CVE-2025-71132

A locking context bug was found in the Linux kernel's smc91x Ethernet driver on PREEMPT_RT kernels. The smc_special_trylock() function disables IRQs but smc_special_unlock() does not properly restore IRQs on PREEMPT_RT. This mismatch causes RCU read unlock to fail in __dev_queue_xmit(), triggering a "workqueue leaked atomic, lock or RCU" warning.

This vulnerability specifically affects PREEMPT_RT kernel configurations with smc91x network hardware, typically found in embedded ARM systems and emulated environments like ARM FVP. Standard kernel builds are not affected. The issue causes kernel warnings and potential network subsystem instability but is limited to specialized real-time configurations.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.

To mitigate this issue, prevent the smc91x module from being loaded if this legacy Ethernet hardware is not required. See https://access.redhat.com/solutions/41278 for instructions on how to blacklist a kernel module.