[PATCH v2 2/4] nsproxy: add struct nsset

From: Christian Brauner
Date: Thu Apr 30 2020 - 12:57:38 EST

Add a simple struct nsset. It holds all necessary pieces to switch to a new
set of namespaces without leaving a task in a half-switched state which we
will make use of in the next patch. This patch simply switches the existing
setns logic over without causing a change in setns() behavior. This brings
setns() closer to how unshare() works().

Cc: Eric W. Biederman <ebiederm@xxxxxxxxxxxx>
Cc: Serge Hallyn <serge@xxxxxxxxxx>
Signed-off-by: Christian Brauner <christian.brauner@xxxxxxxxxx>
---
/* v2 */
patch introduced
---
fs/namespace.c | 17 +++++--
include/linux/mnt_namespace.h | 2 +
include/linux/nsproxy.h | 24 +++++++++
include/linux/proc_ns.h | 4 +-
ipc/namespace.c | 9 ++--
kernel/cgroup/namespace.c | 7 +--
kernel/nsproxy.c | 94 ++++++++++++++++++++++++++++++-----
kernel/pid_namespace.c | 7 +--
kernel/time/namespace.c | 7 +--
kernel/user_namespace.c | 8 +--
kernel/utsname.c | 7 +--
net/core/net_namespace.c | 7 +--
12 files changed, 150 insertions(+), 43 deletions(-)

diff --git a/fs/namespace.c b/fs/namespace.c
index a28e4db075ed..91d2b86aadfb 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -1733,6 +1733,11 @@ static struct mnt_namespace *to_mnt_ns(struct ns_common *ns)
return container_of(ns, struct mnt_namespace, ns);
}

+struct ns_common *mnt_ns_to_common(struct mnt_namespace *mnt)
+{
+ return &mnt->ns;
+}
+
static bool mnt_ns_loop(struct dentry *dentry)
{
/* Could bind mounting the mount namespace inode cause a
@@ -3954,16 +3959,18 @@ static void mntns_put(struct ns_common *ns)
put_mnt_ns(to_mnt_ns(ns));
}

-static int mntns_install(struct nsproxy *nsproxy, struct ns_common *ns)
+static int mntns_install(struct nsset *nsset, struct ns_common *ns)
{
- struct fs_struct *fs = current->fs;
+ struct nsproxy *nsproxy = nsset->nsproxy;
+ struct fs_struct *fs = nsset->fs;
struct mnt_namespace *mnt_ns = to_mnt_ns(ns), *old_mnt_ns;
+ struct user_namespace *user_ns = nsset->cred->user_ns;
struct path root;
int err;

- if (!ns_capable(mnt_ns->user_ns, CAP_SYS_ADMIN) ||
- !ns_capable(current_user_ns(), CAP_SYS_CHROOT) ||
- !ns_capable(current_user_ns(), CAP_SYS_ADMIN))
+ if (!ns_capable_cred(nsset->cred, mnt_ns->user_ns, CAP_SYS_ADMIN) ||
+ !ns_capable_cred(nsset->cred, user_ns, CAP_SYS_CHROOT) ||
+ !ns_capable_cred(nsset->cred, user_ns, CAP_SYS_ADMIN))
return -EPERM;

if (is_anon_ns(mnt_ns))
diff --git a/include/linux/mnt_namespace.h b/include/linux/mnt_namespace.h
index 35942084cd40..664dd3b06f34 100644
--- a/include/linux/mnt_namespace.h
+++ b/include/linux/mnt_namespace.h
@@ -6,10 +6,12 @@
struct mnt_namespace;
struct fs_struct;
struct user_namespace;
+struct ns_common;

extern struct mnt_namespace *copy_mnt_ns(unsigned long, struct mnt_namespace *,
struct user_namespace *, struct fs_struct *);
extern void put_mnt_ns(struct mnt_namespace *ns);
+extern struct ns_common *mnt_ns_to_common(struct mnt_namespace *);

extern const struct file_operations proc_mounts_operations;
extern const struct file_operations proc_mountinfo_operations;
diff --git a/include/linux/nsproxy.h b/include/linux/nsproxy.h
index 074f395b9ad2..cdb171efc7cb 100644
--- a/include/linux/nsproxy.h
+++ b/include/linux/nsproxy.h
@@ -41,6 +41,30 @@ struct nsproxy {
};
extern struct nsproxy init_nsproxy;

