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Message-Id: <1353322222-27060-5-git-send-email-ebiederm@xmission.com>
Date: Mon, 19 Nov 2012 02:50:21 -0800
From: "Eric W. Biederman" <ebiederm@...ssion.com>
To: <linux-fsdevel@...r.kernel.org>
Cc: Linux Containers <containers@...ts.linux-foundation.org>,
<linux-kernel@...r.kernel.org>, Al Viro <viro@...IV.linux.org.uk>,
"Eric W. Biederman" <ebiederm@...ssion.com>
Subject: [PATCH review 5/6] vfs: Allow unprivileged manipulation of the mount namespace.
From: "Eric W. Biederman" <ebiederm@...ssion.com>
- Add a filesystem flag to mark filesystems that are safe to mount as
an unprivileged user.
- Add a filesystem flag to mark filesystems that don't need MNT_NODEV
when mounted by an unprivileged user.
- Relax the permission checks to allow unprivileged users that have
CAP_SYS_ADMIN permissions in the user namespace referred to by the
current mount namespace to be allowed to mount, unmount, and move
filesystems.
Acked-by: "Serge E. Hallyn" <serge@...lyn.com>
Signed-off-by: "Eric W. Biederman" <ebiederm@...ssion.com>
---
fs/namespace.c | 69 ++++++++++++++++++++++++++++++++-------------------
include/linux/fs.h | 2 +
2 files changed, 45 insertions(+), 26 deletions(-)
diff --git a/fs/namespace.c b/fs/namespace.c
index 4dfcaf0..9ddc86f 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -1269,7 +1269,7 @@ SYSCALL_DEFINE2(umount, char __user *, name, int, flags)
goto dput_and_out;
retval = -EPERM;
- if (!capable(CAP_SYS_ADMIN))
+ if (!ns_capable(mnt->mnt_ns->user_ns, CAP_SYS_ADMIN))
goto dput_and_out;
retval = do_umount(mnt, flags);
@@ -1295,7 +1295,7 @@ SYSCALL_DEFINE1(oldumount, char __user *, name)
static int mount_is_safe(struct path *path)
{
- if (capable(CAP_SYS_ADMIN))
+ if (ns_capable(real_mount(path->mnt)->mnt_ns->user_ns, CAP_SYS_ADMIN))
return 0;
return -EPERM;
#ifdef notyet
@@ -1633,7 +1633,7 @@ static int do_change_type(struct path *path, int flag)
int type;
int err = 0;
- if (!capable(CAP_SYS_ADMIN))
+ if (!ns_capable(mnt->mnt_ns->user_ns, CAP_SYS_ADMIN))
return -EPERM;
if (path->dentry != path->mnt->mnt_root)
@@ -1797,7 +1797,7 @@ static int do_move_mount(struct path *path, const char *old_name)
struct mount *p;
struct mount *old;
int err = 0;
- if (!capable(CAP_SYS_ADMIN))
+ if (!ns_capable(real_mount(path->mnt)->mnt_ns->user_ns, CAP_SYS_ADMIN))
return -EPERM;
if (!old_name || !*old_name)
return -EINVAL;
@@ -1884,21 +1884,6 @@ static struct vfsmount *fs_set_subtype(struct vfsmount *mnt, const char *fstype)
return ERR_PTR(err);
}
-static struct vfsmount *
-do_kern_mount(const char *fstype, int flags, const char *name, void *data)
-{
- struct file_system_type *type = get_fs_type(fstype);
- struct vfsmount *mnt;
- if (!type)
- return ERR_PTR(-ENODEV);
- mnt = vfs_kern_mount(type, flags, name, data);
- if (!IS_ERR(mnt) && (type->fs_flags & FS_HAS_SUBTYPE) &&
- !mnt->mnt_sb->s_subtype)
- mnt = fs_set_subtype(mnt, fstype);
- put_filesystem(type);
- return mnt;
-}
-
/*
* add a mount into a namespace's mount tree
*/
@@ -1944,20 +1929,46 @@ unlock:
* create a new mount for userspace and request it to be added into the
* namespace's tree
*/
-static int do_new_mount(struct path *path, const char *type, int flags,
+static int do_new_mount(struct path *path, const char *fstype, int flags,
int mnt_flags, const char *name, void *data)
{
+ struct file_system_type *type;
+ struct user_namespace *user_ns;
struct vfsmount *mnt;
int err;
- if (!type)
+ if (!fstype)
return -EINVAL;
/* we need capabilities... */
- if (!capable(CAP_SYS_ADMIN))
+ user_ns = real_mount(path->mnt)->mnt_ns->user_ns;
+ if (!ns_capable(user_ns, CAP_SYS_ADMIN))
return -EPERM;
- mnt = do_kern_mount(type, flags, name, data);
+ type = get_fs_type(fstype);
+ if (!type)
+ return -ENODEV;
+
+ if (user_ns != &init_user_ns) {
+ if (!(type->fs_flags & FS_USERNS_MOUNT)) {
+ put_filesystem(type);
+ return -EPERM;
+ }
+ /* Only in special cases allow devices from mounts
+ * created outside the initial user namespace.
