4.15-stable review patch. If anyone has any objections, please let me know.
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From: Amir Goldstein amir73il@gmail.com
commit 3ec9b3fafcaf441cc4d46b9742cd6ec0c79f8df0 upstream.
As of now if we encounter an opaque dir while looking for a dentry, we set d->last=true. This means that there is no need to look further in any of the lower layers. This works fine as long as there are no redirets or relative redircts. But what if there is an absolute redirect on the children dentry of opaque directory. We still need to continue to look into next lower layer. This patch fixes it.
Here is an example to demonstrate the issue. Say you have following setup.
upper: /redirect (redirect=/a/b/c) lower1: /a/[b]/c ([b] is opaque) (c has absolute redirect=/a/b/d/) lower0: /a/b/d/foo
Now "redirect" dir should merge with lower1:/a/b/c/ and lower0:/a/b/d. Note, despite the fact lower1:/a/[b] is opaque, we need to continue to look into lower0 because children c has an absolute redirect.
Following is a reproducer.
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@vger.kernel.org #v4.10 Signed-off-by: Amir Goldstein amir73il@gmail.com Signed-off-by: Vivek Goyal vgoyal@redhat.com Signed-off-by: Miklos Szeredi mszeredi@redhat.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- fs/overlayfs/namei.c | 9 +++++++++ 1 file changed, 9 insertions(+)
--- a/fs/overlayfs/namei.c +++ b/fs/overlayfs/namei.c @@ -55,6 +55,15 @@ static int ovl_check_redirect(struct den if (s == next) goto invalid; } + /* + * One of the ancestor path elements in an absolute path + * lookup in ovl_lookup_layer() could have been opaque and + * that will stop further lookup in lower layers (d->stop=true) + * But we have found an absolute redirect in decendant path + * element and that should force continue lookup in lower + * layers (reset d->stop). + */ + d->stop = false; } else { if (strchr(buf, '/') != NULL) goto invalid;