[PATCH 5.17 0680/1126] ibmvnic: fix race between xmit and reset

Greg Kroah-Hartman
2022-04-05T09:52:19Z

From: Sukadev Bhattiprolu <sukadev@linux.ibm.com>

[ Upstream commit 4219196d1f662cb10a462eb9e076633a3fc31a15 ]

There is a race between reset and the transmit paths that can lead to
ibmvnic_xmit() accessing an scrq after it has been freed in the reset
path. It can result in a crash like:

Kernel attempted to read user page (0) - exploit attempt? (uid: 0)
BUG: Kernel NULL pointer dereference on read at 0x00000000
Faulting instruction address: 0xc0080000016189f8
Oops: Kernel access of bad area, sig: 11 [#1]
...
NIP [c0080000016189f8] ibmvnic_xmit+0x60/0xb60 [ibmvnic]
LR [c000000000c0046c] dev_hard_start_xmit+0x11c/0x280
Call Trace:
[c008000001618f08] ibmvnic_xmit+0x570/0xb60 [ibmvnic] (unreliable)
[c000000000c0046c] dev_hard_start_xmit+0x11c/0x280
[c000000000c9cfcc] sch_direct_xmit+0xec/0x330
[c000000000bfe640] __dev_xmit_skb+0x3a0/0x9d0
[c000000000c00ad4] __dev_queue_xmit+0x394/0x730
[c008000002db813c] __bond_start_xmit+0x254/0x450 [bonding]
[c008000002db8378] bond_start_xmit+0x40/0xc0 [bonding]
[c000000000c0046c] dev_hard_start_xmit+0x11c/0x280
[c000000000c00ca4] __dev_queue_xmit+0x564/0x730
[c000000000cf97e0] neigh_hh_output+0xd0/0x180
[c000000000cfa69c] ip_finish_output2+0x31c/0x5c0
[c000000000cfd244] __ip_queue_xmit+0x194/0x4f0
[c000000000d2a3c4] __tcp_transmit_skb+0x434/0x9b0
[c000000000d2d1e0] __tcp_retransmit_skb+0x1d0/0x6a0
[c000000000d2d984] tcp_retransmit_skb+0x34/0x130
[c000000000d310e8] tcp_retransmit_timer+0x388/0x6d0
[c000000000d315ec] tcp_write_timer_handler+0x1bc/0x330
[c000000000d317bc] tcp_write_timer+0x5c/0x200
[c000000000243270] call_timer_fn+0x50/0x1c0
[c000000000243704] __run_timers.part.0+0x324/0x460
[c000000000243894] run_timer_softirq+0x54/0xa0
[c000000000ea713c] __do_softirq+0x15c/0x3e0
[c000000000166258] __irq_exit_rcu+0x158/0x190
[c000000000166420] irq_exit+0x20/0x40
[c00000000002853c] timer_interrupt+0x14c/0x2b0
[c000000000009a00] decrementer_common_virt+0x210/0x220
--- interrupt: 900 at plpar_hcall_norets_notrace+0x18/0x2c

The immediate cause of the crash is the access of tx_scrq in the following
snippet during a reset, where the tx_scrq can be either NULL or an address
that will soon be invalid:

ibmvnic_xmit()
{
...
tx_scrq = adapter->tx_scrq[queue_num];
txq = netdev_get_tx_queue(netdev, queue_num);
ind_bufp = &tx_scrq->ind_buf;

if (test_bit(0, &adapter->resetting)) {
...
}

But beyond that, the call to ibmvnic_xmit() itself is not safe during a
reset and the reset path attempts to avoid this by stopping the queue in
ibmvnic_cleanup(). However just after the queue was stopped, an in-flight
ibmvnic_complete_tx() could have restarted the queue even as the reset is
progressing.

Since the queue was restarted we could get a call to ibmvnic_xmit() which
can then access the bad tx_scrq (or other fields).

