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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Mon, 4 Jul 2022 13:24:48 -0700
Message-ID: <CAHk-=whp8Npc+vMcgbpM9mrPEXkhV4YnhsPxbPXSu9gfEhKWmA@mail.gmail.com>
Subject: Re: [PATCH v4 43/45] namei: initialize parameters passed to step_into()
To:     Al Viro <viro@zeniv.linux.org.uk>
Cc:     Alexander Potapenko <glider@google.com>,
        Alexei Starovoitov <ast@kernel.org>,
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On Mon, Jul 4, 2022 at 12:55 PM Al Viro <viro@zeniv.linux.org.uk> wrote:
>
> You are checking the wrong thing here.  It's really about mount_lock -
> ->d_seq is *not* bumped when we or attach in some namespace.

I think we're talking past each other.

Yes, we need to check the mount sequence lock too, because we're doing
that mount traversal.

But I think we *also* need to check the dentry sequence count, because
the dentry itself could have been moved to another parent.

The two are entirely independent, aren't they?

And the dentry sequence point check should go along with the "we're
now updating the sequence point from the old dentry to the new".

The mount point check should go around the "check dentry mount point",
but it's a separate issue from the whole "we are now jumping to a
different dentry, we should check that the previous dentry hasn't
changed".

                    Linus