[Devel] Re: [PATCH] ipc: Save the ipc namespace while reading proc files.

[Serge E. Hallyn]

Quoting Eric W. Biederman (ebiederm at xmission.com):
> 
> The problem we were assuming that current->nsproxy->ipc_ns would never
> change while someone has our file in /proc/sysvipc/ file open.  Given
> that this can change with both unshare and by passing the file
> descriptor to another process that assumption is occasionally wrong. 
> 
> Therefore this patch causes /proc/sysvipc/* to cache the namespace
> and increment it's count when we open the file and to decrement the
> count when we close the file, ensuring consistent operation with
> no surprises.

Looks good, thanks.

Looks like mounts already does this with the mounts ns, and we don't
need it for uts.  Something to watch in any upcoming network patches
though.

thanks
-serge

> 
> Signed-off-by: Eric W. Biederman <ebiederm at xmission.com>
> ---
>  ipc/util.c |   58 +++++++++++++++++++++++++++++++++++++++++++++-------------
>  1 files changed, 45 insertions(+), 13 deletions(-)
> 
> diff --git a/ipc/util.c b/ipc/util.c
> index a9b7a22..7fd10f1 100644
> --- a/ipc/util.c
> +++ b/ipc/util.c
> @@ -739,14 +739,20 @@ int ipc_parse_version (int *cmd)
>  #endif /* __ARCH_WANT_IPC_PARSE_VERSION */
>  
>  #ifdef CONFIG_PROC_FS
> +struct ipc_proc_iter {
> +	struct ipc_namespace *ns;
> +	struct ipc_proc_iface *iface;
> +};
> +
>  static void *sysvipc_proc_next(struct seq_file *s, void *it, loff_t *pos)
>  {
> -	struct ipc_proc_iface *iface = s->private;
> +	struct ipc_proc_iter *iter = s->private;
> +	struct ipc_proc_iface *iface = iter->iface;
>  	struct kern_ipc_perm *ipc = it;
>  	loff_t p;
>  	struct ipc_ids *ids;
>  
> -	ids = current->nsproxy->ipc_ns->ids[iface->ids];
> +	ids = iter->ns->ids[iface->ids];
>  
>  	/* If we had an ipc id locked before, unlock it */
>  	if (ipc && ipc != SEQ_START_TOKEN)
> @@ -773,12 +779,13 @@ static void *sysvipc_proc_next(struct seq_file *s, void *it, loff_t *pos)
>   */
>  static void *sysvipc_proc_start(struct seq_file *s, loff_t *pos)
>  {
> -	struct ipc_proc_iface *iface = s->private;
> +	struct ipc_proc_iter *iter = s->private;
> +	struct ipc_proc_iface *iface = iter->iface;
>  	struct kern_ipc_perm *ipc;
>  	loff_t p;
>  	struct ipc_ids *ids;
>  
> -	ids = current->nsproxy->ipc_ns->ids[iface->ids];
> +	ids = iter->ns->ids[iface->ids];
>  
>  	/*
>  	 * Take the lock - this will be released by the corresponding
> @@ -807,21 +814,23 @@ static void *sysvipc_proc_start(struct seq_file *s, loff_t *pos)
>  static void sysvipc_proc_stop(struct seq_file *s, void *it)
>  {
>  	struct kern_ipc_perm *ipc = it;
> -	struct ipc_proc_iface *iface = s->private;
> +	struct ipc_proc_iter *iter = s->private;
> +	struct ipc_proc_iface *iface = iter->iface;
>  	struct ipc_ids *ids;
>  
>  	/* If we had a locked segment, release it */
>  	if (ipc && ipc != SEQ_START_TOKEN)
>  		ipc_unlock(ipc);
>  
> -	ids = current->nsproxy->ipc_ns->ids[iface->ids];
> +	ids = iter->ns->ids[iface->ids];
>  	/* Release the lock we took in start() */
>  	mutex_unlock(&ids->mutex);
>  }
>  
>  static int sysvipc_proc_show(struct seq_file *s, void *it)
>  {
> -	struct ipc_proc_iface *iface = s->private;
> +	struct ipc_proc_iter *iter = s->private;
> +	struct ipc_proc_iface *iface = iter->iface;
>  
>  	if (it == SEQ_START_TOKEN)
>  		return seq_puts(s, iface->header);
> @@ -836,22 +845,45 @@ static struct seq_operations sysvipc_proc_seqops = {
>  	.show  = sysvipc_proc_show,
>  };
>  
> -static int sysvipc_proc_open(struct inode *inode, struct file *file) {
> +static int sysvipc_proc_open(struct inode *inode, struct file *file)
> +{
>  	int ret;
>  	struct seq_file *seq;
> +	struct ipc_proc_iter *iter;
> +
> +	ret = -ENOMEM;
> +	iter = kmalloc(sizeof(*iter), GFP_KERNEL);
> +	if (!iter)
> +		goto out;
>  
>  	ret = seq_open(file, &sysvipc_proc_seqops);
> -	if (!ret) {
> -		seq = file->private_data;
> -		seq->private = PDE(inode)->data;
> -	}
> +	if (ret)
> +		goto out_kfree;
> +
> +	seq = file->private_data;
> +	seq->private = iter;
> +
> +	iter->iface = PDE(inode)->data;
> +	iter->ns    = get_ipc_ns(current->nsproxy->ipc_ns);
> +out:
>  	return ret;
> +out_kfree:
> +	kfree(iter);
> +	goto out;
> +}
> +
> +static int sysvipc_proc_release(struct inode *inode, struct file *file)
> +{
> +	struct seq_file *seq = file->private_data;
> +	struct ipc_proc_iter *iter = seq->private;
> +	put_ipc_ns(iter->ns);
> +	return seq_release_private(inode, file);
>  }
>  
>  static struct file_operations sysvipc_proc_fops = {
>  	.open    = sysvipc_proc_open,
>  	.read    = seq_read,
>  	.llseek  = seq_lseek,
> -	.release = seq_release,
> +	.release = sysvipc_proc_release,
>  };
>  #endif /* CONFIG_PROC_FS */
> -- 
> 1.4.4.1.g278f
> 
> -
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