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SubjectRe: [PATCH 2/7] ns: Introduce the setns syscall
On Fri, May 06, 2011 at 07:24:56PM -0700, Eric W. Biederman wrote:
> With the networking stack today there is demand to handle
> multiple network stacks at a time. Not in the context
> of containers but in the context of people doing interesting
> things with routing.
>
> There is also demand in the context of containers to have
> an efficient way to execute some code in the container itself.
> If nothing else it is very useful ad a debugging technique.
>
> Both problems can be solved by starting some form of login
> daemon in the namespaces people want access to, or you
> can play games by ptracing a process and getting the
> traced process to do things you want it to do. However
> it turns out that a login daemon or a ptrace puppet
> controller are more code, they are more prone to
> failure, and generally they are less efficient than
> simply changing the namespace of a process to a
> specified one.
>
> Pieces of this puzzle can also be solved by instead of
> coming up with a general purpose system call coming up
> with targed system calls perhaps socketat that solve
> a subset of the larger problem. Overall that appears
> to be more work for less reward.
>
> int setns(int fd, int nstype);
>
> The fd argument is a file descriptor referring to a proc
> file of the namespace you want to switch the process to.
>
> In the setns system call the nstype is 0 or specifies
> an clone flag of the namespace you intend to change
> to prevent changing a namespace unintentionally.
>
> v2: Most of the architecture support added by Daniel Lezcano <dlezcano@fr.ibm.com>
> v3: ported to v2.6.36-rc4 by: Eric W. Biederman <ebiederm@xmission.com>
> v4: Moved wiring up of the system call to another patch
>
> Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
> ---
> kernel/nsproxy.c | 37 +++++++++++++++++++++++++++++++++++++
> 1 files changed, 37 insertions(+), 0 deletions(-)
>
> diff --git a/kernel/nsproxy.c b/kernel/nsproxy.c
> index a05d191..96059d8 100644
> --- a/kernel/nsproxy.c
> +++ b/kernel/nsproxy.c
> @@ -22,6 +22,9 @@
> #include <linux/pid_namespace.h>
> #include <net/net_namespace.h>
> #include <linux/ipc_namespace.h>
> +#include <linux/proc_fs.h>
> +#include <linux/file.h>
> +#include <linux/syscalls.h>
>
> static struct kmem_cache *nsproxy_cachep;
>
> @@ -233,6 +236,40 @@ void exit_task_namespaces(struct task_struct *p)
> switch_task_namespaces(p, NULL);
> }
>
> +SYSCALL_DEFINE2(setns, int, fd, int, nstype)
> +{
> + const struct proc_ns_operations *ops;
> + struct task_struct *tsk = current;
> + struct nsproxy *new_nsproxy;
> + struct proc_inode *ei;
> + struct file *file;
> + int err;
> +
> + if (!capable(CAP_SYS_ADMIN))
> + return -EPERM;
> +
> + file = proc_ns_fget(fd);
> + if (IS_ERR(file))
> + return PTR_ERR(file);
> +
> + err = -EINVAL;
> + ei = PROC_I(file->f_dentry->d_inode);
> + ops = ei->ns_ops;
> + if (nstype && (ops->type != nstype))
> + goto out;
> +
> + new_nsproxy = create_new_namespaces(0, tsk, tsk->fs);

Doesn't this need some error checking like:

if (IS_ERR(new_nsproxy)) {
err = PTR_ERR(new_nsproxy);
goto out;
}

> + err = ops->install(new_nsproxy, ei->ns);
> + if (err) {
> + free_nsproxy(new_nsproxy);
> + goto out;
> + }
> + switch_task_namespaces(tsk, new_nsproxy);
> +out:
> + fput(file);
> + return err;
> +}
> +
> static int __init nsproxy_cache_init(void)
> {
> nsproxy_cachep = KMEM_CACHE(nsproxy, SLAB_PANIC);
> --
> 1.6.5.2.143.g8cc62
>
> _______________________________________________
> Containers mailing list
> Containers@lists.linux-foundation.org
> https://lists.linux-foundation.org/mailman/listinfo/containers


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