net/xfrm.h
> @@ -153,7 +153,7 @@ struct xfrm_state {
> struct hlist_node bysrc;
> struct hlist_node byspi;
>
> - refcount_t refcnt;
> + int __percpu *pcpu_refcnt;
> spinlock_t lock;
>
> struct xfrm_id id;
> @@ -790,26 +790,14 @@ static inline void xfrm_pols_put(struct xfrm_policy **pols, int npols)
>
> void __xfrm_state_destroy(struct xfrm_state *, bool);
>
> -static inline void __xfrm_state_put(struct xfrm_state *x)
> +static inline void xfrm_state_hold(struct xfrm_state *x)
> {
> - refcount_dec(&x->refcnt);
> + this_cpu_inc(*x->pcpu_refcnt);
> }
>
> static inline void xfrm_state_put(struct xfrm_state *x)
> {
> - if (refcount_dec_and_test(&x->refcnt))
> - __xfrm_state_destroy(x, false);
> -}
> -
> -static inline void xfrm_state_put_sync(struct xfrm_state *x)
> -{
> - if (refcount_dec_and_test(&x->refcnt))
> - __xfrm_state_destroy(x, true);
> -}
> -
> -static inline void xfrm_state_hold(struct xfrm_state *x)
> -{
> - refcount_inc(&x->refcnt);
> + this_cpu_dec(*x->pcpu_refcnt);
> }
>
> static inline bool addr_match(const void *token1, const void *token2,
> diff --git a/net/key/af_key.c b/net/key/af_key.c
> index 5651c29cb5bd..21d4776b5431 100644
> --- a/net/key/af_key.c
> +++ b/net/key/af_key.c
> @@ -1303,7 +1303,7 @@ static struct xfrm_state * pfkey_msg2xfrm_state(struct net *net,
>
> out:
> x->km.state = XFRM_STATE_DEAD;
> - xfrm_state_put(x);
> + xfrm_state_delete(x);
> return ERR_PTR(err);
> }
>
> @@ -1525,7 +1525,7 @@ static int pfkey_add(struct sock *sk, struct sk_buff *skb, const struct sadb_msg
>
> if (err < 0) {
> x->km.state = XFRM_STATE_DEAD;
> - __xfrm_state_put(x);
> + xfrm_state_delete(x);
> goto out;
> }
>
> diff --git a/net/xfrm/xfrm_state.c b/net/xfrm/xfrm_state.c
> index 8951c09ae9e9..4614df21ff5c 100644
> --- a/net/xfrm/xfrm_state.c
> +++ b/net/xfrm/xfrm_state.c
> @@ -31,6 +31,8 @@
> #define xfrm_state_deref_prot(table, net) \
> rcu_dereference_protected((table), lockdep_is_held(&(net)->xfrm.xfrm_state_lock))
>
> +#define XFRM_GC_WAIT_JIFFIES 2
> +
> static void xfrm_state_gc_task(struct work_struct *work);
>
> /* Each xfrm_state may be linked to two tables:
> @@ -44,14 +46,9 @@ static unsigned int xfrm_state_hashmax __read_mostly = 1 * 1024 * 1024;
> static __read_mostly seqcount_t xfrm_state_hash_generation = SEQCNT_ZERO(xfrm_state_hash_generation);
> static struct kmem_cache *xfrm_state_cache __ro_after_init;
>
> -static DECLARE_WORK(xfrm_state_gc_work, xfrm_state_gc_task);
> +static DECLARE_DELAYED_WORK(xfrm_state_gc_work, xfrm_state_gc_task);
> static HLIST_HEAD(xfrm_state_gc_list);
>
> -static inline bool xfrm_state_hold_rcu(struct xfrm_state __rcu *x)
> -{
> - return refcount_inc_not_zero(&x->refcnt);
> -}
> -
