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

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

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@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>
---
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);