In the Linux kernel, the following vulnerability has been resolved:
tty: serial: samsung: Remove redundant port lock acquisition in rx helpers
Sashiko identified a deadlock when the console flow is engaged [1].
When console flow control is enabled (UPF_CONS_FLOW), s3c24xx_serial_stop_tx() calls s3c24xx_serial_rx_enable() and s3c24xx_serial_start_tx() calls s3c24xx_serial_rx_disable().
The serial core framework invokes the .stop_tx() and .start_tx() callbacks with the port->lock spinlock already held. Furthermore, all internal driver paths that invoke stop_tx (such as the DMA TX completion handler s3c24xx_serial_tx_dma_complete() or the PIO TX IRQ handler s3c24xx_serial_tx_irq()) also acquire port->lock prior to calling it. (Note that s3c24xx_serial_start_tx() is only invoked by the serial core).
However, s3c24xx_serial_rx_enable() and s3c24xx_serial_rx_disable() unconditionally attempt to acquire port->lock again using uart_port_lock_irqsave(). Since spinlocks are not recursive, this causes a deadlock on the same CPU when console flow control is engaged.
Remove the redundant lock acquisition from both rx helper functions.
References
- https://git.kernel.org/stable/c/10014eb7eee351f7b587f8ac85830f0c9343cb9a
- https://git.kernel.org/stable/c/14143ec10d69f42806b5d7b046f0fd1b835831ae
- https://git.kernel.org/stable/c/9c92b42207978559e32903c3098aaf5c5b5788b2
- https://git.kernel.org/stable/c/9fd48937046efc9abb89379d63ee9cc5c661d711
- https://git.kernel.org/stable/c/a3bb136bff5e6a5e48cdd813246c9c4686feaaa9
- https://git.kernel.org/stable/c/a9c22e0f93ba18322a6623ecdda2f0cd858ca350
- https://git.kernel.org/stable/c/ee9eb72be95490602c493db050c73d925c3a4d74
- https://git.kernel.org/stable/c/f4c3e63fa8639aedf96fb200d9939945a9eed51e