MPTCP Deadlock Issue in Linux Kernel

CVE-2025-71126

What is CVE-2025-71126?

A vulnerability exists in the Linux Kernel related to multipath TCP (MPTCP), where the absence of appropriate locking mechanisms can lead to a deadlock condition during fallback scenarios. This occurs when an MPTCP connection attempts to acquire a fallback lock while it is already holding that same lock, resulting in potential recursive locking. The issue is compounded when a packet scheduler tries to reinject packets after receiving an MP_FAIL, as it may attempt to do this atomically from the critical fallback section, risking another lock acquisition that could lead to a deadlock. Proper handling of locks during these operations is crucial to prevent such scenarios.

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