+ */
+ if (!(type->fs_flags & FS_USERNS_DEV_MOUNT)) {
+ flags |= MS_NODEV;
+ mnt_flags |= MNT_NODEV;
+ }
+ }
+
+ mnt = vfs_kern_mount(type, flags, name, data);
+ if (!IS_ERR(mnt) && (type->fs_flags & FS_HAS_SUBTYPE) &&
+ !mnt->mnt_sb->s_subtype)
+ mnt = fs_set_subtype(mnt, fstype);
+
+ put_filesystem(type);
if (IS_ERR(mnt))
return PTR_ERR(mnt);
@@ -2549,7 +2560,7 @@ SYSCALL_DEFINE2(pivot_root, const char __user *, new_root,
struct mount *new_mnt, *root_mnt;
int error;
- if (!capable(CAP_SYS_ADMIN))
+ if (!ns_capable(current->nsproxy->mnt_ns->user_ns, CAP_SYS_ADMIN))
return -EPERM;
error = user_path_dir(new_root, &new);
@@ -2631,8 +2642,13 @@ static void __init init_mount_tree(void)
struct vfsmount *mnt;
struct mnt_namespace *ns;
struct path root;
+ struct file_system_type *type;
- mnt = do_kern_mount("rootfs", 0, "rootfs", NULL);
+ type = get_fs_type("rootfs");
+ if (!type)
+ panic("Can't find rootfs type");
+ mnt = vfs_kern_mount(type, 0, "rootfs", NULL);
+ put_filesystem(type);
if (IS_ERR(mnt))
panic("Can't create rootfs");
@@ -2757,7 +2773,8 @@ static int mntns_install(struct nsproxy *nsproxy, void *ns)
struct mnt_namespace *mnt_ns = ns;
struct path root;
- if (!capable(CAP_SYS_ADMIN) || !capable(CAP_SYS_CHROOT))
+ if (!ns_capable(mnt_ns->user_ns, CAP_SYS_ADMIN) ||
+ !nsown_capable(CAP_SYS_CHROOT))
return -EINVAL;
if (fs->users != 1)
diff --git a/include/linux/fs.h b/include/linux/fs.h
index b33cfc9..5037aa6 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1812,6 +1812,8 @@ struct file_system_type {
#define FS_REQUIRES_DEV 1
#define FS_BINARY_MOUNTDATA 2
#define FS_HAS_SUBTYPE 4
+#define FS_USERNS_MOUNT 8 /* Can be mounted by userns root */
+#define FS_USERNS_DEV_MOUNT 16 /* A userns mount does not imply MNT_NODEV */
#define FS_REVAL_DOT 16384 /* Check the paths ".", ".." for staleness */
#define FS_RENAME_DOES_D_MOVE 32768 /* FS will handle d_move() during rename() internally. */
struct dentry *(*mount) (struct file_system_type *, int,
--
1.7.5.4
--
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