nsproxy: add struct nsset

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 switches the existing setns
logic over without causing a change in setns() behavior. This brings
setns() closer to how unshare() works(). The prepare_ns() function is
responsible to prepare all necessary information. This has two reasons.
First it minimizes dependencies between individual namespaces, i.e. all
install handler can expect that all fields are properly initialized
independent in what order they are called in. Second, this makes the code
easier to maintain and easier to follow if it needs to be changed.

The prepare_ns() helper will only be switched over to use a flags argument
in the next patch. Here it will still use nstype as a simple integer
argument which was argued would be clearer. I'm not particularly
opinionated about this if it really helps or not. The struct nsset itself
already contains the flags field since its name already indicates that it
can contain information required by different namespaces. None of this
should have functional consequences.

Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
Reviewed-by: Serge Hallyn <serge@hallyn.com>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Cc: Serge Hallyn <serge@hallyn.com>
Cc: Jann Horn <jannh@google.com>
Cc: Michael Kerrisk <mtk.manpages@gmail.com>
Cc: Aleksa Sarai <cyphar@cyphar.com>
Link: https://lore.kernel.org/r/20200505140432.181565-2-christian.brauner@ubuntu.com

diff --git a/fs/namespace.c b/fs/namespace.c
index a28e4db075ede216f684561fbc348a01670560a9..62899fad4a04046f33ae7cdd1479d81a4c554da1 100644 (file)
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -3954,16 +3954,18 @@ 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))
+           !ns_capable(user_ns, CAP_SYS_CHROOT) ||
+           !ns_capable(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 35942084cd40d56cc1bd9f7ccc08be460ad35cc9..007cfa52efb23093af98b55078f2c160faec17c2 100644 (file)
--- a/include/linux/mnt_namespace.h
+++ b/include/linux/mnt_namespace.h
@@ -6,6 +6,7 @@
 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 *);

diff --git a/include/linux/nsproxy.h b/include/linux/nsproxy.h
index 074f395b9ad25484871d2452325476253cb23932..cdb171efc7cb052dd4844ae182206939627c68e8 100644 (file)
--- 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 6abe85c346813a909552be811cd4573cac07c076..75807ecef880f1b12f690da75717e61600f50318 100644 (file)
--- 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 b3ca1476ca5118793c096a0244b062fbff7255b0..fdc3b5f3f53aa75796192460866c001f1571a2cc 100644 (file)
--- 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))
+           !ns_capable(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 b05f1dd58a6220c5c4231465bee3f461078f171e..812a61afd538a180d64b3ec35dbf3d978c7a059a 100644 (file)
--- a/kernel/cgroup/namespace.c
+++ b/kernel/cgroup/namespace.c
@@ -95,11 +95,12 @@ 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) ||
+       if (!ns_capable(nsset->cred->user_ns, CAP_SYS_ADMIN) ||
            !ns_capable(cgroup_ns->user_ns, CAP_SYS_ADMIN))
                return -EPERM;
 

diff --git a/kernel/nsproxy.c b/kernel/nsproxy.c
index ed9882108cd28f604e09f4a6e4f09137b3881076..b7954fd604753863d296e4063c2b8159a68c9e41 100644 (file)
--- 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 +258,79 @@ 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(int nstype, 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 (nstype == CLONE_NEWUSER)
+               nsset->cred = prepare_creds();
+       else
+               nsset->cred = current_cred();
+       if (!nsset->cred)
+               goto out;
+
+       if (nstype == CLONE_NEWNS)
+               nsset->fs = me->fs;
+
+       nsset->flags = nstype;
+       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;
+}
+
 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 +342,16 @@ 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(ns->ops->type, &nsset);
+       if (err)
                goto out;
-       }
 
-       err = ns->ops->install(new_nsproxy, ns);
-       if (err) {
-               free_nsproxy(new_nsproxy);
-               goto out;
+       err = ns->ops->install(&nsset, ns);
+       if (!err) {
+               commit_nsset(&nsset);
+               perf_event_namespaces(current);
        }
-       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 01f8ba32cc0c7fc8eade7a0f002d13b7e637bb00..11db2bdbb41e564dd77294d7a91c5eebe7be2c83 100644 (file)
--- 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))
+           !ns_capable(nsset->cred->user_ns, CAP_SYS_ADMIN))
                return -EPERM;
 
        /*

diff --git a/kernel/time/namespace.c b/kernel/time/namespace.c
index 53bce347cd50bc24b1fbebd8fc5c26cc97e6742a..5d9fc22d836a08009e613d617bd105bd2d9b0f61 100644 (file)
--- a/kernel/time/namespace.c
+++ b/kernel/time/namespace.c
@@ -280,8 +280,9 @@ 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;
 
@@ -289,7 +290,7 @@ static int timens_install(struct nsproxy *nsproxy, struct ns_common *new)
                return -EUSERS;
 
        if (!ns_capable(ns->user_ns, CAP_SYS_ADMIN) ||
-           !ns_capable(current_user_ns(), CAP_SYS_ADMIN))
+           !ns_capable(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 8eadadc478f9aa2c76693d9809b23726152650c2..87804e0371fe19b91a9e6e7d5092cd9814104531 100644 (file)
--- 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 f0e4911930092f6b82d1689ed1ed9ba79ab98a92..e488d0e2ab457b5f24c3c9c999cc49c7870b6839 100644 (file)
--- 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))
+           !ns_capable(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 190ca66a383b78bdf267e6a81a5270e7cb0a7710..dcd61aca343eca7247c127a18be840c2d1a79d34 100644 (file)
--- 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))
+           !ns_capable(nsset->cred->user_ns, CAP_SYS_ADMIN))
                return -EPERM;
 
        put_net(nsproxy->net_ns);