* [PATCH net-next v3 1/2] mctp: make __mctp_dev_get() take a refcount hold
2022-02-22 4:17 [PATCH net-next v3 0/2] mctp: Fix incorrect refs for extended addr Matt Johnston
@ 2022-02-22 4:17 ` Matt Johnston
2022-02-23 3:59 ` Jakub Kicinski
2022-02-22 4:17 ` [PATCH net-next v3 2/2] mctp: Fix incorrect netdev unref for extended addr Matt Johnston
2022-02-23 12:30 ` [PATCH net-next v3 0/2] mctp: Fix incorrect refs " patchwork-bot+netdevbpf
2 siblings, 1 reply; 6+ messages in thread
From: Matt Johnston @ 2022-02-22 4:17 UTC (permalink / raw)
To: netdev; +Cc: David S. Miller, Jakub Kicinski, Jeremy Kerr
Previously there was a race that could allow the mctp_dev refcount
to hit zero:
rcu_read_lock();
mdev = __mctp_dev_get(dev);
// mctp_unregister() happens here, mdev->refs hits zero
mctp_dev_hold(dev);
rcu_read_unlock();
Now we make __mctp_dev_get() take the hold itself. It is safe to test
against the zero refcount because __mctp_dev_get() is called holding
rcu_read_lock and mctp_dev uses kfree_rcu().
Reported-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Matt Johnston <matt@codeconstruct.com.au>
---
net/mctp/device.c | 21 ++++++++++++++++++---
net/mctp/route.c | 5 ++++-
net/mctp/test/utils.c | 1 -
3 files changed, 22 insertions(+), 5 deletions(-)
diff --git a/net/mctp/device.c b/net/mctp/device.c
index 9e097e61f23a..b754c31162b1 100644
--- a/net/mctp/device.c
+++ b/net/mctp/device.c
@@ -25,12 +25,25 @@ struct mctp_dump_cb {
size_t a_idx;
};
-/* unlocked: caller must hold rcu_read_lock */
+/* unlocked: caller must hold rcu_read_lock.
+ * Returned mctp_dev has its refcount incremented, or NULL if unset.
+ */
struct mctp_dev *__mctp_dev_get(const struct net_device *dev)
{
- return rcu_dereference(dev->mctp_ptr);
+ struct mctp_dev *mdev = rcu_dereference(dev->mctp_ptr);
+
+ /* RCU guarantees that any mdev is still live.
+ * Zero refcount implies a pending free, return NULL.
+ */
+ if (mdev)
+ if (!refcount_inc_not_zero(&mdev->refs))
+ return NULL;
+ return mdev;
}
+/* Returned mctp_dev does not have refcount incremented. The returned pointer
+ * remains live while rtnl_lock is held, as that prevents mctp_unregister()
+ */
struct mctp_dev *mctp_dev_get_rtnl(const struct net_device *dev)
{
return rtnl_dereference(dev->mctp_ptr);
@@ -124,6 +137,7 @@ static int mctp_dump_addrinfo(struct sk_buff *skb, struct netlink_callback *cb)
if (mdev) {
rc = mctp_dump_dev_addrinfo(mdev,
skb, cb);
+ mctp_dev_put(mdev);
// Error indicates full buffer, this
// callback will get retried.
