On Wed, Jul 08, 2020 at 08:08:09AM -0500, Eric W. Biederman wrote: > Luis Chamberlain <mcgrof@xxxxxxxxxx> writes: > > > On Wed, Jul 08, 2020 at 06:35:25AM +0000, Luis Chamberlain wrote: > >> On Thu, Jul 02, 2020 at 11:41:34AM -0500, Eric W. Biederman wrote: > >> > Now that the last callser has been removed remove this code from exec. > >> > > >> > For anyone thinking of resurrecing do_execve_file please note that > >> > the code was buggy in several fundamental ways. > >> > > >> > - It did not ensure the file it was passed was read-only and that > >> > deny_write_access had been called on it. Which subtlely breaks > >> > invaniants in exec. > >> > > >> > - The caller of do_execve_file was expected to hold and put a > >> > reference to the file, but an extra reference for use by exec was > >> > not taken so that when exec put it's reference to the file an > >> > underflow occured on the file reference count. > >> > >> Maybe its my growing love with testing, but I'm going to have to partly > >> blame here that we added a new API without any respective testing. > >> Granted, I recall this this patch set could have used more wider review > >> and a bit more patience... but just mentioning this so we try to avoid > >> new api-without-testing with more reason in the future. > >> > >> But more importantly, *how* could we have caught this? Or how can we > >> catch this sort of stuff better in the future? > > > > Of all the issues you pointed out with do_execve_file(), since upon > > review the assumption *by design* was that LSMs/etc would pick up issues > > with the file *prior* to processing, I think that this file reference > > count issue comes to my attention as the more serious issue which I > > wish we could address *first* before this crusade. > > > > So I have to ask, has anyone *really tried* to give a crack at fixing > > this refcount issue in a smaller way first? Alexei? > > > > I'm not opposed to the removal of do_execve_file(), however if there > > is a reproducible crash / issue with the existing user, this sledge > > hammer seems a bit overkill for older kernels. > > It does not matter for older kernels because there is exactly one user. > That one user is just a place holder keeping the code alive until a real > user comes along. > > For older kernels the solution is to just mark the bpfilter code broken > in Kconfig and refuse to compile it. That is the trivial backportable > fix if anyone wants one. This seals the deal for me, thanks! Carry on, but hey, please add yourself to MAINTAINERS too :) Luis
