CVE-2023-52447

Summary

CVE-2023-52447 is a vulnerability affecting the Linux kernel's BPF (Berkeley Packet Filter) subsystem. The issue arises when freeing an inner map in certain conditions, allowing a use-after-free situation. Specifically, the issue occurs when updating or deleting an inner map while it's still being accessed by a non-sleepable or sleepable program. The inner map's ref-counter is decreased directly, leading to its premature freeing by the map_free() function. However, most map_free() callbacks do not use synchronize_rcu() or its variants, causing potential issues for the bpf program that's accessing the inner map. To resolve this issue, the free of inner maps is deferred using call_rcu() or call_rcu_tasks_trace() when releasing the last ref-counter of the BPF map. Additionally, a new rcu_head field is added to the BPF map to reduce size, sharing the same storage space with the work field.

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