if (rc < 0)
@@ -298,7 +312,7 @@ void mctp_dev_hold(struct mctp_dev *mdev)
void mctp_dev_put(struct mctp_dev *mdev)
{
- if (refcount_dec_and_test(&mdev->refs)) {
+ if (mdev && refcount_dec_and_test(&mdev->refs)) {
dev_put(mdev->dev);
kfree_rcu(mdev, rcu);
}
@@ -370,6 +384,7 @@ static size_t mctp_get_link_af_size(const struct net_device *dev,
if (!mdev)
return 0;
ret = nla_total_size(4); /* IFLA_MCTP_NET */
+ mctp_dev_put(mdev);
return ret;
}
diff --git a/net/mctp/route.c b/net/mctp/route.c
index fe6c8bf1ec2c..6f277e56b168 100644
--- a/net/mctp/route.c
+++ b/net/mctp/route.c
@@ -836,7 +836,7 @@ int mctp_local_output(struct sock *sk, struct mctp_route *rt,
{
struct mctp_sock *msk = container_of(sk, struct mctp_sock, sk);
struct mctp_skb_cb *cb = mctp_cb(skb);
- struct mctp_route tmp_rt;
+ struct mctp_route tmp_rt = {0};
struct mctp_sk_key *key;
struct net_device *dev;
struct mctp_hdr *hdr;
@@ -948,6 +948,7 @@ int mctp_local_output(struct sock *sk, struct mctp_route *rt,
mctp_route_release(rt);
dev_put(dev);
+ mctp_dev_put(tmp_rt.dev);
return rc;
@@ -1124,11 +1125,13 @@ static int mctp_pkttype_receive(struct sk_buff *skb, struct net_device *dev,
rt->output(rt, skb);
mctp_route_release(rt);
+ mctp_dev_put(mdev);
return NET_RX_SUCCESS;
err_drop:
kfree_skb(skb);
+ mctp_dev_put(mdev);
return NET_RX_DROP;
}
diff --git a/net/mctp/test/utils.c b/net/mctp/test/utils.c
index 7b7918702592..e03ba66bbe18 100644
--- a/net/mctp/test/utils.c
+++ b/net/mctp/test/utils.c
@@ -54,7 +54,6 @@ struct mctp_test_dev *mctp_test_create_dev(void)
rcu_read_lock();
dev->mdev = __mctp_dev_get(ndev);
- mctp_dev_hold(dev->mdev);
rcu_read_unlock();
return dev;
--
2.32.0
^ permalink raw reply related [flat|nested] 6+ messages in thread* [PATCH net-next v3 2/2] mctp: Fix incorrect netdev unref for extended addr
2022-02-22 4:17 [PATCH net-next v3 0/2] mctp: Fix incorrect refs for extended addr Matt Johnston
2022-02-22 4:17 ` [PATCH net-next v3 1/2] mctp: make __mctp_dev_get() take a refcount hold Matt Johnston
@ 2022-02-22 4:17 ` Matt Johnston
2022-02-23 12:30 ` [PATCH net-next v3 0/2] mctp: Fix incorrect refs " patchwork-bot+netdevbpf
2 siblings, 0 replies; 6+ messages in thread
From: Matt Johnston @ 2022-02-22 4:17 UTC (permalink / raw)
To: netdev; +Cc: David S. Miller, Jakub Kicinski, Jeremy Kerr
In the extended addressing local route output codepath
dev_get_by_index_rcu() doesn't take a dev_hold() so we shouldn't
dev_put().
Signed-off-by: Matt Johnston <matt@codeconstruct.com.au>
---
net/mctp/route.c | 8 ++------
1 file changed, 2 insertions(+), 6 deletions(-)
diff --git a/net/mctp/route.c b/net/mctp/route.c
index 6f277e56b168..5078ce3315cf 100644
--- a/net/mctp/route.c
+++ b/net/mctp/route.c
@@ -838,7 +838,6 @@ int mctp_local_output(struct sock *sk, struct mctp_route *rt,
struct mctp_skb_cb *cb = mctp_cb(skb);
struct mctp_route tmp_rt = {0};
struct mctp_sk_key *key;
- struct net_device *dev;
struct mctp_hdr *hdr;
unsigned long flags;
unsigned int mtu;
@@ -851,12 +850,12 @@ int mctp_local_output(struct sock *sk, struct mctp_route *rt,
if (rt) {
ext_rt = false;
- dev = NULL;
-
if (WARN_ON(!rt->dev))
goto out_release;
} else if (cb->ifindex) {
+ struct net_device *dev;
+
ext_rt = true;
rt = &tmp_rt;
@@ -866,7 +865,6 @@ int mctp_local_output(struct sock *sk, struct mctp_route *rt,
rcu_read_unlock();
return rc;
}
-
rt->dev = __mctp_dev_get(dev);
rcu_read_unlock();
@@ -947,11 +945,9 @@ int mctp_local_output(struct sock *sk, struct mctp_route *rt,
if (!ext_rt)
mctp_route_release(rt);
- dev_put(dev);
mctp_dev_put(tmp_rt.dev);
return rc;
-
}
/* route management */
--
2.32.0
^ permalink raw reply related [flat|nested] 6+ messages in thread