CVE-2024-56655

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.