linux-kernel - [PATCH v5 2/3] overlayfs: check CAP_MKNOD before issuing vfs

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Message-Id: <20180828165319.211563-1-salyzyn@android.com>
Date:   Tue, 28 Aug 2018 09:53:16 -0700
From:   Mark Salyzyn <salyzyn@...roid.com>
To:     linux-kernel@...r.kernel.org
Cc:     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 v5 2/3] overlayfs: check CAP_MKNOD before issuing vfs_whiteout

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

v5
- dependency of "overlayfs: override_creds=off option bypass creator_cred"
---
 fs/overlayfs/overlayfs.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/overlayfs/overlayfs.h b/fs/overlayfs/overlayfs.h
index 7538b9b56237..bf3a80157d42 100644
--- a/fs/overlayfs/overlayfs.h
+++ b/fs/overlayfs/overlayfs.h
@@ -176,7 +176,7 @@ static inline int ovl_do_rename(struct inode *olddir, struct dentry *olddentry,
 
 static inline int ovl_do_whiteout(struct inode *dir, struct dentry *dentry)
 {
-	int err = vfs_whiteout(dir, dentry);
+	int err = capable(CAP_MKNOD) ? vfs_whiteout(dir, dentry) : -EPERM;
 	pr_debug("whiteout(%pd2) = %i\n", dentry, err);
 	return err;
 }
-- 
2.19.0.rc0.228.g281dcd1b4d0-goog