Advisory [CVE-2026-64459] restore RCU grace period in tcp_ao_destroy_sock
This security Red Hat Linux advisory covers CVE-2026-64459.
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Summary
In the Linux kernel, the following vulnerability has been resolved: tcp: restore RCU grace period in tcp_ao_destroy_sock Commit 51e547e8c89c ("tcp: Free TCP-AO/TCP-MD5 info/keys without RCU") removed the call_rcu() callback from tcp_ao_destroy_sock(), arguing that "the destruction of info/keys is delayed until the socket destructor" and therefore "no one can discover it anymore".
That argument does not hold for the call site in tcp_connect() (net/ipv4/tcp_output.c:4327-4332).
At that point the socket is in TCP_SYN_SENT, has already been inserted into the inet ehash by inet_hash_connect() in tcp_v4_connect(), and is therefore very much discoverable: any softirq running tcp_v4_rcv() on another CPU can take the socket out of the ehash, walk into tcp_inbound_hash(), and load tp->ao_info via implicit RCU before bh_lock_sock_nested() is taken on the destroying CPU.
The reader path then enters __tcp_ao_do_lookup() (net/ipv4/tcp_ao.c:208) which re-loads tp->ao_info via rcu_dereference_check(); the re-load can still observe the (about-to-be-freed) pointer because there is no synchronize_rcu() between rcu_assign_pointer(tp->ao_info, NULL) and tcp_ao_info_free() in tcp_ao_destroy_sock().
Affected versions
No affected-version range was extracted from the source record. The vendor advisory is authoritative — check it before change work.
Official advisory · medium-confidence parse· fetched 13 days ago·verify at source
Fixed versions
No fixed release is recorded yet. That does not prove no patch exists — confirm against the vendor advisory.
Official advisory · medium-confidence parse· fetched 13 days ago·verify at source
Mitigation
The source record does not include mitigation steps. That is not a statement that no fix exists — read the vendor advisory below for the authoritative guidance.
Official advisory · medium-confidence parse· fetched 13 days ago·verify at source
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