CVE-2024-56655

Summary

In the Linux kernel, the following vulnerability has been resolved:

netfilter: nf_tables: do not defer rule destruction via call_rcu

nf_tables_chain_destroy can sleep, it can't be used from call_rcu callbacks.

Moreover, nf_tables_rule_release() is only safe for error unwinding, while transaction mutex is held and the to-be-desroyed rule was not exposed to either dataplane or dumps, as it deactives+frees without the required synchronize_rcu() in-between.

nft_rule_expr_deactivate() callbacks will change ->use counters of other chains/sets, see e.g. nft_lookup .deactivate callback, these must be serialized via transaction mutex.

Also add a few lockdep asserts to make this more explicit.

Calling synchronize_rcu() isn't ideal, but fixing this without is hard and way more intrusive. As-is, we can get:

WARNING: .. net/netfilter/nf_tables_api.c:5515 nft_set_destroy+0x.. Workqueue: events nf_tables_trans_destroy_work RIP: 0010:nft_set_destroy+0x3fe/0x5c0 Call Trace: <TASK> nf_tables_trans_destroy_work+0x6b7/0xad0 process_one_work+0x64a/0xce0 worker_thread+0x613/0x10d0

In case the synchronize_rcu becomes an issue, we can explore alternatives.

One way would be to allocate nft_trans_rule objects + one nft_trans_chain object, deactivate the rules + the chain and then defer the freeing to the nft destroy workqueue. We'd still need to keep the synchronize_rcu path as a fallback to handle -ENOMEM corner cases though.

Affected Software

Weaknesses

References

• https://git.kernel.org/stable/c/5146c27b2780aac59876a887a5f4e793b8949862
• https://git.kernel.org/stable/c/2991dc357a28b61c13ed1f7b59e9251e2b4562fb
• https://git.kernel.org/stable/c/b8d8f53e1858178882b881b8c09f94ef0e83bf76
• https://git.kernel.org/stable/c/b0f013bebf94fe7ae75e5a53be2f2bd1cc1841e3
• https://git.kernel.org/stable/c/27f0574253f6c24c8ee4e3f0a685b75ed3a256ed
• https://git.kernel.org/stable/c/7cf0bd232b565d9852cb25fd094f77254773e048
• https://git.kernel.org/stable/c/b04df3da1b5c6f6dc7cdccc37941740c078c4043

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