> static inline unsigned int xfrm_dst_hash(struct net *net,
> const xfrm_address_t *daddr,
> const xfrm_address_t *saddr,
> @@ -472,6 +469,7 @@ static const struct xfrm_mode *xfrm_get_mode(unsigned int encap, int family)
>
> void xfrm_state_free(struct xfrm_state *x)
> {
> + free_percpu(x->pcpu_refcnt);
> kmem_cache_free(xfrm_state_cache, x);
> }
> EXPORT_SYMBOL(xfrm_state_free);
> @@ -499,6 +497,15 @@ static void ___xfrm_state_destroy(struct xfrm_state *x)
> xfrm_state_free(x);
> }
>
> +static int xfrm_state_refcnt_read(const struct xfrm_state *x)
> +{
> + int i, refcnt = 0;
> +
> + for_each_possible_cpu(i)
> + refcnt += *per_cpu_ptr(x->pcpu_refcnt, i);
> + return refcnt;
> +}
> +
> static void xfrm_state_gc_task(struct work_struct *work)
> {
> struct xfrm_state *x;
> @@ -511,8 +518,22 @@ static void xfrm_state_gc_task(struct work_struct *work)
>
> synchronize_rcu();
>
> - hlist_for_each_entry_safe(x, tmp, &gc_list, gclist)
> + hlist_for_each_entry_safe(x, tmp, &gc_list, gclist) {
> + if (xfrm_state_refcnt_read(x))
> + continue;
> +
> + hlist_del(&x->gclist);
> ___xfrm_state_destroy(x);
> + }
> +
> + if (!hlist_empty(&gc_list)) {
> + spin_lock_bh(&xfrm_state_gc_lock);
> + hlist_for_each_entry_safe(x, tmp, &gc_list, gclist)
> + hlist_add_head(&x->gclist, &xfrm_state_gc_list);
> + spin_unlock_bh(&xfrm_state_gc_lock);
> +
> + schedule_delayed_work(&xfrm_state_gc_work, XFRM_GC_WAIT_JIFFIES);
> + }
> }
>
> static enum hrtimer_restart xfrm_timer_handler(struct hrtimer *me)
> @@ -611,8 +632,14 @@ struct xfrm_state *xfrm_state_alloc(struct net *net)
> x = kmem_cache_alloc(xfrm_state_cache, GFP_ATOMIC | __GFP_ZERO);
>
> if (x) {
> + x->pcpu_refcnt = alloc_percpu(int);
> + if (!x->pcpu_refcnt) {
> + kmem_cache_free(xfrm_state_cache, x);
> + return NULL;
> + }
> +
> write_pnet(&x->xs_net, net);
> - refcount_set(&x->refcnt, 1);
> + xfrm_state_hold(x);
> atomic_set(&x->tunnel_users, 0);
> INIT_LIST_HEAD(&x->km.all);
> INIT_HLIST_NODE(&x->bydst);
> @@ -634,22 +661,6 @@ struct xfrm_state *xfrm_state_alloc(struct net *net)
> }
> EXPORT_SYMBOL(xfrm_state_alloc);
>
> -void __xfrm_state_destroy(struct xfrm_state *x, bool sync)
> -{
> - WARN_ON(x->km.state != XFRM_STATE_DEAD);
> -
> - if (sync) {
> - synchronize_rcu();
> - ___xfrm_state_destroy(x);
> - } else {
> - spin_lock_bh(&xfrm_state_gc_lock);
> - hlist_add_head(&x->gclist, &xfrm_state_gc_list);
> - spin_unlock_bh(&xfrm_state_gc_lock);
> - schedule_work(&xfrm_state_gc_work);
> - }
> -}
> -EXPORT_SYMBOL(__xfrm_state_destroy);
> -
> int __xfrm_state_delete(struct xfrm_state *x)
> {
> struct net *net = xs_net(x);
> @@ -673,6 +684,12 @@ int __xfrm_state_delete(struct xfrm_state *x)
> * is what we are dropping here.
