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    SubjectRe: [PATCH 2/2] vfs: force reval on dentry of bind mounted files on FS_REVAL_DOT filesystems
    Jeff Layton <jlayton@redhat.com> writes:

    > In the case of a bind mounted file, the path walking code will assume
    > that the cached dentry that was bind mounted is valid. This is a problem
    > problem for NFSv4 in a way that's similar to LAST_BIND symlinks.
    >
    > Fix this by revalidating the dentry if FS_FOLLOW_DOT is set and
    > __follow_mount returns true.
    >
    > Note that in the non-open codepath, we cannot return an error to the
    > lookup if the revalidation fails. Doing so will leave a bind mount in
    > a state such that we can't unmount it. In that case we'll just have to
    > settle for d_invalidating it (which should mostly turn out to be a
    > d_drop in this case) and returning success.

    Looks reasonable to me. I wonder a little if we care about follow_mount
    as well as __follow_mount.

    This seems reasonable to me.

    Acked-by: "Eric W. Biederman" <ebiederm@xmission.com>

    >
    > Signed-off-by: Jeff Layton <jlayton@redhat.com>
    > ---
    > fs/namei.c | 11 ++++++++++-
    > 1 files changed, 10 insertions(+), 1 deletions(-)
    >
    > diff --git a/fs/namei.c b/fs/namei.c
    > index 339789e..0d55b6f 100644
    > --- a/fs/namei.c
    > +++ b/fs/namei.c
    > @@ -851,7 +851,13 @@ static int do_lookup(struct nameidata *nd, struct qstr *name,
    > done:
    > path->mnt = mnt;
    > path->dentry = dentry;
    > - __follow_mount(path);
    > +
    > + /*
    > + * cannot return the error returned by force_reval_path as that can
    > + * make it impossible to unmount a bind mounted dentry if it's stale.
    > + */
    > + if (__follow_mount(path))
    > + force_reval_path(path, nd);
    > return 0;
    >
    > need_lookup:
    > @@ -1840,6 +1846,9 @@ do_last:
    > error = -ELOOP;
    > if (flag & O_NOFOLLOW)
    > goto exit_dput;
    > + error = force_reval_path(&path, &nd);
    > + if (error)
    > + goto exit_dput;
    > }
    >
    > error = -ENOENT;
    > --
    > 1.5.5.6


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