[Devel] [PATCH RHEL8 COMMIT] ms/saner handling of temporary namespaces
Konstantin Khorenko
khorenko at virtuozzo.com
Tue Sep 22 15:37:58 MSK 2020
The commit is pushed to "branch-rh8-4.18.0-193.6.3.vz8.4.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh8-4.18.0-193.6.3.vz8.4.6
------>
commit 51865b4696675b8be4bdefd61e7b2a3310b6a45d
Author: Al Viro <viro at zeniv.linux.org.uk>
Date: Tue Sep 22 15:37:58 2020 +0300
ms/saner handling of temporary namespaces
Patchset description:
These syscalls were added as preparation step for new mount api (fsopen,
fsconfig, fsmount and fspick will be ported separately).
We can use them to implement "cross-namespace bind-mounting" like this:
fd = open_tree(AT_FDCWD, "/mnt", OPEN_TREE_CLONE);
setns(nsfd, CLONE_NEWNS);
move_mount(fd, "", AT_FDCWD, "/mnt2", MOVE_MOUNT_F_EMPTY_PATH);
This will allow us implementing feature of adding bindmounts to runing
container instead of having unreliable external propagations.
Version for VZ8 is slightly different from VZ7 version.
https://jira.sw.ru/browse/PSBM-107263
Current patch description:
From: Al Viro <viro at zeniv.linux.org.uk>
mount_subtree() creates (and soon destroys) a temporary namespace,
so that automounts could function normally. These beasts should
never become anyone's current namespaces; they don't, but it would
be better to make prevention of that more straightforward. And
since they don't become anyone's current namespace, we don't need
to bother with reserving procfs inums for those.
Teach alloc_mnt_ns() to skip inum allocation if told so, adjust
put_mnt_ns() accordingly, make mount_subtree() use temporary
(anon) namespace. is_anon_ns() checks if a namespace is such.
Signed-off-by: Al Viro <viro at zeniv.linux.org.uk>
(cherry-picked from commit 74e831221cfd79460ec11c1b641093863f0ef3ce)
https://jira.sw.ru/browse/PSBM-107263
Signed-off-by: Pavel Tikhomirov <ptikhomirov at virtuozzo.com>
---
fs/mount.h | 5 ++++
fs/namespace.c | 74 +++++++++++++++++++++++++++-------------------------------
2 files changed, 40 insertions(+), 39 deletions(-)
diff --git a/fs/mount.h b/fs/mount.h
index f39bc9da4d73..6250de544760 100644
--- a/fs/mount.h
+++ b/fs/mount.h
@@ -146,3 +146,8 @@ static inline bool is_local_mountpoint(struct dentry *dentry)
return __is_local_mountpoint(dentry);
}
+
+static inline bool is_anon_ns(struct mnt_namespace *ns)
+{
+ return ns->seq == 0;
+}
diff --git a/fs/namespace.c b/fs/namespace.c
index 1018ae0efa06..22589d59f476 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -2862,7 +2862,8 @@ static void dec_mnt_namespaces(struct ucounts *ucounts)
static void free_mnt_ns(struct mnt_namespace *ns)
{
- ns_free_inum(&ns->ns);
+ if (!is_anon_ns(ns))
+ ns_free_inum(&ns->ns);
dec_mnt_namespaces(ns->ucounts);
put_user_ns(ns->user_ns);
kfree(ns);
@@ -2877,7 +2878,7 @@ static void free_mnt_ns(struct mnt_namespace *ns)
*/
static atomic64_t mnt_ns_seq = ATOMIC64_INIT(1);
-static struct mnt_namespace *alloc_mnt_ns(struct user_namespace *user_ns)
+static struct mnt_namespace *alloc_mnt_ns(struct user_namespace *user_ns, bool anon)
{
struct mnt_namespace *new_ns;
struct ucounts *ucounts;
@@ -2887,28 +2888,27 @@ static struct mnt_namespace *alloc_mnt_ns(struct user_namespace *user_ns)
if (!ucounts)
return ERR_PTR(-ENOSPC);
