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mctp: make __mctp_dev_get() take a refcount hold

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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>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Matt Johnston 2022-02-22 12:17:38 +08:00 committed by David S. Miller
parent 4767b7e2ed
commit dc121c0084
3 changed files with 22 additions and 5 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

21
net/mctp/device.c
View File

@ -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;
}

5
net/mctp/route.c
View File

@ -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 @@ out_release:
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;
}

1
net/mctp/test/utils.c
View File

@ -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;