linux-kernel - [PATCH 4.9 25/35] nfsd4: readdirplus shouldnt return parent of export

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <20210122135733.324059563@linuxfoundation.org>
Date:   Fri, 22 Jan 2021 15:10:27 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Youjipeng <wangzhibei1999@...il.com>,
        "J. Bruce Fields" <bfields@...hat.com>,
        Chuck Lever <chuck.lever@...cle.com>
Subject: [PATCH 4.9 25/35] nfsd4: readdirplus shouldnt return parent of export

From: J. Bruce Fields <bfields@...hat.com>

commit 51b2ee7d006a736a9126e8111d1f24e4fd0afaa6 upstream.

If you export a subdirectory of a filesystem, a READDIRPLUS on the root
of that export will return the filehandle of the parent with the ".."
entry.

The filehandle is optional, so let's just not return the filehandle for
".." if we're at the root of an export.

Note that once the client learns one filehandle outside of the export,
they can trivially access the rest of the export using further lookups.

However, it is also not very difficult to guess filehandles outside of
the export.  So exporting a subdirectory of a filesystem should
considered equivalent to providing access to the entire filesystem.  To
avoid confusion, we recommend only exporting entire filesystems.

Reported-by: Youjipeng <wangzhibei1999@...il.com>
Signed-off-by: J. Bruce Fields <bfields@...hat.com>
Cc: stable@...r.kernel.org
Signed-off-by: Chuck Lever <chuck.lever@...cle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 fs/nfsd/nfs3xdr.c |    7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

--- a/fs/nfsd/nfs3xdr.c
+++ b/fs/nfsd/nfs3xdr.c
@@ -822,9 +822,14 @@ compose_entry_fh(struct nfsd3_readdirres
 	if (isdotent(name, namlen)) {
 		if (namlen == 2) {
 			dchild = dget_parent(dparent);
-			/* filesystem root - cannot return filehandle for ".." */
+			/*
+			 * Don't return filehandle for ".." if we're at
+			 * the filesystem or export root:
+			 */
 			if (dchild == dparent)
 				goto out;
+			if (dparent == exp->ex_path.dentry)
+				goto out;
 		} else
 			dchild = dget(dparent);
 	} else