+/*
+ * A structure to encompass all bits needed to install
+ * a partial or complete new set of namespaces.
+ *
+ * If a new user namespace is requested cred will
+ * point to a modifiable set of credentials. If a pointer
+ * to a modifiable set is needed nsset_cred() must be
+ * used and tested.
+ */
+struct nsset {
+ unsigned flags;
+ struct nsproxy *nsproxy;
+ struct fs_struct *fs;
+ const struct cred *cred;
+};
+
+static inline struct cred *nsset_cred(struct nsset *set)
+{
+ if (set->flags & CLONE_NEWUSER)
+ return (struct cred *)set->cred;
+
+ return NULL;
+}
+
/*
* the namespaces access rules are:
*
diff --git a/include/linux/proc_ns.h b/include/linux/proc_ns.h
index 6abe85c34681..75807ecef880 100644
--- a/include/linux/proc_ns.h
+++ b/include/linux/proc_ns.h
@@ -8,7 +8,7 @@
#include <linux/ns_common.h>

struct pid_namespace;
-struct nsproxy;
+struct nsset;
struct path;
struct task_struct;
struct inode;
@@ -19,7 +19,7 @@ struct proc_ns_operations {
int type;
struct ns_common *(*get)(struct task_struct *task);
void (*put)(struct ns_common *ns);
- int (*install)(struct nsproxy *nsproxy, struct ns_common *ns);
+ int (*install)(struct nsset *nsset, struct ns_common *ns);
struct user_namespace *(*owner)(struct ns_common *ns);
struct ns_common *(*get_parent)(struct ns_common *ns);
} __randomize_layout;
diff --git a/ipc/namespace.c b/ipc/namespace.c
index b3ca1476ca51..df6aa2deab18 100644
--- a/ipc/namespace.c
+++ b/ipc/namespace.c
@@ -177,15 +177,14 @@ static void ipcns_put(struct ns_common *ns)
return put_ipc_ns(to_ipc_ns(ns));
}

-static int ipcns_install(struct nsproxy *nsproxy, struct ns_common *new)
+static int ipcns_install(struct nsset *nsset, struct ns_common *new)
{
+ struct nsproxy *nsproxy = nsset->nsproxy;
struct ipc_namespace *ns = to_ipc_ns(new);
- if (!ns_capable(ns->user_ns, CAP_SYS_ADMIN) ||
- !ns_capable(current_user_ns(), CAP_SYS_ADMIN))
+ if (!ns_capable_cred(nsset->cred, ns->user_ns, CAP_SYS_ADMIN) ||
+ !ns_capable_cred(nsset->cred, nsset->cred->user_ns, CAP_SYS_ADMIN))
return -EPERM;

- /* Ditch state from the old ipc namespace */
- exit_sem(current);
put_ipc_ns(nsproxy->ipc_ns);
nsproxy->ipc_ns = get_ipc_ns(ns);
return 0;
diff --git a/kernel/cgroup/namespace.c b/kernel/cgroup/namespace.c
index b05f1dd58a62..01279c9e6dee 100644
--- a/kernel/cgroup/namespace.c
+++ b/kernel/cgroup/namespace.c
@@ -95,12 +95,13 @@ static inline struct cgroup_namespace *to_cg_ns(struct ns_common *ns)
return container_of(ns, struct cgroup_namespace, ns);
}

-static int cgroupns_install(struct nsproxy *nsproxy, struct ns_common *ns)
+static int cgroupns_install(struct nsset *nsset, struct ns_common *ns)
{
+ struct nsproxy *nsproxy = nsset->nsproxy;
struct cgroup_namespace *cgroup_ns = to_cg_ns(ns);

- if (!ns_capable(current_user_ns(), CAP_SYS_ADMIN) ||
- !ns_capable(cgroup_ns->user_ns, CAP_SYS_ADMIN))
+ if (!ns_capable_cred(nsset->cred, nsset->cred->user_ns, CAP_SYS_ADMIN) ||
+ !ns_capable_cred(nsset->cred, cgroup_ns->user_ns, CAP_SYS_ADMIN))
return -EPERM;

/* Don't need to do anything if we are attaching to our own cgroupns. */
diff --git a/kernel/nsproxy.c b/kernel/nsproxy.c
index ed9882108cd2..2da463bab58a 100644
--- a/kernel/nsproxy.c
+++ b/kernel/nsproxy.c
@@ -19,6 +19,7 @@
#include <net/net_namespace.h>
#include <linux/ipc_namespace.h>
#include <linux/time_namespace.h>
+#include <linux/fs_struct.h>
#include <linux/proc_ns.h>
#include <linux/file.h>
#include <linux/syscalls.h>
@@ -257,12 +258,85 @@ void exit_task_namespaces(struct task_struct *p)
switch_task_namespaces(p, NULL);
}

