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. Luis
