The only way to explain the problem is with an example.
Watch me make foo disappear:
$ 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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