[PATCH review 10/16] userns: Implement unshare of the user namespace

Eric W. Biederman
2012-11-19T15:13:33Z

- Add CLONE_THREAD to the unshare flags if CLONE_NEWUSER is selected
As changing user namespaces is only valid if all there is only
a single thread.
- Restore the code to add CLONE_VM if CLONE_THREAD is selected and
the code to addCLONE_SIGHAND if CLONE_VM is selected.
Making the constraints in the code clear.

Acked-by: Serge Hallyn <serge.hallyn@canonical.com>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
---
include/linux/nsproxy.h | 2 +-
include/linux/user_namespace.h | 9 +++++++++
kernel/fork.c | 25 ++++++++++++++++++++++---
kernel/nsproxy.c | 8 ++++----
kernel/user_namespace.c | 15 +++++++++++++++
5 files changed, 51 insertions(+), 8 deletions(-)

diff --git a/include/linux/nsproxy.h b/include/linux/nsproxy.h
index cc37a55..10e5947 100644
--- a/include/linux/nsproxy.h
+++ b/include/linux/nsproxy.h
@@ -67,7 +67,7 @@ void exit_task_namespaces(struct task_struct *tsk);
void switch_task_namespaces(struct task_struct *tsk, struct nsproxy *new);
void free_nsproxy(struct nsproxy *ns);
int unshare_nsproxy_namespaces(unsigned long, struct nsproxy **,
- struct fs_struct *);
+ struct cred *, struct fs_struct *);
int __init nsproxy_cache_init(void);

static inline void put_nsproxy(struct nsproxy *ns)
diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h
index 95142ca..17651f0 100644
--- a/include/linux/user_namespace.h
+++ b/include/linux/user_namespace.h
@@ -39,6 +39,7 @@ static inline struct user_namespace *get_user_ns(struct user_namespace *ns)
}

extern int create_user_ns(struct cred *new);
+extern int unshare_userns(unsigned long unshare_flags, struct cred **new_cred);
extern void free_user_ns(struct kref *kref);

static inline void put_user_ns(struct user_namespace *ns)
@@ -66,6 +67,14 @@ static inline int create_user_ns(struct cred *new)
return -EINVAL;
}

+static inline int unshare_userns(unsigned long unshare_flags,
+ struct cred **new_cred)
+{
+ if (unshare_flags & CLONE_NEWUSER)
+ return -EINVAL;
+ return 0;
+}
+
static inline void put_user_ns(struct user_namespace *ns)
{
}
diff --git a/kernel/fork.c b/kernel/fork.c
index 8c29abb..38e53b8 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1687,7 +1687,7 @@ static int check_unshare_flags(unsigned long unshare_flags)
if (unshare_flags & ~(CLONE_THREAD|CLONE_FS|CLONE_NEWNS|CLONE_SIGHAND|
CLONE_VM|CLONE_FILES|CLONE_SYSVSEM|
CLONE_NEWUTS|CLONE_NEWIPC|CLONE_NEWNET|
- CLONE_NEWPID))
+ CLONE_NEWUSER|CLONE_NEWPID))
return -EINVAL;
/*
* Not implemented, but pretend it works if there is nothing to
@@ -1754,11 +1754,17 @@ SYSCALL_DEFINE1(unshare, unsigned long, unshare_flags)
{
struct fs_struct *fs, *new_fs = NULL;
struct files_struct *fd, *new_fd = NULL;
+ struct cred *new_cred = NULL;
struct nsproxy *new_nsproxy = NULL;
int do_sysvsem = 0;
int err;

/*
+ * If unsharing a user namespace must also unshare the thread.
+ */
+ if (unshare_flags & CLONE_NEWUSER)
+ unshare_flags |= CLONE_THREAD;
+ /*
* If unsharing a pid namespace must also unshare the thread.
*/
if (unshare_flags & CLONE_NEWPID)
@@ -1795,11 +1801,15 @@ SYSCALL_DEFINE1(unshare, unsigned long, unshare_flags)
err = unshare_fd(unshare_flags, &new_fd);
if (err)
goto bad_unshare_cleanup_fs;
- err = unshare_nsproxy_namespaces(unshare_flags, &new_nsproxy, new_fs);
+ err = unshare_userns(unshare_flags, &new_cred);
if (err)
goto bad_unshare_cleanup_fd;
+ err = unshare_nsproxy_namespaces(unshare_flags, &new_nsproxy,
+ new_cred, new_fs);
+ if (err)
+ goto bad_unshare_cleanup_cred;

- if (new_fs || new_fd || do_sysvsem || new_nsproxy) {
+ if (new_fs || new_fd || do_sysvsem || new_cred || new_nsproxy) {
if (do_sysvsem) {
/*
* CLONE_SYSVSEM is equivalent to sys_exit().
@@ -1832,11 +1842,20 @@ SYSCALL_DEFINE1(unshare, unsigned long, unshare_flags)
}

task_unlock(current);
+
+ if (new_cred) {
+ /* Install the new user namespace */
+ commit_creds(new_cred);
+ new_cred = NULL;
+ }
}

if (new_nsproxy)
put_nsproxy(new_nsproxy);

+bad_unshare_cleanup_cred:
+ if (new_cred)
+ put_cred(new_cred);
bad_unshare_cleanup_fd:
if (new_fd)
put_files_struct(new_fd);
diff --git a/kernel/nsproxy.c b/kernel/nsproxy.c
index 2ddd816..78e2ecb 100644
--- a/kernel/nsproxy.c
+++ b/kernel/nsproxy.c
@@ -186,7 +186,7 @@ void free_nsproxy(struct nsproxy *ns)
* On success, returns the new nsproxy.
*/
int unshare_nsproxy_namespaces(unsigned long unshare_flags,
- struct nsproxy **new_nsp, struct fs_struct *new_fs)
+ struct nsproxy **new_nsp, struct cred *new_cred, struct fs_struct *new_fs)
{
struct user_namespace *user_ns;
int err = 0;
@@ -195,12 +195,12 @@ int unshare_nsproxy_namespaces(unsigned long unshare_flags,
CLONE_NEWNET | CLONE_NEWPID)))
return 0;

- if (!nsown_capable(CAP_SYS_ADMIN))
+ user_ns = new_cred ? new_cred->user_ns : current_user_ns();
+ if (!ns_capable(user_ns, CAP_SYS_ADMIN))
return -EPERM;

- user_ns = current_user_ns();
*new_nsp = create_new_namespaces(unshare_flags, current, user_ns,
- new_fs ? new_fs : current->fs);
+ new_fs ? new_fs : current->fs);
if (IS_ERR(*new_nsp)) {
err = PTR_ERR(*new_nsp);
goto out;
diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
index a946077..ce92f7e 100644
--- a/kernel/user_namespace.c
+++ b/kernel/user_namespace.c
@@ -82,6 +82,21 @@ int create_user_ns(struct cred *new)
return 0;
}

+int unshare_userns(unsigned long unshare_flags, struct cred **new_cred)
+{
+ struct cred *cred;
+
+ if (!(unshare_flags & CLONE_NEWUSER))
+ return 0;
+
+ cred = prepare_creds();
+ if (!cred)
+ return -ENOMEM;
+
+ *new_cred = cred;
+ return create_user_ns(cred);
+}
+
void free_user_ns(struct kref *kref)
{
struct user_namespace *parent, *ns =
--
1.7.5.4