linux-kernel - [PATCH v12 1/5] overlayfs: check CAP_DAC_READ_SEARCH before issuing exportfs_decode

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Message-Id: <20190730172904.79146-2-salyzyn@android.com>
Date:   Tue, 30 Jul 2019 10:28:58 -0700
From:   Mark Salyzyn <salyzyn@...roid.com>
To:     linux-kernel@...r.kernel.org
Cc:     kernel-team@...roid.com, Mark Salyzyn <salyzyn@...roid.com>,
        Miklos Szeredi <miklos@...redi.hu>,
        Jonathan Corbet <corbet@....net>,
        Vivek Goyal <vgoyal@...hat.com>,
        "Eric W . Biederman" <ebiederm@...ssion.com>,
        Amir Goldstein <amir73il@...il.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Stephen Smalley <sds@...ho.nsa.gov>,
        linux-unionfs@...r.kernel.org, linux-doc@...r.kernel.org
Subject: [PATCH v12 1/5] overlayfs: check CAP_DAC_READ_SEARCH before issuing exportfs_decode_fh

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

Signed-off-by: Mark Salyzyn <salyzyn@...roid.com>
Cc: Miklos Szeredi <miklos@...redi.hu>
Cc: Jonathan Corbet <corbet@....net>
Cc: Vivek Goyal <vgoyal@...hat.com>
Cc: Eric W. Biederman <ebiederm@...ssion.com>
Cc: Amir Goldstein <amir73il@...il.com>
Cc: Randy Dunlap <rdunlap@...radead.org>
Cc: Stephen Smalley <sds@...ho.nsa.gov>
Cc: linux-unionfs@...r.kernel.org
Cc: linux-doc@...r.kernel.org
Cc: linux-kernel@...r.kernel.org
Cc: kernel-team@...roid.com
---
v11 + v12 - 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