[RFC PATCH v4 05/12] kmod - teach call_usermodehelper() to use a namespace

[Ian Kent]

From: Ian Kent <ikent@xxxxxxxxxx>

The call_usermodehelper() function executes all binaries in the
global "init" root context. This doesn't allow a binary to be run
within a namespace (eg. the namespaces of a container).

The init process of the callers environment is used to setup the
namespaces in almost the same way the root init process when the
UMH_USE_NS flag is used.

Signed-off-by: Ian Kent <ikent@xxxxxxxxxx>
Cc: Benjamin Coddington <bcodding@xxxxxxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: J. Bruce Fields <bfields@xxxxxxxxxxxx>
Cc: David Howells <dhowells@xxxxxxxxxx>
Cc: Trond Myklebust <trond.myklebust@xxxxxxxxxxxxxxx>
Cc: Oleg Nesterov <onestero@xxxxxxxxxx>
Cc: Eric W. Biederman <ebiederm@xxxxxxxxxxxx>
Cc: Jeff Layton <jeff.layton@xxxxxxxxxxxxxxx>
---
 kernel/kmod.c |   66 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 66 insertions(+)

diff --git a/kernel/kmod.c b/kernel/kmod.c
index 213dbe0..d6ee21a 100644
--- a/kernel/kmod.c
+++ b/kernel/kmod.c
@@ -56,6 +56,8 @@ static kernel_cap_t usermodehelper_inheritable = CAP_FULL_SET;
 static DEFINE_SPINLOCK(umh_sysctl_lock);
 static DECLARE_RWSEM(umhelper_sem);
 
+static void umh_put_nsproxy(struct subprocess_info *);
+
 #ifdef CONFIG_MODULES
 
 /*
@@ -194,6 +196,7 @@ static void call_usermodehelper_freeinfo(struct subprocess_info *info)
 {
 	if (info->cleanup)
 		(*info->cleanup)(info);
+	umh_put_nsproxy(info);
 	kfree(info);
 }
 
@@ -565,6 +568,61 @@ static void helper_unlock(void)
 		wake_up(&running_helpers_waitq);
 }
 
+#ifndef CONFIG_NAMESPACES
+static int umh_get_nsproxy(struct subprocess_info *sub_info)
+{
+	return -ENOTSUP;
+}
+
+static void umh_put_nsproxy(struct subprocess_info *sub_info)
+{
+}
+#else
+static int umh_get_nsproxy(struct subprocess_info *sub_info)
+{
+	struct umh_ns_info *nsinfo = &sub_info->nsinfo;
+	struct task_struct *tsk;
+	struct user_namespace *user_ns;
+	struct nsproxy *new;
+	int err = 0;
+
+	rcu_read_lock();
+	tsk = find_task_by_vpid(1);
+	if (tsk)
+		get_task_struct(tsk);
+	rcu_read_unlock();
+	if (!tsk) {
+		err = -ESRCH;
+		goto out;
+	}
+
+	user_ns = get_user_ns(tsk->cred->user_ns);
+
+	new = create_new_namespaces(0, tsk, user_ns, tsk->fs);
+	if (IS_ERR(new)) {
+		err = PTR_ERR(new);
+		put_user_ns(user_ns);
+		put_task_struct(tsk);
+		goto out;
+	}
+
+	put_task_struct(tsk);
+
+	nsinfo->nsproxy = new;
+	nsinfo->user_ns = user_ns;
+out:
+	return err;
+}
+
+static void umh_put_nsproxy(struct subprocess_info *sub_info)
+{
+	if (sub_info->nsinfo.nsproxy) {
+		put_nsproxy(sub_info->nsinfo.nsproxy);
+		put_user_ns(sub_info->nsinfo.user_ns);
+	}
+}
+#endif
+
 /**
  * call_usermodehelper_setup - prepare to call a usermode helper
  * @path: path to usermode executable
@@ -697,6 +755,14 @@ int call_usermodehelper(char *path,
 	if (info == NULL)
 		return -ENOMEM;
 
+	if (flags & UMH_USE_NS) {
+		int err = umh_get_nsproxy(info);
+		if (err) {
+			kfree(info);
+			return err;
+		}
+	}
+
 	return call_usermodehelper_exec(info, flags);
 }
 EXPORT_SYMBOL(call_usermodehelper);

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