mctp: make __mctp_dev_get() take a refcount hold
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>
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@ -25,12 +25,25 @@ struct mctp_dump_cb {
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size_t a_idx;
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size_t a_idx;
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};
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};
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/* unlocked: caller must hold rcu_read_lock */
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/* unlocked: caller must hold rcu_read_lock.
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* Returned mctp_dev has its refcount incremented, or NULL if unset.
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*/
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struct mctp_dev *__mctp_dev_get(const struct net_device *dev)
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struct mctp_dev *__mctp_dev_get(const struct net_device *dev)
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{
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{
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return rcu_dereference(dev->mctp_ptr);
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struct mctp_dev *mdev = rcu_dereference(dev->mctp_ptr);
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/* RCU guarantees that any mdev is still live.
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* Zero refcount implies a pending free, return NULL.
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*/
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if (mdev)
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if (!refcount_inc_not_zero(&mdev->refs))
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return NULL;
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return mdev;
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}
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}
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/* Returned mctp_dev does not have refcount incremented. The returned pointer
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* remains live while rtnl_lock is held, as that prevents mctp_unregister()
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*/
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struct mctp_dev *mctp_dev_get_rtnl(const struct net_device *dev)
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struct mctp_dev *mctp_dev_get_rtnl(const struct net_device *dev)
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{
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{
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return rtnl_dereference(dev->mctp_ptr);
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return rtnl_dereference(dev->mctp_ptr);
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@ -124,6 +137,7 @@ static int mctp_dump_addrinfo(struct sk_buff *skb, struct netlink_callback *cb)
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if (mdev) {
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if (mdev) {
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rc = mctp_dump_dev_addrinfo(mdev,
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rc = mctp_dump_dev_addrinfo(mdev,
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skb, cb);
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skb, cb);
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mctp_dev_put(mdev);
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// Error indicates full buffer, this
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// Error indicates full buffer, this
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// callback will get retried.
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// callback will get retried.
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if (rc < 0)
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if (rc < 0)
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@ -298,7 +312,7 @@ void mctp_dev_hold(struct mctp_dev *mdev)
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void mctp_dev_put(struct mctp_dev *mdev)
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void mctp_dev_put(struct mctp_dev *mdev)
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{
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{
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if (refcount_dec_and_test(&mdev->refs)) {
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if (mdev && refcount_dec_and_test(&mdev->refs)) {
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dev_put(mdev->dev);
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dev_put(mdev->dev);
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kfree_rcu(mdev, rcu);
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kfree_rcu(mdev, rcu);
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}
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}
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@ -370,6 +384,7 @@ static size_t mctp_get_link_af_size(const struct net_device *dev,
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if (!mdev)
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if (!mdev)
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return 0;
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return 0;
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ret = nla_total_size(4); /* IFLA_MCTP_NET */
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ret = nla_total_size(4); /* IFLA_MCTP_NET */
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mctp_dev_put(mdev);
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return ret;
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return ret;
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}
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}
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@ -836,7 +836,7 @@ int mctp_local_output(struct sock *sk, struct mctp_route *rt,
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{
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{
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struct mctp_sock *msk = container_of(sk, struct mctp_sock, sk);
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struct mctp_sock *msk = container_of(sk, struct mctp_sock, sk);
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struct mctp_skb_cb *cb = mctp_cb(skb);
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struct mctp_skb_cb *cb = mctp_cb(skb);
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struct mctp_route tmp_rt;
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struct mctp_route tmp_rt = {0};
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struct mctp_sk_key *key;
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struct mctp_sk_key *key;
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struct net_device *dev;
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struct net_device *dev;
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struct mctp_hdr *hdr;
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struct mctp_hdr *hdr;
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@ -948,6 +948,7 @@ out_release:
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mctp_route_release(rt);
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mctp_route_release(rt);
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dev_put(dev);
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dev_put(dev);
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mctp_dev_put(tmp_rt.dev);
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return rc;
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return rc;
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@ -1124,11 +1125,13 @@ static int mctp_pkttype_receive(struct sk_buff *skb, struct net_device *dev,
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rt->output(rt, skb);
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rt->output(rt, skb);
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mctp_route_release(rt);
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mctp_route_release(rt);
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mctp_dev_put(mdev);
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return NET_RX_SUCCESS;
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return NET_RX_SUCCESS;
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err_drop:
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err_drop:
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kfree_skb(skb);
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kfree_skb(skb);
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mctp_dev_put(mdev);
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return NET_RX_DROP;
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return NET_RX_DROP;
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}
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}
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@ -54,7 +54,6 @@ struct mctp_test_dev *mctp_test_create_dev(void)
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rcu_read_lock();
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rcu_read_lock();
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dev->mdev = __mctp_dev_get(ndev);
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dev->mdev = __mctp_dev_get(ndev);
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mctp_dev_hold(dev->mdev);
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rcu_read_unlock();
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rcu_read_unlock();
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return dev;
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return dev;
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