> */
> xfrm_state_put(x);
> +
> + spin_lock_bh(&xfrm_state_gc_lock);
> + hlist_add_head(&x->gclist, &xfrm_state_gc_list);
> + spin_unlock_bh(&xfrm_state_gc_lock);
> +
> + schedule_delayed_work(&xfrm_state_gc_work, 0);
> err = 0;
> }
>
> @@ -771,10 +788,7 @@ int xfrm_state_flush(struct net *net, u8 proto, bool task_valid, bool sync)
> err = xfrm_state_delete(x);
> xfrm_audit_state_delete(x, err ? 0 : 1,
> task_valid);
> - if (sync)
> - xfrm_state_put_sync(x);
> - else
> - xfrm_state_put(x);
> + xfrm_state_put(x);
> if (!err)
> cnt++;
>
> @@ -937,8 +951,8 @@ static struct xfrm_state *__xfrm_state_lookup(struct net *net, u32 mark,
>
> if ((mark & x->mark.m) != x->mark.v)
> continue;
> - if (!xfrm_state_hold_rcu(x))
> - continue;
> +
> + xfrm_state_hold(x);
> return x;
> }
>
> @@ -962,8 +976,7 @@ static struct xfrm_state *__xfrm_state_lookup_byaddr(struct net *net, u32 mark,
>
> if ((mark & x->mark.m) != x->mark.v)
> continue;
> - if (!xfrm_state_hold_rcu(x))
> - continue;
> + xfrm_state_hold(x);
> return x;
> }
>
> @@ -1151,10 +1164,7 @@ xfrm_state_find(const xfrm_address_t *daddr, const xfrm_address_t *saddr,
> }
> out:
> if (x) {
> - if (!xfrm_state_hold_rcu(x)) {
> - *err = -EAGAIN;
> - x = NULL;
> - }
> + xfrm_state_hold(x);
> } else {
> *err = acquire_in_progress ? -EAGAIN : error;
> }
> @@ -1681,7 +1691,7 @@ int xfrm_state_update(struct xfrm_state *x)
>
> err = 0;
> x->km.state = XFRM_STATE_DEAD;
> - __xfrm_state_put(x);
> + xfrm_state_put(x);
> }
>
> fail:
> @@ -2372,7 +2382,7 @@ struct xfrm_state_afinfo *xfrm_state_get_afinfo(unsigned int family)
>
> void xfrm_flush_gc(void)
> {
> - flush_work(&xfrm_state_gc_work);
> + flush_delayed_work(&xfrm_state_gc_work);
> }
> EXPORT_SYMBOL(xfrm_flush_gc);
>
> @@ -2385,7 +2395,7 @@ void xfrm_state_delete_tunnel(struct xfrm_state *x)
> if (atomic_read(&t->tunnel_users) == 2)
> xfrm_state_delete(t);
> atomic_dec(&t->tunnel_users);
> - xfrm_state_put_sync(t);
> + xfrm_state_put(t);
> x->tunnel = NULL;
> }
> }
> @@ -2531,7 +2541,7 @@ void xfrm_state_fini(struct net *net)
> unsigned int sz;
>
> flush_work(&net->xfrm.state_hash_work);
> - flush_work(&xfrm_state_gc_work);
> + flush_delayed_work(&xfrm_state_gc_work);
> xfrm_state_flush(net, IPSEC_PROTO_ANY, false, true);
>
> WARN_ON(!list_empty(&net->xfrm.state_all));
> diff --git a/net/xfrm/xfrm_user.c b/net/xfrm/xfrm_user.c
> index a131f9ff979e..4587f1342af0 100644
> --- a/net/xfrm/xfrm_user.c
> +++ b/net/xfrm/xfrm_user.c
> @@ -675,7 +675,7 @@ static int xfrm_add_sa(struct sk_buff *skb, struct nlmsghdr *nlh,
> if (err < 0) {
> x->km.state = XFRM_STATE_DEAD;
> xfrm_dev_state_delete(x);
> - __xfrm_state_put(x);
> + xfrm_state_delete(x);
> goto out;
> }
>
>
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