pyrox.dev
lol
1From 7415cb7b31569e9266229d4ebc79ccec4841ab04 Mon Sep 17 00:00:00 2001
2From: Serge Hallyn <serge.hallyn@ubuntu.com>
3Date: Fri, 7 Feb 2014 09:32:46 -0600
4Subject: [PATCH] UBUNTU: SAUCE: Overlayfs: allow unprivileged mounts
5
6Unprivileged mounting, here, refers to root in a non-initial user
7namespace performing the mount. In particular, it requires
8CAP_SYS_ADMIN toward the task's mounts namespace, alleviating
9the concerns of manipulating mount environment for setuid-root
10binaries on the host.
11
12We refuse unprivileged mounting of most filesystem types because
13we do not trust the in-kernel superblock parsers to correctly
14handle malicious input.
15
16However, overlayfs does not parse any user-provided data other
17than the pathnames passed in. Therefore unprivileged mounting
18of overlayfs should be safe.
19
20Allowing unprivileged mounting of overlayfs filesystems would
21allow Ubuntu Trusty users to create overlayfs-based container
22snapshots, which would be a huge usability improvement.
23
24This patch enables unprivileged mounting of overlayfs.
25
26I tested a few simple combinations, and found that, when
27doing (the equivalent of)
28
29mount -t overlayfs -oupperdir=u,lowerdir=l l t
30
31(u for upper, l for lower, t for target),
32
331. overlayfs mount is always allowed, regardless of ownership
34of u, l, or t. However
35
362. Creation of new files is allowed so long as u is owned by
37 T. Otherwise, regardless of ownerships of l and t it is
38 denied. (This is expected; t was the mountpoint and
39 'disapears', so its ownership is irrelevant)
40
413. modification of a file 'hithere' which is in l but not yet
42 in u, and which is not owned by T, is not allowed, even if
43 writes to u are allowed. This may be a bug in overlayfs,
44 but it is safe behavior. It also will not cause a problem
45 for lxc since lxc will ensure that files are mapped into T's
46 namespace.
47
48Signed-off-by: Serge Hallyn <serge.hallyn@ubuntu.com>
49Signed-off-by: Tim Gardner <tim.gardner@canonical.com>
50Signed-off-by: Andy Whitcroft <apw@canonical.com>
51---
52 fs/overlayfs/super.c | 1 +
53 1 file changed, 1 insertion(+)
54
55diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
56index 9473e79..50890c2 100644
57--- a/fs/overlayfs/super.c
58+++ b/fs/overlayfs/super.c
59@@ -668,6 +668,7 @@ static struct file_system_type ovl_fs_type = {
60 .name = "overlayfs",
61 .mount = ovl_mount,
62 .kill_sb = kill_anon_super,
63+ .fs_flags = FS_USERNS_MOUNT,
64 };
65 MODULE_ALIAS_FS("overlayfs");
66
67--
682.1.0.rc1
69