CVE-2026-64528 in Linux
Summary
by MITRE • 07/25/2026
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.
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Analysis
by VulDB Data Team • 07/25/2026
The vulnerability identified in the Linux kernel's serial tty subsystem affects the samsung s3c24xx serial driver implementation, specifically targeting a deadlock condition that occurs when console flow control is enabled. This issue manifests within the tty serial framework where the kernel's handling of hardware flow control creates an inconsistent locking pattern that leads to system hangs. The problem was discovered through careful analysis of the driver's interaction with the serial core framework and its handling of console flow control mechanisms, particularly when the UPF_CONS_FLOW flag is active.
The technical flaw stems from improper lock management within the s3c24xx_serial_rx_enable() and s3c24xx_serial_rx_disable() helper functions. These functions perform redundant spinlock acquisitions that conflict with the existing locking mechanism already established by the serial core framework. When console flow control is engaged, the serial core invokes .stop_tx() and .start_tx() callbacks while holding the port->lock spinlock, but these callback handlers subsequently attempt to acquire the same lock again through uart_port_lock_irqsave() calls. This non-recursive spinlock behavior creates a deadlock scenario because the same CPU attempts to acquire a spinlock it already holds, which is explicitly prohibited in Linux kernel locking semantics.
The operational impact of this vulnerability extends beyond simple system hangs to potentially affect entire system availability, particularly in embedded systems relying on serial console functionality. The deadlock occurs specifically when console flow control is enabled, making it critical for systems that depend on serial console output for debugging and system monitoring. This vulnerability affects devices using the samsung s3c24xx serial driver architecture where hardware flow control mechanisms are actively utilized, potentially rendering systems unresponsive during critical operations such as DMA transfer completions or PIO interrupt handling.
This vulnerability aligns with CWE-121, which addresses stack-based buffer overflow conditions, and more specifically relates to CWE-362, concurrent execution using shared resource with improper synchronization. The issue also maps to ATT&CK technique T1489, which involves denying access to systems through various means including creating system hangs or deadlocks. The root cause demonstrates improper lock ordering and recursive locking patterns that violate kernel locking best practices.
Mitigation strategies involve removing the redundant lock acquisition from both s3c24xx_serial_rx_enable() and s3c24xx_serial_rx_disable() functions, eliminating the uart_port_lock_irqsave() calls within these helper functions. This change ensures that the serial driver properly respects the existing locking context established by the serial core framework while maintaining proper synchronization for concurrent access to serial port resources. The fix aligns with standard kernel development practices for spinlock management and prevents potential deadlocks in embedded systems where console flow control is enabled. Additionally, this modification maintains backward compatibility while resolving the specific deadlock condition that occurs during console flow control operations.