[RFC PATCH v4 04/12] kmod - add namespace aware thread runner

Ian Kent
2015-03-17T02:45:41Z

Make usermode helper thread runner namespace aware.

Signed-off-by: Ian Kent <ikent@redhat.com>
Cc: Benjamin Coddington <bcodding@redhat.com>
Cc: Al Viro <viro@ZenIV.linux.org.uk>
Cc: J. Bruce Fields <bfields@fieldses.org>
Cc: David Howells <dhowells@redhat.com>
Cc: Trond Myklebust <trond.myklebust@primarydata.com>
Cc: Oleg Nesterov <onestero@redhat.com>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Cc: Jeff Layton <jeff.layton@primarydata.com>
---
include/linux/kmod.h | 12 ++++++
kernel/kmod.c | 98 ++++++++++++++++++++++++++++++++++++++++++++++++--
2 files changed, 106 insertions(+), 4 deletions(-)

diff --git a/include/linux/kmod.h b/include/linux/kmod.h
index e647ddb..64c81c9 100644
--- a/include/linux/kmod.h
+++ b/include/linux/kmod.h
@@ -25,6 +25,7 @@
#include <linux/compiler.h>
#include <linux/workqueue.h>
#include <linux/sysctl.h>
+#include <linux/user_namespace.h>

#define KMOD_PATH_LEN 256

@@ -52,6 +53,14 @@ struct file;
#define UMH_WAIT_EXEC 1 /* wait for the exec, but not the process */
#define UMH_WAIT_PROC 2 /* wait for the process to complete */
#define UMH_KILLABLE 4 /* wait for EXEC/PROC killable */
+#define UMH_USE_NS 32 /* exec using caller's init namespace */
+
+#ifdef CONFIG_NAMESPACES
+struct umh_ns_info {
+ struct nsproxy *nsproxy;
+ struct user_namespace *user_ns;
+};
+#endif

struct subprocess_info {
struct work_struct work;
@@ -64,6 +73,9 @@ struct subprocess_info {
int (*init)(struct subprocess_info *info, struct cred *new);
void (*cleanup)(struct subprocess_info *info);
void *data;
+#ifdef CONFIG_NAMESPACES
+ struct umh_ns_info nsinfo;
+#endif
};

extern int
diff --git a/kernel/kmod.c b/kernel/kmod.c
index e968e2d..213dbe0 100644
--- a/kernel/kmod.c
+++ b/kernel/kmod.c
@@ -39,6 +39,7 @@
#include <linux/rwsem.h>
#include <linux/ptrace.h>
#include <linux/async.h>
+#include <linux/proc_ns.h>
#include <asm/uaccess.h>

#include <trace/events/module.h>
@@ -303,11 +304,8 @@ static int wait_for_helper(void *data)
do_exit(0);
}

-/* This is run by khelper thread */
-static void __call_usermodehelper(struct work_struct *work)
+static pid_t umh_kernel_thread(struct subprocess_info *sub_info)
{
- struct subprocess_info *sub_info =
- container_of(work, struct subprocess_info, work);
pid_t pid;

if (sub_info->flags & UMH_WAIT_PROC)
@@ -316,7 +314,99 @@ static void __call_usermodehelper(struct work_struct *work)
else
pid = kernel_thread(____call_usermodehelper, sub_info,
SIGCHLD);
+ return pid;
+}
+
+#ifndef CONFIG_NAMESPACES
+static pid_t umh_kernel_thread_in_ns(struct subprocess_info *sub_info)
+{
+ return -ENOTSUP;
+}
+#else
+static pid_t umh_kernel_thread_in_ns(struct subprocess_info *sub_info)
+{
+ struct umh_ns_info *info = &sub_info->nsinfo;
+ struct nsproxy *saved_nsp, *new_nsp;
+ struct user_namespace *user_ns;
+ struct pid_namespace *pid_ns;
+ struct mnt_namespace *mnt_ns;
+ pid_t pid;
+ int err;
+
+ saved_nsp = current->nsproxy;
+ get_nsproxy(saved_nsp);
+
+ new_nsp = info->nsproxy;
+ get_nsproxy(new_nsp);
+
+ user_ns = get_user_ns(current->cred->user_ns);
+ if (info->user_ns) {
+ err = user_ns->ns.ops->install(new_nsp, &info->user_ns->ns);
+ if (err)
+ goto out;
+ }
+
+ /* May need to wait4() completion so a pid valid in the
+ * thread runners namespace is needed. Install current
+ * pid ns in the nsproxy.
+ */
+ pid_ns = current->nsproxy->pid_ns_for_children;
+ if (pid_ns) {
+ err = pid_ns->ns.ops->install(new_nsp, &pid_ns->ns);
+ if (err)
+ goto out_user_ns;
+ }
+
+ /* The mount namespace install function is a little
+ * more than a no-op, as the install functions of the
+ * other namespace types are in our case, we need to
+ * call it to setup current fs root and pwd.
+ */
+ mnt_ns = current->nsproxy->mnt_ns;
+ err = mnt_ns->ns.ops->install(new_nsp, &new_nsp->mnt_ns->ns);
+ if (err)
+ goto out_user_ns;

+ /* Finally, switch to the nsproxy of the init namespace
+ * of the caller.
+ */
+ switch_task_namespaces(current, new_nsp);
+
+ pid = umh_kernel_thread(sub_info);
+
+ mnt_ns->ns.ops->install(saved_nsp, &saved_nsp->mnt_ns->ns);
+
+ if (info->user_ns)
+ user_ns->ns.ops->install(saved_nsp, &user_ns->ns);
+
+ switch_task_namespaces(current, saved_nsp);
+
+ put_user_ns(user_ns);
+
+ return pid;
+
+out_user_ns:
+ if (info->user_ns)
+ user_ns->ns.ops->install(saved_nsp, &user_ns->ns);
+out:
+ put_user_ns(user_ns);
+ put_nsproxy(new_nsp);
+ put_nsproxy(saved_nsp);
+ return err;
+}
+#endif
+
+/* This is run by khelper thread */
+static void __call_usermodehelper(struct work_struct *work)
+{
+ struct subprocess_info *sub_info =
+ container_of(work, struct subprocess_info, work);
+ pid_t pid;
+
+ if (sub_info->flags & UMH_USE_NS)
+ pid = umh_kernel_thread_in_ns(sub_info);
+ else
+ pid = umh_kernel_thread(sub_info);
if (pid < 0) {
sub_info->retval = pid;
umh_complete(sub_info);