On Tue, May 26, 2026 at 5:54 PM Paul Moore <[email protected]> wrote: > > On Mon, May 18, 2026 at 8:35 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? > > It's no different than any other kernel subsystem sending netlink > packets to userspace, although in some configurations the rate at > which audit sends netlink traffic is likely much higher than the > majority of netlink users. > > Arguably, audit probably never should have used netlink, but that > decision happened a long time ago and there were other issues > complicating the decision. > > > > 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. > > There is a joke in there about audit and "normal", but I'll leave that > as an exercise for the reader. I will say that audit has a lot of > unique requirements regarding queue management and that dictates a lot > of the wacky stuff audit has to do with it's record queue; the > standard socket buffer functionality doesn't have everything, and I > wouldn't want to ask for it to be augmented in a way that satisfies > audit. > > > Please explore fixing this in audit? > > Ricardo, I was kinda hoping not to have to do this in audit, but I > think you can probably get away with just open-coding > netlink_unicast() in audit and then going from there ... we might want > to do some other things differently, but let's see what a basic patch > looks like before we spend a lot time redesigning it. > > -- > paul-moore.com >
Hi Paul, Thank you for your input here, I appreciate it. Before pursuing the open-coding approach, I wanted to let you know I have a v3 patch [1] ready that addresses the concerns raised before. It introduces NETLINK_UNICAST_TIMED as an explicit opt-in constant (value 2) rather than the broader heuristic in v2. Would you be open to reviewing this approach first? If you still prefer the open-coding route or if v3 gets pushed back, I'm happy to go that direction. [1] https://lore.kernel.org/audit/[email protected]/T/#u Best regards, Ricardo
