In the Linux kernel, the following vulnerability has been resolved:
netfilter: nf_conntrack: defer invalid log until after unlock
TCP and SCTP conntrack paths can emit invalid-packet logs while ct->lock is still held.
When invalid logging is routed to nfnetlink_log and conntrack export is enabled, the log path can re-enter conntrack netlink glue and dump the same conntrack again. Protocol attribute dumping may take ct->lock, so logging while holding that lock can deadlock.
Defer the TCP invalid logs by storing only the minimal log context while ct->lock is held and emitting the log after unlocking. Also make the TCP timeout-lowering invalid path return whether a log is needed, then emit that log after unlocking.
Do the same for the SCTP invalid state-transition log that can be reached while ct->lock is held.
Add a lockdep assertion to nf_ct_l4proto_log_invalid() so future callers that log invalid conntracks while holding ct->lock are caught outside TCP and SCTP as well.