From: Matt Johnston matt@codeconstruct.com.au
[ Upstream commit dc121c0084910db985cf1c8ba6fce5d8c307cc02 ]
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 Signed-off-by: Sasha Levin sashal@kernel.org --- 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 ef2755f82f87..f86ef6d751bd 100644 --- a/net/mctp/device.c +++ b/net/mctp/device.c @@ -24,12 +24,25 @@ 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); @@ -123,6 +136,7 @@ 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) @@ -297,7 +311,7 @@ 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); } @@ -369,6 +383,7 @@ 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 e52cef750500..05fbd318eb98 100644 --- a/net/mctp/route.c +++ b/net/mctp/route.c @@ -786,7 +786,7 @@ 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; @@ -892,6 +892,7 @@ 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;
@@ -1057,11 +1058,13 @@ 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;