[PATCH AUTOSEL 4.19 34/57] xfrm: destroy xfrm_state synchronously on net exit path

Sasha Levin
2019-03-30T01:39:12Z

From: Cong Wang <xiyou.wangcong@gmail.com>

[ Upstream commit f75a2804da391571563c4b6b29e7797787332673 ]

xfrm_state_put() moves struct xfrm_state to the GC list
and schedules the GC work to clean it up. On net exit call
path, xfrm_state_flush() is called to clean up and
xfrm_flush_gc() is called to wait for the GC work to complete
before exit.

However, this doesn't work because one of the ->destructor(),
ipcomp_destroy(), schedules the same GC work again inside
the GC work. It is hard to wait for such a nested async
callback. This is also why syzbot still reports the following
warning:

WARNING: CPU: 1 PID: 33 at net/ipv6/xfrm6_tunnel.c:351 xfrm6_tunnel_net_exit+0x2cb/0x500 net/ipv6/xfrm6_tunnel.c:351
...
ops_exit_list.isra.0+0xb0/0x160 net/core/net_namespace.c:153
cleanup_net+0x51d/0xb10 net/core/net_namespace.c:551
process_one_work+0xd0c/0x1ce0 kernel/workqueue.c:2153
worker_thread+0x143/0x14a0 kernel/workqueue.c:2296
kthread+0x357/0x430 kernel/kthread.c:246
ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:352

In fact, it is perfectly fine to bypass GC and destroy xfrm_state
synchronously on net exit call path, because it is in process context
and doesn't need a work struct to do any blocking work.

This patch introduces xfrm_state_put_sync() which simply bypasses
GC, and lets its callers to decide whether to use this synchronous
version. On net exit path, xfrm_state_fini() and
xfrm6_tunnel_net_exit() use it. And, as ipcomp_destroy() itself is
blocking, it can use xfrm_state_put_sync() directly too.

Also rename xfrm_state_gc_destroy() to ___xfrm_state_destroy() to
reflect this change.

Fixes: b48c05ab5d32 ("xfrm: Fix warning in xfrm6_tunnel_net_exit.")
Reported-and-tested-by: syzbot+e9aebef558e3ed673934@syzkaller.appspotmail.com
Cc: Steffen Klassert <steffen.klassert@secunet.com>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
include/net/xfrm.h | 12 +++++++++---
net/ipv6/xfrm6_tunnel.c | 2 +-
net/key/af_key.c | 2 +-
net/xfrm/xfrm_state.c | 30 +++++++++++++++++++-----------
net/xfrm/xfrm_user.c | 2 +-
5 files changed, 31 insertions(+), 17 deletions(-)

diff --git a/include/net/xfrm.h b/include/net/xfrm.h
index da588def3c61..5e3daf53b3d1 100644
--- a/include/net/xfrm.h
+++ b/include/net/xfrm.h
@@ -850,7 +850,7 @@ static inline void xfrm_pols_put(struct xfrm_policy **pols, int npols)
xfrm_pol_put(pols[i]);
}

-void __xfrm_state_destroy(struct xfrm_state *);
+void __xfrm_state_destroy(struct xfrm_state *, bool);

static inline void __xfrm_state_put(struct xfrm_state *x)
{
@@ -860,7 +860,13 @@ static inline void __xfrm_state_put(struct xfrm_state *x)
static inline void xfrm_state_put(struct xfrm_state *x)
{
if (refcount_dec_and_test(&x->refcnt))
- __xfrm_state_destroy(x);
+ __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)
@@ -1616,7 +1622,7 @@ struct xfrmk_spdinfo {

struct xfrm_state *xfrm_find_acq_byseq(struct net *net, u32 mark, u32 seq);
int xfrm_state_delete(struct xfrm_state *x);
-int xfrm_state_flush(struct net *net, u8 proto, bool task_valid);
+int xfrm_state_flush(struct net *net, u8 proto, bool task_valid, bool sync);
int xfrm_dev_state_flush(struct net *net, struct net_device *dev, bool task_valid);
void xfrm_sad_getinfo(struct net *net, struct xfrmk_sadinfo *si);
void xfrm_spd_getinfo(struct net *net, struct xfrmk_spdinfo *si);
diff --git a/net/ipv6/xfrm6_tunnel.c b/net/ipv6/xfrm6_tunnel.c
index f5b4febeaa25..bc65db782bfb 100644
--- a/net/ipv6/xfrm6_tunnel.c
+++ b/net/ipv6/xfrm6_tunnel.c
@@ -344,8 +344,8 @@ static void __net_exit xfrm6_tunnel_net_exit(struct net *net)
struct xfrm6_tunnel_net *xfrm6_tn = xfrm6_tunnel_pernet(net);
unsigned int i;

