[Devel] Re: [RFC][PATCH 6/6]: Enable unsharing pid namespace.

[Eric W. Biederman]

sukadev at us.ibm.com writes:

> From: Cedric Le Goater <clg at fr.ibm.com>
> Subject: [RFC][PATCH 6/6]: Enable unsharing pid namespace.
>
> Enable unsharing of pid namespace - i.e allow creating and using
> a new pid namespace and attaching multiple struct pid_nrs per
> process, one for each namespace.
>
> Signed-off-by: Cedric Le Goater <clg at fr.ibm.com>
> Signed-off-by: Sukadev Bhattiprolu <sukadev at us.ibm.com>
>
> ---
>  include/linux/sched.h |    1 +
>  kernel/fork.c         |   22 ++++++++++++++++++----
>  kernel/nsproxy.c      |    5 ++++-
>  kernel/pid.c          |   18 ++++++++++++++++++
>  4 files changed, 41 insertions(+), 5 deletions(-)
>
> Index: lx26-20-mm2b/kernel/pid.c
> ===================================================================
> --- lx26-20-mm2b.orig/kernel/pid.c	2007-03-09 14:56:53.000000000 -0800
> +++ lx26-20-mm2b/kernel/pid.c	2007-03-09 15:03:05.000000000 -0800
> @@ -546,6 +546,24 @@ void free_pid_ns(struct kref *kref)
>  	struct pid_namespace *ns;
>  
>  	ns = container_of(kref, struct pid_namespace, kref);
> +
> +	if (ns != &init_pid_ns) {

A cleaned up version of this would make sense.
We don't need to test that ns != init_pid_ns.  
Maybe BUG_ON(ns == &init_pid_ns);

Or do you foresee freeing the initial pid namespace?


> +		/* BEGIN: to be removed soon */
> +		int i;
> +		int nr_free = atomic_read(&ns->pidmap[0].nr_free);
> +
> +		BUG_ON( nr_free != (BITS_PER_PAGE - 1));
> +
> +		if (unlikely(PIDMAP_ENTRIES != 1)) {
> +			for (i = 1; i < PIDMAP_ENTRIES; i++) {
> +				nr_free = atomic_read(&ns->pidmap[i].nr_free);
> +				BUG_ON(nr_free != BITS_PER_PAGE);
> +			}
> +		}
What makes the first page in the pidmap special?  None of the pages should have
an allocated bit if we are freeing the pid namespace....

> +		/* END: to be removed soon */
> +		kfree(ns->pidmap[0].page);

This is wrong.  While a pid namespace is exists we don't free the page
so you need to loop through all of the pidmap entries and free them.


> +	}
> +
>  	kfree(ns);
>  }
>  
> Index: lx26-20-mm2b/include/linux/sched.h
> ===================================================================
> --- lx26-20-mm2b.orig/include/linux/sched.h 2007-03-09 14:56:12.000000000 -0800
> +++ lx26-20-mm2b/include/linux/sched.h	2007-03-09 14:56:53.000000000 -0800
> @@ -26,6 +26,7 @@
>  #define CLONE_STOPPED		0x02000000	/* Start in stopped state */
>  #define CLONE_NEWUTS		0x04000000	/* New utsname group? */
>  #define CLONE_NEWIPC		0x08000000	/* New ipcs */
> +#define CLONE_NEWPID		0x10000000	/* New pid namespace */

Good.  Although it may make sense to submit this as a separate patch.  We
should be able to reserve the number now.

> Index: lx26-20-mm2b/kernel/fork.c
> ===================================================================
> --- lx26-20-mm2b.orig/kernel/fork.c	2007-03-09 14:56:12.000000000 -0800
> +++ lx26-20-mm2b/kernel/fork.c	2007-03-09 15:05:39.000000000 -0800
> @@ -57,6 +57,7 @@
>  #include <asm/mmu_context.h>
>  #include <asm/cacheflush.h>
>  #include <asm/tlbflush.h>
> +#include <linux/pid_namespace.h>

I don't see do_fork support only unshare support which seems completely
backwards to me.

