On Mon, May 18, 2026 at 9:35 PM Jakub Kicinski <[email protected]> wrote: > > On Wed, 13 May 2026 14:24:43 -0300 Ricardo Robaina wrote: > > When auditd is bottlenecked (e.g., by slow disk I/O), kauditd blocks on > > the netlink socket. > > Holding socket lock during slow IO sounds very wrong. One could say - > that's abuse of the socket lock? > > > If the wait timeout fully expires (timeo == 0), > > netlink mistakenly interprets the zeroed timeout as a non-blocking > > request. It then triggers netlink_overrun that drops the event, > > completely bypassing the audit subsystem's internal retry queue, and > > falsely returns ENOBUFS to user-space, resulting in the following error: > > > > auditd[]: Error receiving audit netlink packet (No buffer space available) > > > > Fix this by detecting when a blocking sender's timeout has expired > > (timeo == 0 && !nonblock) in netlink_unicast(). In this case, instead > > of retrying with timeo=0 (which would incorrectly trigger netlink_overrun > > on the next iteration), safely free the skb and return -EAGAIN, allowing > > the audit subsystem to gracefully enqueue the pending event into its > > internal backlog. > > The socket _is_ the queue, normally. > > Please explore fixing this in audit? > -- > pw-bot: cr >
Hi Jakub, Thanks for reviewing this patch as well. First, regarding the lock: kauditd does not hold the socket lock during slow I/O. The sleep in netlink_attachskb() uses schedule_timeout() on nlk->wait (a wait queue). No socket lock or mutex is held during the sleep. Second, regarding an audit-only fix: the symptom manifests as sk->sk_err = ENOBUFS set inside netlink_overrun() (called from netlink_attachskb when timeo == 0). Audit has no mechanism to prevent or clear this socket state from the outside. Potential workarounds all fail: (1) Clearing sk_err after the fact is racy and affects other socket ops (2) Avoiding timeouts entirely defeats the anti-deadlock mechanism (3) A new NETLINK_F_RECV_NO_ENOBUFS socket flag doesn't exist in stable kernels where this bug is actively impacting users I've submitted v3 [1] with NETLINK_UNICAST_TIMED as an explicit opt-in constant. This is strictly additive and leaves all existing callers untouched: - Standard blocking (0): unchanged - Standard non-blocking (1, MSG_DONTWAIT): unchanged - Timed blocking (2): new opt-in for audit Would you mind reviewing the v3 and checking if it would be considered? [1] https://lore.kernel.org/audit/[email protected]/T/#u Best regards, Ricardo
