[Devel] Re: [PATCH 2/3] pidns: Call pid_ns_prepare_proc from create_pid_namespace

[Serge E. Hallyn]

Quoting Daniel Lezcano (daniel.lezcano at free.fr):
> From: Eric W. Biederman <ebiederm at xmission.com>
> 
> Reorganize proc_get_sb so it can be called before the struct pid
> of the first process is allocated.
> 
> Signed-off-by: Eric W. Biederman <ebiederm at xmission.com>
> Signed-off-by: Daniel Lezcano <daniel.lezcano at free.fr>

Acked-by: Serge E. Hallyn <serge at hallyn.com>

> ---
>  fs/proc/root.c         |   25 +++++++------------------
>  kernel/fork.c          |    6 ------
>  kernel/pid_namespace.c |   11 +++++++++--
>  3 files changed, 16 insertions(+), 26 deletions(-)
> 
> diff --git a/fs/proc/root.c b/fs/proc/root.c
> index ef9fa8e..e5e2bfa 100644
> --- a/fs/proc/root.c
> +++ b/fs/proc/root.c
> @@ -43,17 +43,6 @@ static struct dentry *proc_mount(struct file_system_type *fs_type,
>  	struct pid_namespace *ns;
>  	struct proc_inode *ei;
>  
> -	if (proc_mnt) {
> -		/* Seed the root directory with a pid so it doesn't need
> -		 * to be special in base.c.  I would do this earlier but
> -		 * the only task alive when /proc is mounted the first time
> -		 * is the init_task and it doesn't have any pids.
> -		 */
> -		ei = PROC_I(proc_mnt->mnt_sb->s_root->d_inode);
> -		if (!ei->pid)
> -			ei->pid = find_get_pid(1);
> -	}
> -
>  	if (flags & MS_KERNMOUNT)
>  		ns = (struct pid_namespace *)data;
>  	else
> @@ -71,16 +60,16 @@ static struct dentry *proc_mount(struct file_system_type *fs_type,
>  			return ERR_PTR(err);
>  		}
>  
> -		ei = PROC_I(sb->s_root->d_inode);
> -		if (!ei->pid) {
> -			rcu_read_lock();
> -			ei->pid = get_pid(find_pid_ns(1, ns));
> -			rcu_read_unlock();
> -		}
> -
>  		sb->s_flags |= MS_ACTIVE;
>  	}
>  
> +	ei = PROC_I(sb->s_root->d_inode);
> +	if (!ei->pid) {
> +		rcu_read_lock();
> +		ei->pid = get_pid(find_pid_ns(1, ns));
> +		rcu_read_unlock();
> +	}
> +
>  	return dget(sb->s_root);
>  }
>  
> diff --git a/kernel/fork.c b/kernel/fork.c
> index c9f0784..e7a5907 100644
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -1180,12 +1180,6 @@ static struct task_struct *copy_process(unsigned long clone_flags,
>  		pid = alloc_pid(p->nsproxy->pid_ns);
>  		if (!pid)
>  			goto bad_fork_cleanup_io;
> -
> -		if (clone_flags & CLONE_NEWPID) {
> -			retval = pid_ns_prepare_proc(p->nsproxy->pid_ns);
> -			if (retval < 0)
> -				goto bad_fork_free_pid;
> -		}
>  	}
>  
>  	p->pid = pid_nr(pid);
> diff --git a/kernel/pid_namespace.c b/kernel/pid_namespace.c
> index a5aff94..e9c9adc 100644
> --- a/kernel/pid_namespace.c
> +++ b/kernel/pid_namespace.c
> @@ -14,6 +14,7 @@
>  #include <linux/err.h>
>  #include <linux/acct.h>
>  #include <linux/slab.h>
> +#include <linux/proc_fs.h>
>  
>  #define BITS_PER_PAGE		(PAGE_SIZE*8)
>  
> @@ -72,7 +73,7 @@ static struct pid_namespace *create_pid_namespace(struct pid_namespace *parent_p
>  {
>  	struct pid_namespace *ns;
>  	unsigned int level = parent_pid_ns->level + 1;
> -	int i;
> +	int i, err = -ENOMEM;
>  
>  	ns = kmem_cache_zalloc(pid_ns_cachep, GFP_KERNEL);
>  	if (ns == NULL)
> @@ -96,14 +97,20 @@ static struct pid_namespace *create_pid_namespace(struct pid_namespace *parent_p
>  	for (i = 1; i < PIDMAP_ENTRIES; i++)
>  		atomic_set(&ns->pidmap[i].nr_free, BITS_PER_PAGE);
>  
> +	err = pid_ns_prepare_proc(ns);
> +	if (err)
> +		goto out_put_parent_pid_ns;
> +
>  	return ns;
>  
> +out_put_parent_pid_ns:
> +	put_pid_ns(parent_pid_ns);
>  out_free_map:
>  	kfree(ns->pidmap[0].page);
>  out_free:
>  	kmem_cache_free(pid_ns_cachep, ns);
>  out:
> -	return ERR_PTR(-ENOMEM);
> +	return ERR_PTR(err);
>  }
>  
>  static void destroy_pid_namespace(struct pid_namespace *ns)
> -- 
> 1.7.1
> 
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