> @@ -1609,6 +1610,7 @@ asmlinkage long sys_unshare(unsigned lon
>  	struct nsproxy *new_nsproxy = NULL, *old_nsproxy = NULL;
>  	struct uts_namespace *uts, *new_uts = NULL;
>  	struct ipc_namespace *ipc, *new_ipc = NULL;
> +	struct pid_nr *new_pid_nr = NULL;
>  
>  	check_unshare_flags(&unshare_flags);
>  
> @@ -1616,7 +1618,7 @@ asmlinkage long sys_unshare(unsigned lon
>  	err = -EINVAL;
>  	if (unshare_flags & ~(CLONE_THREAD|CLONE_FS|CLONE_NEWNS|CLONE_SIGHAND|
>  				CLONE_VM|CLONE_FILES|CLONE_SYSVSEM|
> -				CLONE_NEWUTS|CLONE_NEWIPC))
> +				CLONE_NEWUTS|CLONE_NEWIPC|CLONE_NEWPID))
>  		goto bad_unshare_out;
>  
>  	if ((err = unshare_thread(unshare_flags)))
> @@ -1637,18 +1639,20 @@ asmlinkage long sys_unshare(unsigned lon
>  		goto bad_unshare_cleanup_semundo;
>  	if ((err = unshare_ipcs(unshare_flags, &new_ipc)))
>  		goto bad_unshare_cleanup_uts;
> +	if ((err = unshare_pid_ns(unshare_flags, &new_pid_nr)))
> +		goto bad_unshare_cleanup_ipc;
>  
> -	if (new_ns || new_uts || new_ipc) {
> +	if (new_ns || new_uts || new_ipc || new_pid_nr) {
>  		old_nsproxy = current->nsproxy;
>  		new_nsproxy = dup_namespaces(old_nsproxy);
>  		if (!new_nsproxy) {
>  			err = -ENOMEM;
> -			goto bad_unshare_cleanup_ipc;
> +			goto bad_unshare_cleanup_pid;
>  		}
>  	}
>  
>  	if (new_fs || new_ns || new_mm || new_fd || new_ulist ||
> -				new_uts || new_ipc) {
> +				new_uts || new_ipc || new_pid_nr) {
>  
>  		task_lock(current);
>  
> @@ -1696,12 +1700,22 @@ asmlinkage long sys_unshare(unsigned lon
>  			new_ipc = ipc;
>  		}
>  
> +		if (new_pid_nr) {
> +			pid = task_pid_ns(current);
> +			set_task_pid_ns(current, new_pid_nr->pid_ns);
> +			new_pid_nr = NULL;
> +		}
> +
>  		task_unlock(current);
>  	}
>  
>  	if (new_nsproxy)
>  		put_nsproxy(new_nsproxy);
>  
> +bad_unshare_cleanup_pid:
> +	if (new_pid_nr)
> +		free_pidmap_pid_nr(new_pid_nr);
> +
>  bad_unshare_cleanup_ipc:
>  	if (new_ipc)
>  		put_ipc_ns(new_ipc);
> Index: lx26-20-mm2b/kernel/nsproxy.c
> ===================================================================
> --- lx26-20-mm2b.orig/kernel/nsproxy.c	2007-03-09 14:56:12.000000000 -0800
> +++ lx26-20-mm2b/kernel/nsproxy.c	2007-03-09 15:03:05.000000000 -0800
> @@ -83,13 +83,16 @@ int copy_namespaces(int flags, struct ta
>  	struct nsproxy *old_ns = tsk->nsproxy;
>  	struct nsproxy *new_ns;
>  	int err = 0;
> +	int ns_all;
>  
>  	if (!old_ns)
>  		return 0;
>  
>  	get_nsproxy(old_ns);
>  
> -	if (!(flags & (CLONE_NEWNS | CLONE_NEWUTS | CLONE_NEWIPC)))
> +	ns_all = CLONE_NEWNS | CLONE_NEWUTS | CLONE_NEWIPC | CLONE_NEWPID;
> +

This doesn't quite seem to make sense why the extra intermediate variable?

> +	if (!(flags & ns_all))
>  		return 0;
>  

Eric
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