We cannot however simply have ibmvnic_complete_tx() check the ->resetting
bit and skip starting the queue. This can race at the "back-end" of a good
reset which just restarted the queue but has not cleared the ->resetting
bit yet. If we skip restarting the queue due to ->resetting being true,
the queue would remain stopped indefinitely potentially leading to transmit
timeouts.

IOW ->resetting is too broad for this purpose. Instead use a new flag
that indicates whether or not the queues are active. Only the open/
reset paths control when the queues are active. ibmvnic_complete_tx()
and others wake up the queue only if the queue is marked active.

So we will have:
A. reset/open thread in ibmvnic_cleanup() and __ibmvnic_open()

->resetting = true
->tx_queues_active = false
disable tx queues
...
->tx_queues_active = true
start tx queues

B. Tx interrupt in ibmvnic_complete_tx():

if (->tx_queues_active)
netif_wake_subqueue();

To ensure that ->tx_queues_active and state of the queues are consistent,
we need a lock which:

- must also be taken in the interrupt path (ibmvnic_complete_tx())
- shared across the multiple queues in the adapter (so they don't
become serialized)

Use rcu_read_lock() and have the reset thread synchronize_rcu() after
updating the ->tx_queues_active state.

While here, consolidate a few boolean fields in ibmvnic_adapter for
better alignment.

Based on discussions with Brian King and Dany Madden.

Fixes: 7ed5b31f4a66 ("net/ibmvnic: prevent more than one thread from running in reset")
Reported-by: Vaishnavi Bhat <vaish123@in.ibm.com>
Signed-off-by: Sukadev Bhattiprolu <sukadev@linux.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/net/ethernet/ibm/ibmvnic.c | 63 ++++++++++++++++++++++++------
drivers/net/ethernet/ibm/ibmvnic.h | 7 +++-
2 files changed, 55 insertions(+), 15 deletions(-)

diff --git a/drivers/net/ethernet/ibm/ibmvnic.c b/drivers/net/ethernet/ibm/ibmvnic.c
index b423e94956f1..b4804ce63151 100644
--- a/drivers/net/ethernet/ibm/ibmvnic.c
+++ b/drivers/net/ethernet/ibm/ibmvnic.c
@@ -1429,6 +1429,15 @@ static int __ibmvnic_open(struct net_device *netdev)
return rc;
}

+ adapter->tx_queues_active = true;
+
+ /* Since queues were stopped until now, there shouldn't be any
+ * one in ibmvnic_complete_tx() or ibmvnic_xmit() so maybe we
+ * don't need the synchronize_rcu()? Leaving it for consistency
+ * with setting ->tx_queues_active = false.
+ */
+ synchronize_rcu();
+
netif_tx_start_all_queues(netdev);

if (prev_state == VNIC_CLOSED) {
@@ -1603,6 +1612,14 @@ static void ibmvnic_cleanup(struct net_device *netdev)
struct ibmvnic_adapter *adapter = netdev_priv(netdev);

/* ensure that transmissions are stopped if called by do_reset */
+
+ adapter->tx_queues_active = false;
+
+ /* Ensure complete_tx() and ibmvnic_xmit() see ->tx_queues_active
+ * update so they don't restart a queue after we stop it below.
+ */
+ synchronize_rcu();
+
if (test_bit(0, &adapter->resetting))
netif_tx_disable(netdev);
else
@@ -1842,14 +1859,21 @@ static void ibmvnic_tx_scrq_clean_buffer(struct ibmvnic_adapter *adapter,
tx_buff->skb = NULL;
adapter->netdev->stats.tx_dropped++;
}
+
ind_bufp->index = 0;
+
if (atomic_sub_return(entries, &tx_scrq->used) <=
(adapter->req_tx_entries_per_subcrq / 2) &&
- __netif_subqueue_stopped(adapter->netdev, queue_num) &&
- !test_bit(0, &adapter->resetting)) {
- netif_wake_subqueue(adapter->netdev, queue_num);
- netdev_dbg(adapter->netdev, "Started queue %d\n",
- queue_num);
+ __netif_subqueue_stopped(adapter->netdev, queue_num)) {
+ rcu_read_lock();
+
+ if (adapter->tx_queues_active) {
+ netif_wake_subqueue(adapter->netdev, queue_num);
+ netdev_dbg(adapter->netdev, "Started queue %d\n",
+ queue_num);
+ }
+
+ rcu_read_unlock();
}
}

