On Thu, Mar 08, 2018 at 11:31:40PM +0200, Amir Goldstein wrote:
> The only way to explain the problem is with an example.
> Watch me make foo disappear:
Hi Amir,
I will look at it tomorrow more closely. I am also about to send 3 RFC
fixes for the issues we discussed. Please have a look and see what do you
think.
Vivek
>
> $ mkdir lower middle upper work work2 merged
> $ mkdir lower/origin
> $ touch lower/origin/foo
> $ mount -t overlay none merged/ \
> -olowerdir=lower,upperdir=middle,workdir=work2
> $ mkdir merged/pure
> $ mv merged/origin merged/pure/redirect
> $ umount merged
> $ mount -t overlay none merged/ \
> -olowerdir=middle:lower,upperdir=upper,workdir=work
> $ mv merged/pure/redirect merged/redirect
>
> Now you see foo inside a twice redirected merged dir:
>
> $ ls merged/redirect
> foo
> $ umount merged
> $ mount -t overlay none merged/ \
> -olowerdir=middle:lower,upperdir=upper,workdir=work
>
> After mount cycle you don't see foo inside the same dir:
>
> $ ls merged/redirect
>
> During middle layer lookup, the opaqueness of middle/pure is left in
> the lookup state and then middle/pure/redirect is wrongly treated as
> opaque.
>
> Fixes: 02b69b284cd7 ("ovl: lookup redirects")
> Cc: <stable@xxxxxxxxxxxxxxx> #v4.10
> Signed-off-by: Amir Goldstein <amir73il@xxxxxxxxx>
> ---
>
> Vivek,
>
> This is the bug I was talking about in review of metacopy lookup.
>
> Miklos,
>
> This change seems a bit subtle... besides the reproducer I sanity tested
> redirects with unionmount-testsuite ./run --ov=10 and the overlay/quick
> xfstests. Neither would have hit this sort of corner case though.
> I will add a test to cover this case later on.
>
> Thanks,
> Amir.
>
> fs/overlayfs/namei.c | 8 ++++++++
> 1 file changed, 8 insertions(+)
>
> diff --git a/fs/overlayfs/namei.c b/fs/overlayfs/namei.c
> index 70fcfcc684cc..31ca563b7666 100644
> --- a/fs/overlayfs/namei.c
> +++ b/fs/overlayfs/namei.c
> @@ -51,6 +51,14 @@ static int ovl_check_redirect(struct dentry *dentry, struct ovl_lookup_data *d,
> if (res == 0)
> goto invalid;
> if (buf[0] == '/') {
> + /*
> + * One of the ancestor path elements in an absolute path
> + * lookup in ovl_lookup_layer() could have been opaque, but it
> + * possible for a decendant path element to reset opaqueness in
> + * case this path element has an absolute redirect to a lower
> + * layer.
> + */
> + d->stop = d->opaque = false;
> for (s = buf; *s++ == '/'; s = next) {
> next = strchrnul(s, '/');
> if (s == next)
> --
> 2.7.4
>
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