[PATCH v13 1/5] overlayfs: check CAP_DAC_READ_SEARCH before issuing exportfs_decode_fh

[Mark Salyzyn via Linux-f2fs-devel <linux-f2fs-devel@lists.sourceforge.net>]

Assumption never checked, should fail if the mounter creds are not
sufficient.

Signed-off-by: Mark Salyzyn <salyzyn@android.com>
Cc: Miklos Szeredi <miklos@szeredi.hu>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Vivek Goyal <vgoyal@redhat.com>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Cc: Amir Goldstein <amir73il@gmail.com>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: Stephen Smalley <sds@tycho.nsa.gov>
Cc: linux-unionfs@vger.kernel.org
Cc: linux-doc@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: kernel-team@android.com
Cc: Eric Van Hensbergen <ericvh@gmail.com>
Cc: Latchesar Ionkov <lucho@ionkov.net>
Cc: Dominique Martinet <asmadeus@codewreck.org>
Cc: David Howells <dhowells@redhat.com>
Cc: Chris Mason <clm@fb.com>
Cc: Josef Bacik <josef@toxicpanda.com>
Cc: David Sterba <dsterba@suse.com>
Cc: Jeff Layton <jlayton@kernel.org>
Cc: Sage Weil <sage@redhat.com>
Cc: Ilya Dryomov <idryomov@gmail.com>
Cc: Steve French <sfrench@samba.org>
Cc: Tyler Hicks <tyhicks@canonical.com>
Cc: Jan Kara <jack@suse.com>
Cc: Theodore Ts'o <tytso@mit.edu>
Cc: Andreas Dilger <adilger.kernel@dilger.ca>
Cc: Jaegeuk Kim <jaegeuk@kernel.org>
Cc: Chao Yu <yuchao0@huawei.com>
Cc: Bob Peterson <rpeterso@redhat.com>
Cc: Andreas Gruenbacher <agruenba@redhat.com>
Cc: David Woodhouse <dwmw2@infradead.org>
Cc: Richard Weinberger <richard@nod.at>
Cc: Dave Kleikamp <shaggy@kernel.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Tejun Heo <tj@kernel.org>
Cc: Trond Myklebust <trond.myklebust@hammerspace.com>
Cc: Anna Schumaker <anna.schumaker@netapp.com>
Cc: Mark Fasheh <mark@fasheh.com>
Cc: Joel Becker <jlbec@evilplan.org>
Cc: Joseph Qi <joseph.qi@linux.alibaba.com>
Cc: Mike Marshall <hubcap@omnibond.com>
Cc: Martin Brandenburg <martin@omnibond.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Phillip Lougher <phillip@squashfs.org.uk>
Cc: Darrick J. Wong <darrick.wong@oracle.com>
Cc: linux-xfs@vger.kernel.org
Cc: Hugh Dickins <hughd@google.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Mathieu Malaterre <malat@debian.org>
Cc: Ernesto A. Fern√°ndez <ernesto.mnd.fernandez@gmail.com>
Cc: Vyacheslav Dubeyko <slava@dubeyko.com>
Cc: v9fs-developer@lists.sourceforge.net
Cc: linux-afs@lists.infradead.org
Cc: linux-btrfs@vger.kernel.org
Cc: ceph-devel@vger.kernel.org
Cc: linux-cifs@vger.kernel.org
Cc: samba-technical@lists.samba.org
Cc: ecryptfs@vger.kernel.org
Cc: linux-ext4@vger.kernel.org
Cc: linux-f2fs-devel@lists.sourceforge.net
Cc: linux-fsdevel@vger.kernel.org
Cc: cluster-devel@redhat.com
Cc: linux-mtd@lists.infradead.org
Cc: jfs-discussion@lists.sourceforge.net
Cc: linux-nfs@vger.kernel.org
Cc: ocfs2-devel@oss.oracle.com
Cc: devel@lists.orangefs.org
Cc: reiserfs-devel@vger.kernel.org
Cc: linux-mm@kvack.org
Cc: netdev@vger.kernel.org
Cc: linux-security-module@vger.kernel.org
Cc: stable@vger.kernel.org # 4.4, 4.9, 4.14 & 4.19
---
v11 + v12 + v13 - rebase

v10:
- return NULL rather than ERR_PTR(-EPERM)
- did _not_ add it ovl_can_decode_fh() because of changes since last
  review, suspect needs to be added to ovl_lower_uuid_ok()?

v8 + v9:
- rebase

v7:
- This time for realz

v6:
- rebase

v5:
- dependency of "overlayfs: override_creds=off option bypass creator_cred"
---
 fs/overlayfs/namei.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/fs/overlayfs/namei.c b/fs/overlayfs/namei.c
index e9717c2f7d45..9702f0d5309d 100644
--- a/fs/overlayfs/namei.c
+++ b/fs/overlayfs/namei.c
@@ -161,6 +161,9 @@ struct dentry *ovl_decode_real_fh(struct ovl_fh *fh, struct vfsmount *mnt,
 	if (!uuid_equal(&fh->uuid, &mnt->mnt_sb->s_uuid))
 		return NULL;
 
+	if (!capable(CAP_DAC_READ_SEARCH))
+		return NULL;
+
 	bytes = (fh->len - offsetof(struct ovl_fh, fid));
 	real = exportfs_decode_fh(mnt, (struct fid *)fh->fid,
 				  bytes >> 2, (int)fh->type,
-- 
2.22.0.770.g0f2c4a37fd-goog



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