linux-kernel - [REVIEW][PATCH 2/6] vfs: Allow userns root to call mknod on owned filesystems.

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Message-Id: <20180523232538.4880-2-ebiederm@xmission.com>
Date:   Wed, 23 May 2018 18:25:34 -0500
From:   "Eric W. Biederman" <ebiederm@...ssion.com>
To:     Linux Containers <containers@...ts.linux-foundation.org>
Cc:     linux-fsdevel@...r.kernel.org,
        Seth Forshee <seth.forshee@...onical.com>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        Christian Brauner <christian@...uner.io>,
        linux-kernel@...r.kernel.org,
        "Eric W. Biederman" <ebiederm@...ssion.com>
Subject: [REVIEW][PATCH 2/6] vfs: Allow userns root to call mknod on owned filesystems.

These filesystems already always set SB_I_NODEV so mknod will not be
useful for gaining control of any devices no matter their permissions.
This will allow overlayfs and applications to fakeroot to use device
nodes to represent things on disk.

Signed-off-by: "Eric W. Biederman" <ebiederm@...ssion.com>
---
 fs/namei.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/namei.c b/fs/namei.c
index 942c1f096f6b..20335896dcce 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -3679,7 +3679,8 @@ int vfs_mknod(struct inode *dir, struct dentry *dentry, umode_t mode, dev_t dev)
 	if (error)
 		return error;
 
-	if ((S_ISCHR(mode) || S_ISBLK(mode)) && !capable(CAP_MKNOD))
+	if ((S_ISCHR(mode) || S_ISBLK(mode)) &&
+	    !ns_capable(dentry->d_sb->s_user_ns, CAP_MKNOD))
 		return -EPERM;
 
 	if (!dir->i_op->mknod)
-- 
2.14.1