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Message-ID: <20150206070859.7eb499b0@tlielax.poochiereds.net>
Date: Fri, 6 Feb 2015 07:08:59 -0500
From: Jeff Layton <jeff.layton@...marydata.com>
To: Ian Kent <ikent@...hat.com>
Cc: Kernel Mailing List <linux-kernel@...r.kernel.org>,
David Howells <dhowells@...hat.com>,
Oleg Nesterov <onestero@...hat.com>,
Trond Myklebust <trond.myklebust@...marydata.com>,
"J. Bruce Fields" <bfields@...ldses.org>,
Benjamin Coddington <bcodding@...hat.com>,
Al Viro <viro@...IV.linux.org.uk>,
"Eric W. Biederman" <ebiederm@...ssion.com>
Subject: Re: [RFC PATCH 3/8] kmod - teach call_usermodehelper() to use a
namespace
On Thu, 05 Feb 2015 10:34:11 +0800
Ian Kent <ikent@...hat.com> wrote:
> 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 namespace of a container).
>
> Both containerized NFS client and NFS server need the ability to
> execute a binary in a container's context. To do this use the init
> process of the callers environment is used to setup the namespaces
> in the same way the root init process is used otherwise.
>
> Signed-off-by: Ian Kent <ikent@...hat.com>
> Cc: Benjamin Coddington <bcodding@...hat.com>
> Cc: Al Viro <viro@...IV.linux.org.uk>
> Cc: J. Bruce Fields <bfields@...ldses.org>
> Cc: David Howells <dhowells@...hat.com>
> Cc: Trond Myklebust <trond.myklebust@...marydata.com>
> Cc: Oleg Nesterov <onestero@...hat.com>
> Cc: Eric W. Biederman <ebiederm@...ssion.com>
> Cc: Jeff Layton <jeff.layton@...marydata.com>
> ---
> include/linux/kmod.h | 16 +++++++
> kernel/kmod.c | 115 +++++++++++++++++++++++++++++++++++++++++++++++++-
> 2 files changed, 128 insertions(+), 3 deletions(-)
>
> diff --git a/include/linux/kmod.h b/include/linux/kmod.h
> index 15bdeed..b0f1b3c 100644
> --- a/include/linux/kmod.h
> +++ b/include/linux/kmod.h
> @@ -52,6 +52,7 @@ 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 8 /* exec using caller's init namespace */
>
> struct subprocess_info {
> struct work_struct work;
> @@ -69,6 +70,21 @@ struct subprocess_info {
> extern int
> call_usermodehelper(char *path, char **argv, char **envp, int flags);
>
> +#if !defined(CONFIG_PROC_FS) || !defined(CONFIG_NAMESPACES)
> +inline struct task_struct *umh_get_init_task(void)
> +{
> + return ERR_PTR(-ENOTSUP);
> +}
> +
> +inline int umh_enter_ns(struct task_struct *tsk, struct cred *new)
> +{
> + return -ENOTSUP;
> +}
> +#else
> +struct task_struct *umh_get_init_pid(void);
> +int umh_enter_ns(struct task_struct *tsk, struct cred *new);
> +#endif
> +
> extern struct subprocess_info *
> call_usermodehelper_setup(char *path, char **argv, char **envp, gfp_t gfp_mask,
> int (*init)(struct subprocess_info *info, struct cred *new),
> diff --git a/kernel/kmod.c b/kernel/kmod.c
> index 14c0188..4c649d6 100644
> --- a/kernel/kmod.c
> +++ b/kernel/kmod.c
> @@ -582,6 +582,98 @@ unlock:
> }
> EXPORT_SYMBOL(call_usermodehelper_exec);
>
> +#if defined(CONFIG_PROC_FS) && defined(CONFIG_NAMESPACES)
> +#define NS_PATH_MAX 35
> +#define NS_PATH_FMT "%lu/ns/%s"
> +
> +/* Note namespace name order is significant */
> +static const char *ns_names[] = { "user", "ipc", "uts", "net", "pid", "mnt", NULL };
> +
> +struct task_struct *umh_get_init_pid(void)
nit: we're not getting a pid here but a task_struct pointer. Maybe this
should be called umh_get_init_task?
