On Mon, Jun 8, 2020 at 2:04 PM Richard Guy Briggs <rgb@xxxxxxxxxx> wrote: > On 2020-04-22 13:24, Paul Moore wrote: > > On Fri, Apr 17, 2020 at 6:26 PM Eric W. Biederman <ebiederm@xxxxxxxxxxxx> wrote: > > > Paul Moore <paul@xxxxxxxxxxxxxx> writes: > > > > On Thu, Apr 16, 2020 at 4:36 PM Eric W. Biederman <ebiederm@xxxxxxxxxxxx> wrote: > > > >> Paul Moore <paul@xxxxxxxxxxxxxx> writes: > > > >> > On Mon, Mar 30, 2020 at 1:49 PM Richard Guy Briggs <rgb@xxxxxxxxxx> wrote: > > > >> >> On 2020-03-30 13:34, Paul Moore wrote: > > > >> >> > On Mon, Mar 30, 2020 at 12:22 PM Richard Guy Briggs <rgb@xxxxxxxxxx> wrote: > > > >> >> > > On 2020-03-30 10:26, Paul Moore wrote: > > > >> >> > > > On Mon, Mar 30, 2020 at 9:47 AM Richard Guy Briggs <rgb@xxxxxxxxxx> wrote: > > > >> >> > > > > On 2020-03-28 23:11, Paul Moore wrote: > > > >> >> > > > > > On Tue, Mar 24, 2020 at 5:02 PM Richard Guy Briggs <rgb@xxxxxxxxxx> wrote: > > > >> >> > > > > > > On 2020-03-23 20:16, Paul Moore wrote: > > > >> >> > > > > > > > On Thu, Mar 19, 2020 at 6:03 PM Richard Guy Briggs <rgb@xxxxxxxxxx> wrote: > > > >> >> > > > > > > > > On 2020-03-18 18:06, Paul Moore wrote: > > > >> > > > > >> > ... > > > >> > > > > >> >> > > Well, every time a record gets generated, *any* record gets generated, > > > >> >> > > we'll need to check for which audit daemons this record is in scope and > > > >> >> > > generate a different one for each depending on the content and whether > > > >> >> > > or not the content is influenced by the scope. > > > >> >> > > > > >> >> > That's the problem right there - we don't want to have to generate a > > > >> >> > unique record for *each* auditd on *every* record. That is a recipe > > > >> >> > for disaster. > > > >> >> > > > > >> >> > Solving this for all of the known audit records is not something we > > > >> >> > need to worry about in depth at the moment (although giving it some > > > >> >> > casual thought is not a bad thing), but solving this for the audit > > > >> >> > container ID information *is* something we need to worry about right > > > >> >> > now. > > > >> >> > > > >> >> If you think that a different nested contid value string per daemon is > > > >> >> not acceptable, then we are back to issuing a record that has only *one* > > > >> >> contid listed without any nesting information. This brings us back to > > > >> >> the original problem of keeping *all* audit log history since the boot > > > >> >> of the machine to be able to track the nesting of any particular contid. > > > >> > > > > >> > I'm not ruling anything out, except for the "let's just completely > > > >> > regenerate every record for each auditd instance". > > > >> > > > >> Paul I am a bit confused about what you are referring to when you say > > > >> regenerate every record. > > > >> > > > >> Are you saying that you don't want to repeat the sequence: > > > >> audit_log_start(...); > > > >> audit_log_format(...); > > > >> audit_log_end(...); > > > >> for every nested audit daemon? > > > > > > > > If it can be avoided yes. Audit performance is already not-awesome, > > > > this would make it even worse. > > > > > > As far as I can see not repeating sequences like that is fundamental > > > for making this work at all. Just because only the audit subsystem > > > should know about one or multiple audit daemons. Nothing else should > > > care. > > > > Yes, exactly, this has been mentioned in the past. Both the > > performance hit and the code complication in the caller are things we > > must avoid. > > > > > >> Or are you saying that you would like to literraly want to send the same > > > >> skb to each of the nested audit daemons? > > > > > > > > Ideally we would reuse the generated audit messages as much as > > > > possible. Less work is better. That's really my main concern here, > > > > let's make sure we aren't going to totally tank performance when we > > > > have a bunch of nested audit daemons. > > > > > > So I think there are two parts of this answer. Assuming we are talking > > > about nesting audit daemons in containers we will have different > > > rulesets and I expect most of the events for a nested audit daemon won't > > > be of interest to the outer audit daemon. > > > > Yes, this is another thing that Richard and I have discussed in the > > past. We will basically need to create per-daemon queues, rules, > > tracking state, etc.; that is easy enough. What will be slightly more > > tricky is the part where we apply the filters to the individual > > records and decide if that record is valid/desired for a given daemon. > > I think it can be done without too much pain, and any changes to the > > callers, but it will require a bit of work to make sure it is done > > well and that records are needlessly duplicated in the kernel. > > > > > Beyond that it should be very straight forward to keep a pointer and > > > leave the buffer as a scatter gather list until audit_log_end > > > and translate pids, and rewrite ACIDs attributes in audit_log_end > > > when we build the final packet. Either through collaboration with > > > audit_log_format or a special audit_log command that carefully sets > > > up the handful of things that need that information. > > > > In order to maximize record re-use I think we will want to hold off on > > assembling the final packet until it is sent to the daemons in the > > kauditd thread. We'll also likely need to create special > > audit_log_XXX functions to capture fields which we know will need > > translation, e.g. ACID information. (the reason for the new > > audit_log_XXX functions would be to mark the new sg element and ensure > > the buffer is handled correctly) > > > > Regardless of the details, I think the scatter gather approach is the > > key here - that seems like the best design idea I've seen thus far. > > It enables us to replace portions of the record as needed ... and > > possibly use the existing skb cow stuff ... it has been a while, but > > does the skb cow functions handle scatter gather skbs or do they need > > to be linear? > > How does the selection of this data management technique affect our > choice of field format? I'm not sure it affects the record string, but it might affect the in-kernel API as we would likely want to have a special function for logging the audit container ID that does the scatter-gather management for the record. There might also need to be some changes to how we allocate the records. However, since you're the one working on these patches I would expect you to be the one to look into how this would work and what the impacts might be to the code, record format, etc. > Does this lock the field value to a fixed length? I wouldn't think so. In fact if it did it wouldn't really be a good solution. Once again, this is something I would expect you to look into. > Does the use of scatter/gather techniques or structures allow > the use of different lengths of data for each destination (auditd)? This is related to the above ... but yes, the reason why Eric and I were discussing a scatter/gather approach is that it would presumably allow one to break the single record string into pieces which could be managed and manipulated much easier than the monolithic record string. > I could see different target audit daemons triggering or switching to a > different chunk of data and length. This does raise a concern related > to the previous sig_info2 discussion that the struct contobj that exists > at the time of audit_log_exit called could have been reaped by the time > the buffer is pulled from the queue for transmission to auditd, but we > could hold a reference to it as is done for sig_info2. Yes. > Looking through the kernel scatter/gather possibilities, I see struct > iovec which is used by the readv/writev/preadv/pwritev syscalls, but I'm > understanding that this is a kernel implementation that will be not > visible to user space. So would the struct scatterlist be the right > choice? It has been so long since I've looked at the scatter-gather code that I can't really say with any confidence at this point. All I can say is that the scatter-gather code really should just be an implementation detail in the kernel and should not be visible to userspace; userspace should get the same awful, improperly generated netlink message it always has received from the kernel ;) -- paul moore www.paul-moore.com