+static void put_nsset(struct nsset *nsset)
+{
+ unsigned flags = nsset->flags;
+
+ if (flags & CLONE_NEWUSER)
+ put_cred(nsset_cred(nsset));
+ if (nsset->nsproxy)
+ free_nsproxy(nsset->nsproxy);
+}
+
+static int prepare_nsset(unsigned flags, struct nsset *nsset)
+{
+ struct task_struct *me = current;
+
+ nsset->nsproxy = create_new_namespaces(0, me, current_user_ns(), me->fs);
+ if (IS_ERR(nsset->nsproxy))
+ return PTR_ERR(nsset->nsproxy);
+
+ if (flags & CLONE_NEWUSER)
+ nsset->cred = prepare_creds();
+ else
+ nsset->cred = current_cred();
+ if (!nsset->cred)
+ goto out;
+
+ if (flags & CLONE_NEWNS)
+ nsset->fs = me->fs;
+
+ nsset->flags = flags;
+ return 0;
+
+out:
+ put_nsset(nsset);
+ return -ENOMEM;
+}
+
+/*
+ * This is the point of no return. There are just a few namespaces
+ * that do some actual work here and it's sufficiently minimal that
+ * a separate ns_common operation seems unnecessary for now.
+ * Unshare is doing the same thing. If we'll end up needing to do
+ * more in a given namespace or a helper here is ultimately not
+ * exported anymore a simple commit handler for each namespace
+ * should be added to ns_common.
+ */
+static void commit_nsset(struct nsset *nsset)
+{
+ unsigned flags = nsset->flags;
+ struct task_struct *me = current;
+
+#ifdef CONFIG_USER_NS
+ if (flags & CLONE_NEWUSER) {
+ /* transfer ownership */
+ commit_creds(nsset_cred(nsset));
+ nsset->cred = NULL;
+ }
+#endif
+
+#ifdef CONFIG_IPC_NS
+ if (flags & CLONE_NEWIPC)
+ exit_sem(me);
+#endif
+
+ /* transfer ownership */
+ switch_task_namespaces(me, nsset->nsproxy);
+ nsset->nsproxy = NULL;
+}
+
+static inline int validate_ns(struct nsset *nsset, struct ns_common *ns)
+{
+ return ns->ops->install(nsset, ns);
+}
+
SYSCALL_DEFINE2(setns, int, fd, int, nstype)
{
struct task_struct *tsk = current;
- struct nsproxy *new_nsproxy;
struct file *file;
struct ns_common *ns;
+ struct nsset nsset = {};
int err;

file = proc_ns_fget(fd);
@@ -274,20 +348,16 @@ SYSCALL_DEFINE2(setns, int, fd, int, nstype)
if (nstype && (ns->ops->type != nstype))
goto out;

- new_nsproxy = create_new_namespaces(0, tsk, current_user_ns(), tsk->fs);
- if (IS_ERR(new_nsproxy)) {
- err = PTR_ERR(new_nsproxy);
+ err = prepare_nsset(nstype, &nsset);
+ if (err)
goto out;
- }

- err = ns->ops->install(new_nsproxy, ns);
- if (err) {
- free_nsproxy(new_nsproxy);
- goto out;
+ err = validate_ns(&nsset, ns);
+ if (!err) {
+ commit_nsset(&nsset);
+ perf_event_namespaces(tsk);
}
- switch_task_namespaces(tsk, new_nsproxy);
-
- perf_event_namespaces(tsk);
+ put_nsset(&nsset);
out:
fput(file);
return err;
diff --git a/kernel/pid_namespace.c b/kernel/pid_namespace.c
index 01f8ba32cc0c..b0b0e1055812 100644
--- a/kernel/pid_namespace.c
+++ b/kernel/pid_namespace.c
@@ -378,13 +378,14 @@ static void pidns_put(struct ns_common *ns)
put_pid_ns(to_pid_ns(ns));
}

-static int pidns_install(struct nsproxy *nsproxy, struct ns_common *ns)
+static int pidns_install(struct nsset *nsset, struct ns_common *ns)
{
+ struct nsproxy *nsproxy = nsset->nsproxy;
struct pid_namespace *active = task_active_pid_ns(current);
struct pid_namespace *ancestor, *new = to_pid_ns(ns);

- if (!ns_capable(new->user_ns, CAP_SYS_ADMIN) ||
- !ns_capable(current_user_ns(), CAP_SYS_ADMIN))
+ if (!ns_capable_cred(nsset->cred, new->user_ns, CAP_SYS_ADMIN) ||
+ !ns_capable_cred(nsset->cred, nsset->cred->user_ns, CAP_SYS_ADMIN))
return -EPERM;

