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70 lines
2.4 KiB
Diff
70 lines
2.4 KiB
Diff
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From 7415cb7b31569e9266229d4ebc79ccec4841ab04 Mon Sep 17 00:00:00 2001
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From: Serge Hallyn <serge.hallyn@ubuntu.com>
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Date: Fri, 7 Feb 2014 09:32:46 -0600
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Subject: [PATCH] UBUNTU: SAUCE: Overlayfs: allow unprivileged mounts
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Unprivileged mounting, here, refers to root in a non-initial user
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namespace performing the mount. In particular, it requires
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CAP_SYS_ADMIN toward the task's mounts namespace, alleviating
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the concerns of manipulating mount environment for setuid-root
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binaries on the host.
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We refuse unprivileged mounting of most filesystem types because
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we do not trust the in-kernel superblock parsers to correctly
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handle malicious input.
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However, overlayfs does not parse any user-provided data other
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than the pathnames passed in. Therefore unprivileged mounting
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of overlayfs should be safe.
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Allowing unprivileged mounting of overlayfs filesystems would
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allow Ubuntu Trusty users to create overlayfs-based container
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snapshots, which would be a huge usability improvement.
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This patch enables unprivileged mounting of overlayfs.
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I tested a few simple combinations, and found that, when
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doing (the equivalent of)
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mount -t overlayfs -oupperdir=u,lowerdir=l l t
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(u for upper, l for lower, t for target),
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1. overlayfs mount is always allowed, regardless of ownership
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of u, l, or t. However
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2. Creation of new files is allowed so long as u is owned by
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T. Otherwise, regardless of ownerships of l and t it is
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denied. (This is expected; t was the mountpoint and
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'disapears', so its ownership is irrelevant)
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3. modification of a file 'hithere' which is in l but not yet
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in u, and which is not owned by T, is not allowed, even if
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writes to u are allowed. This may be a bug in overlayfs,
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but it is safe behavior. It also will not cause a problem
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for lxc since lxc will ensure that files are mapped into T's
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namespace.
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Signed-off-by: Serge Hallyn <serge.hallyn@ubuntu.com>
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Signed-off-by: Tim Gardner <tim.gardner@canonical.com>
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Signed-off-by: Andy Whitcroft <apw@canonical.com>
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---
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fs/overlayfs/super.c | 1 +
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1 file changed, 1 insertion(+)
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diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
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index 9473e79..50890c2 100644
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--- a/fs/overlayfs/super.c
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+++ b/fs/overlayfs/super.c
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@@ -668,6 +668,7 @@ static struct file_system_type ovl_fs_type = {
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.name = "overlayfs",
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.mount = ovl_mount,
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.kill_sb = kill_anon_super,
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+ .fs_flags = FS_USERNS_MOUNT,
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};
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MODULE_ALIAS_FS("overlayfs");
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--
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2.1.0.rc1
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