Affected: Linux

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

net: ks8851: Reinstate disabling of BHs around IRQ handler

If the driver executes ks8851_irq() AND a TX packet has been sent, then the driver enables TX queue via netif_wake_queue() which schedules TX softirq to queue packets for this device.

If CONFIG_PREEMPT_RT=y is set AND a packet has also been received by the MAC, then ks8851_rx_pkts() calls netdev_alloc_skb_ip_align() to allocate SKBs for the received packets. If netdev_alloc_skb_ip_align() is called with BH enabled, then local_bh_enable() at the end of netdev_alloc_skb_ip_align() will trigger the pending softirq processing, which may ultimately call the .xmit callback ks8851_start_xmit_par(). The ks8851_start_xmit_par() will try to lock struct ks8851_net_par .lock spinlock, which is already locked by ks8851_irq() from which ks8851_start_xmit_par() was called. This leads to a deadlock, which is reported by the kernel, including a trace listed below.

If CONFIG_PREEMPT_RT is not set, then since commit 0913ec336a6c0 ("net: ks8851: Fix deadlock with the SPI chip variant") the deadlock can also be triggered without received packet in the RX FIFO. The pending softirqs will be processed on return from spin_unlock_bh(&ks->statelock) in ks8851_irq(), which triggers the deadlock as well.

Fix the problem by disabling BH around critical sections, including the IRQ handler, thus preventing the net_tx_action() softirq from triggering during these critical secti…