On Thu, Dec 7, 2023 at 9:14 PM Munehisa Kamata [off-list ref] wrote:

On Tue, 2023-12-05 14:21:51 -0800, Paul Moore wrote:

...

quoted

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@ZenIV.linux.org.uk/

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?

--
paul-moore.com