> +{
> + struct task_struct *tsk;
> +
> + rcu_read_lock();
> + tsk = find_task_by_vpid(1);
> + if (tsk)
> + get_task_struct(tsk);
> + rcu_read_unlock();
I'm not terribly familiar with the task_struct lifetime rules...
I assume that you can be assured that tsk won't go away while you hold
the rcu_read_lock, but is doing a get_task_struct while holding it
sufficient to pin it after you drop the lock?
IOW, could the refcount on the task_struct do a 0->1 transition here and
end up being freed anyway after you've grabbed a reference?
> + if (!tsk)
> + return ERR_PTR(-ESRCH);
> +
> + return tsk;
> +}
> +EXPORT_SYMBOL(umh_get_init_pid);
> +
> +int umh_enter_ns(struct task_struct *tsk, struct cred *new)
> +{
> + char path[NS_PATH_MAX];
> + struct vfsmount *mnt;
> + const char *name;
> + pid_t pid;
> + int err = 0;
> +
> + pid = task_pid_nr(tsk);
> +
> + /*
> + * The user mode thread runner runs in the root init namespace
> + * so it will see all system pids.
> + */
> + mnt = task_active_pid_ns(current)->proc_mnt;
> +
> + for (name = ns_names[0]; *name; name++) {
> + struct file *this;
> + int len;
> +
> + len = snprintf(path,
> + NS_PATH_MAX, NS_PATH_FMT,
> + (unsigned long) pid, name);
> + if (len >= NS_PATH_MAX) {
> + err = -ENAMETOOLONG;
> + break;
> + }
> +
> + this = file_open_root(mnt->mnt_root, mnt, path, O_RDONLY);
> + if (unlikely(IS_ERR(this))) {
> + err = PTR_ERR(this);
> + break;
> + }
> +
> + err = setns_inode(file_inode(this), 0);
> + fput(this);
> + if (err)
> + break;
> + }
> +
> + return err;
> +}
> +EXPORT_SYMBOL(umh_enter_ns);
> +
> +static int umh_set_ns(struct subprocess_info *info, struct cred *new)
> +{
> + struct task_struct *tsk = info->data;
> +
> + return umh_enter_ns(tsk, new);
> +}
> +
> +static void umh_free_ns(struct subprocess_info *info)
> +{
> + struct task_struct *tsk = info->data;
> +
> + if (tsk)
> + put_task_struct(tsk);
> +}
> +#else
> +static int umh_set_ns(struct subprocess_info *info, struct cred *new)
> +{
> + return 0;
> +}
> +
> +static void umh_free_ns(struct subprocess_info *info)
> +{
> +}
> +#endif
> +
> /**
> * call_usermodehelper() - prepare and start a usermode application
> * @path: path to usermode executable
> @@ -599,11 +691,28 @@ int call_usermodehelper(char *path, char **argv, char **envp, int flags)
> {
> struct subprocess_info *info;
> gfp_t gfp_mask = (flags == UMH_NO_WAIT) ? GFP_ATOMIC : GFP_KERNEL;
> + unsigned int use_ns = flags & UMH_USE_NS;
> + struct task_struct *tsk = NULL;
> +
> + if (use_ns) {
> + tsk = umh_get_init_pid();
> + if (IS_ERR(tsk))
> + return PTR_ERR(tsk);
> + }
>
> - info = call_usermodehelper_setup(path, argv, envp, gfp_mask,
> - NULL, NULL, NULL);
> - if (info == NULL)
> + if (!tsk)
> + info = call_usermodehelper_setup(path, argv, envp,
> + gfp_mask, NULL, NULL, NULL);
> + else {
> + info = call_usermodehelper_setup(path, argv, envp, gfp_mask,
> + umh_set_ns, umh_free_ns,
> + tsk);
> + }
> + if (info == NULL) {
> + if (tsk)
> + put_task_struct(tsk);
> return -ENOMEM;
> + }
>
> return call_usermodehelper_exec(info, flags);
> }
>
--
Jeff Layton <jeff.layton@...marydata.com>
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