On Tue, Mar 16, 2021 at 12:18:33PM -0700, Kees Cook wrote: > On Tue, Mar 16, 2021 at 12:43:12PM +0000, Al Viro wrote: > > On Tue, Mar 16, 2021 at 08:24:50AM +0100, Greg Kroah-Hartman wrote: > > > > > > Completely agreed. seq_get_buf() should be totally ripped out. > > > > Unfortunately, this is going to be a long road because of sysfs's ATTR > > > > stuff, there are something like 5000 callers, and the entire API was > > > > designed to avoid refactoring all those callers from > > > > sysfs_kf_seq_show(). > > > > > > What is wrong with the sysfs ATTR stuff? That should make it so that we > > > do not have to change any caller for any specific change like this, why > > > can't sysfs or kernfs handle it automatically? > > > > Hard to tell, since that would require _finding_ the sodding ->show() > > instances first. Good luck with that, seeing that most of those appear > > to come from templates-done-with-cpp... > > I *think* I can get coccinelle to find them all, but my brute-force > approach was to just do a debug build changing the ATTR macro to be > typed, and changing the name of "show" and "store" in kobj_attribute > (to make the compiler find them all). > > > AFAICS, Kees wants to protect against ->show() instances stomping beyond > > the page size. What I don't get is what do you get from using seq_file > > if you insist on doing raw access to the buffer rather than using > > seq_printf() and friends. What's the point? > > To me, it looks like the kernfs/sysfs API happened around the time > "container_of" was gaining ground. It's trying to do the same thing > the "modern" callbacks do with finding a pointer from another, but it > did so by making sure everything had a 0 offset and an identical > beginning structure layout _but changed prototypes_. > > It's the changed prototypes that freaks out CFI. > > My current plan consists of these steps: > > - add two new callbacks to the kobj_attribute struct (and its clones): > "seq_show" and "seq_store", which will pass in the seq_file. Ick, why? Why should the callback care about seq_file? Shouldn't any wrapper logic in the kobject code be able to handle this automatically? > - convert all callbacks to kobject/kboj_attribute and use container_of() > to find their respective pointers. Which callbacks are you talking about here? > - remove "show" and "store" Hah! > - remove external use of seq_get_buf(). So is this the main goal? I still don't understand the sequence file problem here, what am I missing (becides the CFI stuff that is)? > The first two steps require thousands of lines of code changed, so > I'm going to try to minimize it by trying to do as many conversions as > possible to the appropriate helpers first. e.g. DEVICE_ATTR_INT exists, > but there are only 2 users, yet there appears to be something like 500 > DEVICE_ATTR callers that have an open-coded '%d': > > $ git grep -B10 '\bDEVICE_ATTR' | grep '%d' | wc -l > 530 That's going to be hard, and a pain, and I really doubt all that useful as I still can't figure out why this is needed... thanks, greg k-h
