On 12/9/2023 10:08 AM, Paul Moore wrote: > On Fri, Dec 8, 2023 at 7:24 PM Casey Schaufler <casey@xxxxxxxxxxxxxxxx> wrote: >> On 12/8/2023 3:32 PM, Paul Moore wrote: >>> On Fri, Dec 8, 2023 at 6:21 PM Casey Schaufler <casey@xxxxxxxxxxxxxxxx> wrote: >>>> On 12/8/2023 2:43 PM, Paul Moore wrote: >>>>> On Thu, Dec 7, 2023 at 9:14 PM Munehisa Kamata <kamatam@xxxxxxxxxx> wrote: >>>>>> On Tue, 2023-12-05 14:21:51 -0800, Paul Moore wrote: >>>>> .. >>>>> >>>>>>> I think my thoughts are neatly summarized by Andrew's "yuk!" comment >>>>>>> at the top. However, before we go too much further on this, can we >>>>>>> get clarification that Casey was able to reproduce this on a stock >>>>>>> upstream kernel? Last I read in the other thread Casey wasn't seeing >>>>>>> this problem on Linux v6.5. >>>>>>> >>>>>>> However, for the moment I'm going to assume this is a real problem, is >>>>>>> there some reason why the existing pid_revalidate() code is not being >>>>>>> called in the bind mount case? From what I can see in the original >>>>>>> problem report, the path walk seems to work okay when the file is >>>>>>> accessed directly from /proc, but fails when done on the bind mount. >>>>>>> Is there some problem with revalidating dentrys on bind mounts? >>>>>> Hi Paul, >>>>>> >>>>>> https://lkml.kernel.org/linux-fsdevel/20090608201745.GO8633@xxxxxxxxxxxxxxxxxx/ >>>>>> >>>>>> After reading this thread, I have doubt about solving this in VFS. >>>>>> Honestly, however, I'm not sure if it's entirely relevant today. >>>>> Have you tried simply mounting proc a second time instead of using a bind mount? >>>>> >>>>> % mount -t proc non /new/location/for/proc >>>>> >>>>> I ask because from your description it appears that proc does the >>>>> right thing with respect to revalidation, it only becomes an issue >>>>> when accessing proc through a bind mount. Or did I misunderstand the >>>>> problem? >>>> It's not hard to make the problem go away by performing some simple >>>> action. I was unable to reproduce the problem initially because I >>>> checked the Smack label on the bind mounted proc entry before doing >>>> the cat of it. The problem shows up if nothing happens to update the >>>> inode. >>> A good point. >>> >>> I'm kinda thinking we just leave things as-is, especially since the >>> proposed fix isn't something anyone is really excited about. >> "We have to compromise the performance of our sandboxing tool because of >> a kernel bug that's known and for which a fix is available." >> >> If this were just a curiosity that wasn't affecting real development I >> might agree. But we've got a real world problem, and I don't see ignoring >> it as a good approach. I can't see maintainers of other LSMs thinking so >> if this were interfering with their users. > While the reproducer may be written for Smack, there are plenty of > indications that this applies to all LSMs and my comments have taken > that into account. > > If you're really that upset, try channeling that outrage into your > editor and draft a patch for this that isn't awful. We could "just" wait for the lsm_set_self_attr() syscall to land, and suggest that it be used instead of the buggy /proc interfaces. I would love to propose a patch that's less sucky, but have not come up with one. My understanding of VFS internals isn't up to the task, I fear.