- new_ns = kmalloc(sizeof(struct mnt_namespace), GFP_KERNEL);
+ new_ns = kzalloc(sizeof(struct mnt_namespace), GFP_KERNEL);
if (!new_ns) {
dec_mnt_namespaces(ucounts);
return ERR_PTR(-ENOMEM);
}
- ret = ns_alloc_inum(&new_ns->ns);
- if (ret) {
- kfree(new_ns);
- dec_mnt_namespaces(ucounts);
- return ERR_PTR(ret);
+ if (!anon) {
+ ret = ns_alloc_inum(&new_ns->ns);
+ if (ret) {
+ kfree(new_ns);
+ dec_mnt_namespaces(ucounts);
+ return ERR_PTR(ret);
+ }
}
new_ns->ns.ops = &mntns_operations;
- new_ns->seq = atomic64_add_return(1, &mnt_ns_seq);
+ if (!anon)
+ new_ns->seq = atomic64_add_return(1, &mnt_ns_seq);
atomic_set(&new_ns->count, 1);
- new_ns->root = NULL;
INIT_LIST_HEAD(&new_ns->list);
init_waitqueue_head(&new_ns->poll);
- new_ns->event = 0;
new_ns->user_ns = get_user_ns(user_ns);
new_ns->ucounts = ucounts;
- new_ns->mounts = 0;
- new_ns->pending_mounts = 0;
return new_ns;
}
@@ -2932,7 +2932,7 @@ struct mnt_namespace *copy_mnt_ns(unsigned long flags, struct mnt_namespace *ns,
old = ns->root;
- new_ns = alloc_mnt_ns(user_ns);
+ new_ns = alloc_mnt_ns(user_ns, false);
if (IS_ERR(new_ns))
return new_ns;
@@ -2987,37 +2987,25 @@ struct mnt_namespace *copy_mnt_ns(unsigned long flags, struct mnt_namespace *ns,
return new_ns;
}
-/**
- * create_mnt_ns - creates a private namespace and adds a root filesystem
- * @mnt: pointer to the new root filesystem mountpoint
- */
-static struct mnt_namespace *create_mnt_ns(struct vfsmount *m)
-{
- struct mnt_namespace *new_ns = alloc_mnt_ns(&init_user_ns);
- if (!IS_ERR(new_ns)) {
- struct mount *mnt = real_mount(m);
- mnt->mnt_ns = new_ns;
- new_ns->root = mnt;
- new_ns->mounts++;
- list_add(&mnt->mnt_list, &new_ns->list);
- } else {
- mntput(m);
- }
- return new_ns;
-}
-
-struct dentry *mount_subtree(struct vfsmount *mnt, const char *name)
+struct dentry *mount_subtree(struct vfsmount *m, const char *name)
{
+ struct mount *mnt = real_mount(m);
struct mnt_namespace *ns;
struct super_block *s;
struct path path;
int err;
- ns = create_mnt_ns(mnt);
- if (IS_ERR(ns))
+ ns = alloc_mnt_ns(&init_user_ns, true);
+ if (IS_ERR(ns)) {
+ mntput(m);
return ERR_CAST(ns);
+ }
+ mnt->mnt_ns = ns;
+ ns->root = mnt;
+ ns->mounts++;
+ list_add(&mnt->mnt_list, &ns->list);
- err = vfs_path_lookup(mnt->mnt_root, mnt,
+ err = vfs_path_lookup(m->mnt_root, m,
name, LOOKUP_FOLLOW|LOOKUP_AUTOMOUNT, &path);
put_mnt_ns(ns);
@@ -3229,6 +3217,7 @@ SYSCALL_DEFINE2(pivot_root, const char __user *, new_root,
static void __init init_mount_tree(void)
{
struct vfsmount *mnt;
+ struct mount *m;
struct mnt_namespace *ns;
struct path root;
struct file_system_type *type;
@@ -3241,10 +3230,14 @@ static void __init init_mount_tree(void)
if (IS_ERR(mnt))
panic("Can't create rootfs");
- ns = create_mnt_ns(mnt);
+ ns = alloc_mnt_ns(&init_user_ns, false);
if (IS_ERR(ns))
panic("Can't allocate initial namespace");
-
+ m = real_mount(mnt);
+ m->mnt_ns = ns;
+ ns->root = m;
+ ns->mounts = 1;
+ list_add(&m->mnt_list, &ns->list);
init_task.nsproxy->mnt_ns = ns;
get_mnt_ns(ns);
@@ -3485,6 +3478,9 @@ static int mntns_install(struct nsproxy *nsproxy, struct ns_common *ns)
!ns_capable(current_user_ns(), CAP_SYS_ADMIN))
return -EPERM;
+ if (is_anon_ns(mnt_ns))
+ return -EINVAL;
+
if (fs->users != 1)
return -EINVAL;
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