CVE-2025-21809

Summary

CVE-2025-21809 is a vulnerability in the Linux kernel that affects the rxrpc and afs components. The issue arises due to the use of an ordinary spinlock by rxrpc in the context of afs's RCU cleanup, which could result in a deadlock. Specifically, when an rxrpc_peer object runs out of refs, it gets removed from the peer hash table, requiring rxrpc to take a spinlock. However, this spinlock is taken in BH context while the RCU cleanup is ongoing, leading to a potential deadlock. The vulnerability can be mitigated by changing the spinlocks of rxnet->peer_hash_lock back to BH-disabling locks. A lockdep complaint and a stack trace illustrate the inconsistent lock state and the possible deadlock scenario.

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