@@ -1904,11 +1928,12 @@ static netdev_tx_t ibmvnic_xmit(struct sk_buff *skb, struct net_device *netdev)
int index = 0;
u8 proto = 0;

- tx_scrq = adapter->tx_scrq[queue_num];
- txq = netdev_get_tx_queue(netdev, queue_num);
- ind_bufp = &tx_scrq->ind_buf;
-
- if (test_bit(0, &adapter->resetting)) {
+ /* If a reset is in progress, drop the packet since
+ * the scrqs may get torn down. Otherwise use the
+ * rcu to ensure reset waits for us to complete.
+ */
+ rcu_read_lock();
+ if (!adapter->tx_queues_active) {
dev_kfree_skb_any(skb);

tx_send_failed++;
@@ -1917,6 +1942,10 @@ static netdev_tx_t ibmvnic_xmit(struct sk_buff *skb, struct net_device *netdev)
goto out;
}

+ tx_scrq = adapter->tx_scrq[queue_num];
+ txq = netdev_get_tx_queue(netdev, queue_num);
+ ind_bufp = &tx_scrq->ind_buf;
+
if (ibmvnic_xmit_workarounds(skb, netdev)) {
tx_dropped++;
tx_send_failed++;
@@ -1924,6 +1953,7 @@ static netdev_tx_t ibmvnic_xmit(struct sk_buff *skb, struct net_device *netdev)
ibmvnic_tx_scrq_flush(adapter, tx_scrq);
goto out;
}
+
if (skb_is_gso(skb))
tx_pool = &adapter->tso_pool[queue_num];
else
@@ -2078,6 +2108,7 @@ static netdev_tx_t ibmvnic_xmit(struct sk_buff *skb, struct net_device *netdev)
netif_carrier_off(netdev);
}
out:
+ rcu_read_unlock();
netdev->stats.tx_dropped += tx_dropped;
netdev->stats.tx_bytes += tx_bytes;
netdev->stats.tx_packets += tx_packets;
@@ -3732,9 +3763,15 @@ static int ibmvnic_complete_tx(struct ibmvnic_adapter *adapter,
(adapter->req_tx_entries_per_subcrq / 2) &&
__netif_subqueue_stopped(adapter->netdev,
scrq->pool_index)) {
- netif_wake_subqueue(adapter->netdev, scrq->pool_index);
- netdev_dbg(adapter->netdev, "Started queue %d\n",
- scrq->pool_index);
+ rcu_read_lock();
+ if (adapter->tx_queues_active) {
+ netif_wake_subqueue(adapter->netdev,
+ scrq->pool_index);
+ netdev_dbg(adapter->netdev,
+ "Started queue %d\n",
+ scrq->pool_index);
+ }
+ rcu_read_unlock();
}
}

diff --git a/drivers/net/ethernet/ibm/ibmvnic.h b/drivers/net/ethernet/ibm/ibmvnic.h
index fa2d607a7b1b..8f5cefb932dd 100644
--- a/drivers/net/ethernet/ibm/ibmvnic.h
+++ b/drivers/net/ethernet/ibm/ibmvnic.h
@@ -1006,11 +1006,14 @@ struct ibmvnic_adapter {
struct work_struct ibmvnic_reset;
struct delayed_work ibmvnic_delayed_reset;
unsigned long resetting;
- bool napi_enabled, from_passive_init;
- bool login_pending;
/* last device reset time */
unsigned long last_reset_time;

+ bool napi_enabled;
+ bool from_passive_init;
+ bool login_pending;
+ /* protected by rcu */
+ bool tx_queues_active;
bool failover_pending;
bool force_reset_recovery;

--
2.34.1