CVE-2026-23440: net/mlx5e: Fix race condition during IPSec ESN update

In the Linux kernel, the following vulnerability has been resolved:

net/mlx5e: Fix race condition during IPSec ESN update

In IPSec full offload mode, the device reports an ESN (Extended Sequence Number) wrap event to the driver. The driver validates this event by querying the IPSec ASO and checking that the esneventarm field is 0x0, which indicates an event has occurred. After handling the event, the driver must re-arm the context by setting esneventarm back to 0x1.

A race condition exists in this handling path. After validating the event, the driver calls mlx5accelespmodifyxfrm() to update the kernel's xfrm state. This function temporarily releases and re-acquires the xfrm state lock.

So, need to acknowledge the event first by setting esneventarm to 0x1. This prevents the driver from reprocessing the same ESN update if the hardware sends events for other reason. Since the next ESN update only occurs after nearly 2^31 packets are received, there's no risk of missing an update, as it will happen long after this handling has finished.

Processing the event twice causes the ESN high-order bits (esnmsb) to be incremented incorrectly. The driver then programs the hardware with this invalid ESN state, which leads to anti-replay failures and a complete halt of IPSec traffic.

Fix this by re-arming the ESN event immediately after it is validated, before calling mlx5accelespmodifyxfrm(). This ensures that any spurious, duplicate events are correctly ignored, closing the race window.