[PATCH 5.18 060/158] net/tls: Fix race in TLS device down flow

Greg Kroah-Hartman
2022-07-27T17:36:12Z

From: Tariq Toukan <tariqt@nvidia.com>

[ Upstream commit f08d8c1bb97c48f24a82afaa2fd8c140f8d3da8b ]

Socket destruction flow and tls_device_down function sync against each
other using tls_device_lock and the context refcount, to guarantee the
device resources are freed via tls_dev_del() by the end of
tls_device_down.

In the following unfortunate flow, this won't happen:
- refcount is decreased to zero in tls_device_sk_destruct.
- tls_device_down starts, skips the context as refcount is zero, going
all the way until it flushes the gc work, and returns without freeing
the device resources.
- only then, tls_device_queue_ctx_destruction is called, queues the gc
work and frees the context's device resources.

Solve it by decreasing the refcount in the socket's destruction flow
under the tls_device_lock, for perfect synchronization. This does not
slow down the common likely destructor flow, in which both the refcount
is decreased and the spinlock is acquired, anyway.

Fixes: e8f69799810c ("net/tls: Add generic NIC offload infrastructure")
Reviewed-by: Maxim Mikityanskiy <maximmi@nvidia.com>
Signed-off-by: Tariq Toukan <tariqt@nvidia.com>
Reviewed-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/tls/tls_device.c | 8 +++++---
1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/net/tls/tls_device.c b/net/tls/tls_device.c
index 3a61bb594544..9c3933781ad4 100644
--- a/net/tls/tls_device.c
+++ b/net/tls/tls_device.c
@@ -97,13 +97,16 @@ static void tls_device_queue_ctx_destruction(struct tls_context *ctx)
unsigned long flags;

spin_lock_irqsave(&tls_device_lock, flags);
+ if (unlikely(!refcount_dec_and_test(&ctx->refcount)))
+ goto unlock;
+
list_move_tail(&ctx->list, &tls_device_gc_list);

/* schedule_work inside the spinlock
* to make sure tls_device_down waits for that work.
*/
schedule_work(&tls_device_gc_work);
-
+unlock:
spin_unlock_irqrestore(&tls_device_lock, flags);
}

@@ -194,8 +197,7 @@ void tls_device_sk_destruct(struct sock *sk)
clean_acked_data_disable(inet_csk(sk));
}

- if (refcount_dec_and_test(&tls_ctx->refcount))
- tls_device_queue_ctx_destruction(tls_ctx);
+ tls_device_queue_ctx_destruction(tls_ctx);
}
EXPORT_SYMBOL_GPL(tls_device_sk_destruct);

--
2.35.1