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.