/*
diff --git a/kernel/time/namespace.c b/kernel/time/namespace.c
index 53bce347cd50..8ff16ef947ef 100644
--- a/kernel/time/namespace.c
+++ b/kernel/time/namespace.c
@@ -280,16 +280,17 @@ static void timens_put(struct ns_common *ns)
put_time_ns(to_time_ns(ns));
}

-static int timens_install(struct nsproxy *nsproxy, struct ns_common *new)
+static int timens_install(struct nsset *nsset, struct ns_common *new)
{
+ struct nsproxy *nsproxy = nsset->nsproxy;
struct time_namespace *ns = to_time_ns(new);
int err;

if (!current_is_single_threaded())
return -EUSERS;

- if (!ns_capable(ns->user_ns, CAP_SYS_ADMIN) ||
- !ns_capable(current_user_ns(), CAP_SYS_ADMIN))
+ if (!ns_capable_cred(nsset->cred, ns->user_ns, CAP_SYS_ADMIN) ||
+ !ns_capable_cred(nsset->cred, nsset->cred->user_ns, CAP_SYS_ADMIN))
return -EPERM;

timens_set_vvar_page(current, ns);
diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
index 8eadadc478f9..87804e0371fe 100644
--- a/kernel/user_namespace.c
+++ b/kernel/user_namespace.c
@@ -1253,7 +1253,7 @@ static void userns_put(struct ns_common *ns)
put_user_ns(to_user_ns(ns));
}

-static int userns_install(struct nsproxy *nsproxy, struct ns_common *ns)
+static int userns_install(struct nsset *nsset, struct ns_common *ns)
{
struct user_namespace *user_ns = to_user_ns(ns);
struct cred *cred;
@@ -1274,14 +1274,14 @@ static int userns_install(struct nsproxy *nsproxy, struct ns_common *ns)
if (!ns_capable(user_ns, CAP_SYS_ADMIN))
return -EPERM;

- cred = prepare_creds();
+ cred = nsset_cred(nsset);
if (!cred)
- return -ENOMEM;
+ return -EINVAL;

put_user_ns(cred->user_ns);
set_cred_user_ns(cred, get_user_ns(user_ns));

- return commit_creds(cred);
+ return 0;
}

struct ns_common *ns_get_owner(struct ns_common *ns)
diff --git a/kernel/utsname.c b/kernel/utsname.c
index f0e491193009..f8fa76756022 100644
--- a/kernel/utsname.c
+++ b/kernel/utsname.c
@@ -140,12 +140,13 @@ static void utsns_put(struct ns_common *ns)
put_uts_ns(to_uts_ns(ns));
}

-static int utsns_install(struct nsproxy *nsproxy, struct ns_common *new)
+static int utsns_install(struct nsset *nsset, struct ns_common *new)
{
+ struct nsproxy *nsproxy = nsset->nsproxy;
struct uts_namespace *ns = to_uts_ns(new);

- if (!ns_capable(ns->user_ns, CAP_SYS_ADMIN) ||
- !ns_capable(current_user_ns(), CAP_SYS_ADMIN))
+ if (!ns_capable_cred(nsset->cred, ns->user_ns, CAP_SYS_ADMIN) ||
+ !ns_capable_cred(nsset->cred, nsset->cred->user_ns, CAP_SYS_ADMIN))
return -EPERM;

get_uts_ns(ns);
diff --git a/net/core/net_namespace.c b/net/core/net_namespace.c
index 190ca66a383b..e312a5f411ae 100644
--- a/net/core/net_namespace.c
+++ b/net/core/net_namespace.c
@@ -1353,12 +1353,13 @@ static void netns_put(struct ns_common *ns)
put_net(to_net_ns(ns));
}

-static int netns_install(struct nsproxy *nsproxy, struct ns_common *ns)
+static int netns_install(struct nsset *nsset, struct ns_common *ns)
{
+ struct nsproxy *nsproxy = nsset->nsproxy;
struct net *net = to_net_ns(ns);

- if (!ns_capable(net->user_ns, CAP_SYS_ADMIN) ||
- !ns_capable(current_user_ns(), CAP_SYS_ADMIN))
+ if (!ns_capable_cred(nsset->cred, net->user_ns, CAP_SYS_ADMIN) ||
+ !ns_capable_cred(nsset->cred, nsset->cred->user_ns, CAP_SYS_ADMIN))
return -EPERM;

put_net(nsproxy->net_ns);
--
2.26.2