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    SubjectRe: [PATCH 0/2] vfs: ensure that dentries are revalidated on open (try #2)
    Hi!

    > > > This is the second attempt to fix this problem. The first one attempted
    > > > to fix this in procfs, but Eric Biederman pointed out that file bind
    > > > mounts have a similar problem. This set attempts to fix the issue at a
    > > > higher level, in the generic VFS layer.
    > > >
    > > > In certain situations, when it knows that they are valid, the path
    > > > walking code will skip revalidating dentries that it finds in the cache.
    > > > This causes problems with filesystems such as NFSv4 and CIFS that depend
    > > > on the d_revalidate routine to do opens during lookup.
    > >
    > > ...and it allows bypassing directory permissions. Could we fix both
    > > here?
    >
    > Does it? Here's what I just did to check that:

    Yes it does, see http://seclists.org/bugtraq/2009/Oct/179


    > # cp /bin/sleep /root/sleep
    >
    > # ls -l /root /root/sleep
    > dr-xr-x---. 19 root root 4096 2009-11-18 07:20 /root
    > -rwxr-xr-x. 1 root root 29152 2009-11-18 07:20 /root/sleep
    >
    > # /root/sleep 600
    >
    > ...then as unprivileged user:
    >
    > $ ps -ef | grep sleep
    > (find pid of sleep program that root is running)
    >
    > $ /proc/5258/exe 600
    > bash: /proc/5258/exe: Permission denied
    >
    > ...it looks like directory permissions are respected here. Did I
    > misunderstand what you're concerned about?

    /proc does not allow you to use /proc/XX/fd of unrelated users; it is
    another mechanism disallowing access. (Plus, I did my experiments with
    /proc/XX/fd, not /exe).
    Pavel
    --
    (english) http://www.livejournal.com/~pavelmachek
    (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html


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