- xfrm_state_flush(net, IPSEC_PROTO_ANY, false);
xfrm_flush_gc();
+ xfrm_state_flush(net, IPSEC_PROTO_ANY, false, true);

for (i = 0; i < XFRM6_TUNNEL_SPI_BYADDR_HSIZE; i++)
WARN_ON_ONCE(!hlist_empty(&xfrm6_tn->spi_byaddr[i]));
diff --git a/net/key/af_key.c b/net/key/af_key.c
index 7da629d59717..7d4bed955060 100644
--- a/net/key/af_key.c
+++ b/net/key/af_key.c
@@ -1773,7 +1773,7 @@ static int pfkey_flush(struct sock *sk, struct sk_buff *skb, const struct sadb_m
if (proto == 0)
return -EINVAL;

- err = xfrm_state_flush(net, proto, true);
+ err = xfrm_state_flush(net, proto, true, false);
err2 = unicast_flush_resp(sk, hdr);
if (err || err2) {
if (err == -ESRCH) /* empty table - go quietly */
diff --git a/net/xfrm/xfrm_state.c b/net/xfrm/xfrm_state.c
index cc0203efb584..3f729cd512af 100644
--- a/net/xfrm/xfrm_state.c
+++ b/net/xfrm/xfrm_state.c
@@ -432,7 +432,7 @@ void xfrm_state_free(struct xfrm_state *x)
}
EXPORT_SYMBOL(xfrm_state_free);

-static void xfrm_state_gc_destroy(struct xfrm_state *x)
+static void ___xfrm_state_destroy(struct xfrm_state *x)
{
tasklet_hrtimer_cancel(&x->mtimer);
del_timer_sync(&x->rtimer);
@@ -474,7 +474,7 @@ static void xfrm_state_gc_task(struct work_struct *work)
synchronize_rcu();

hlist_for_each_entry_safe(x, tmp, &gc_list, gclist)
- xfrm_state_gc_destroy(x);
+ ___xfrm_state_destroy(x);
}

static enum hrtimer_restart xfrm_timer_handler(struct hrtimer *me)
@@ -598,14 +598,19 @@ struct xfrm_state *xfrm_state_alloc(struct net *net)
}
EXPORT_SYMBOL(xfrm_state_alloc);

-void __xfrm_state_destroy(struct xfrm_state *x)
+void __xfrm_state_destroy(struct xfrm_state *x, bool sync)
{
WARN_ON(x->km.state != XFRM_STATE_DEAD);

- 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);
+ 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);

@@ -708,7 +713,7 @@ xfrm_dev_state_flush_secctx_check(struct net *net, struct net_device *dev, bool
}
#endif

-int xfrm_state_flush(struct net *net, u8 proto, bool task_valid)
+int xfrm_state_flush(struct net *net, u8 proto, bool task_valid, bool sync)
{
int i, err = 0, cnt = 0;

@@ -730,7 +735,10 @@ int xfrm_state_flush(struct net *net, u8 proto, bool task_valid)
err = xfrm_state_delete(x);
xfrm_audit_state_delete(x, err ? 0 : 1,
task_valid);
- xfrm_state_put(x);
+ if (sync)
+ xfrm_state_put_sync(x);
+ else
+ xfrm_state_put(x);
if (!err)
cnt++;

@@ -2217,7 +2225,7 @@ 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(t);
+ xfrm_state_put_sync(t);
x->tunnel = NULL;
}
}
@@ -2377,8 +2385,8 @@ void xfrm_state_fini(struct net *net)
unsigned int sz;

flush_work(&net->xfrm.state_hash_work);
- xfrm_state_flush(net, IPSEC_PROTO_ANY, false);
flush_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 ab557827aac0..7e4904b93004 100644
--- a/net/xfrm/xfrm_user.c
+++ b/net/xfrm/xfrm_user.c
@@ -1932,7 +1932,7 @@ static int xfrm_flush_sa(struct sk_buff *skb, struct nlmsghdr *nlh,
struct xfrm_usersa_flush *p = nlmsg_data(nlh);
int err;

- err = xfrm_state_flush(net, p->proto, true);
+ err = xfrm_state_flush(net, p->proto, true, false);
if (err) {
if (err == -ESRCH) /* empty table */
return 0;
--
2.19.1