On Tue, 2022-11-15 at 21:35 -0500, Paul Moore wrote: > On Tue, Nov 15, 2022 at 12:58 PM Roberto Sassu > <roberto.sassu@xxxxxxxxxxxxxxx> wrote: > > From: Roberto Sassu <roberto.sassu@xxxxxxxxxx> > > > > LSMs should not be able to return arbitrary return values, as the callers > > of the LSM infrastructure might not be ready to handle unexpected values > > (e.g. positive values that are first converted to a pointer with ERR_PTR, > > and then evaluated with IS_ERR()). > > > > Modify call_int_hook() to call is_ret_value_allowed(), so that the return > > value from each LSM for a given hook is checked. If for the interval the > > return value falls into the corresponding flag is not set, change the > > return value to the default value, just for the current LSM. > > > > A misbehaving LSM would not have impact on the decision of other LSMs, as > > the loop terminates whenever the return value is not zero. > > > > Signed-off-by: Roberto Sassu <roberto.sassu@xxxxxxxxxx> > > --- > > security/security.c | 34 ++++++++++++++++++++++++++++++++++ > > 1 file changed, 34 insertions(+) > > Casey touched on some of this in his reply to patch 0/4, but basically > I see this as a BPF LSM specific problem and not a generalized LSM > issue that should be addressed at the LSM layer. Especially if the > solution involves incurring additional processing for every LSM hook > instantiation, regardless if a BPF LSM is present. Reading your > overall patchset description I believe that you understand this too. Yes, I had this concern too. Thanks Paul and Casey for taking the time to reply. I liked the fact that the fix is extremely simple, but nevertheless it should not impact the performance, if there are alternative ways. I thought maybe we look at non-zero values, since the check is already there. But it could be that there is an impact for it too (maybe for audit_rule_match?). > If you want to somehow instrument the LSM hook definitions (what I > believe to be the motivation behind patch 3/4) to indicate valid > return values for use by the BPF verifier, I think we could entertain > that, or at least discuss it further, but I'm not inclined to support > any runtime overhead at the LSM layer for a specific LSM. Ok, yes. Patches 1-3 would help to keep in sync the LSM infrastructure and eBPF, but it is not strictly needed. I could propose an eBPF-only alternative to declare sets of functions per interval. More or less, I developed an eBPF-based alternative also for patch 4. It is just a proof of concept. Will propose it, to validate the idea. Thanks Roberto
