linux-kernel - Re: [PATCH] nfsd: enable UMH client tracker in container

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Date:	Thu, 25 Apr 2013 11:17:48 +0400
From:	Stanislav Kinsbursky <skinsbursky@...allels.com>
To:	"J. Bruce Fields" <bfields@...ldses.org>
CC:	Jeff Layton <jlayton@...hat.com>, <linux-nfs@...r.kernel.org>,
	<devel@...nvz.org>, <Trond.Myklebust@...app.com>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] nfsd: enable UMH client tracker in container

24.04.2013 00:00, J. Bruce Fields пишет:
> On Fri, Apr 19, 2013 at 07:01:50AM -0700, Jeff Layton wrote:
>> On Tue, 16 Apr 2013 15:17:44 +0400
>> Stanislav Kinsbursky <skinsbursky@...allels.com> wrote:
>>
>>> This patch adds support for UserModeHelper tracker in a container.
>>> The reason for this is that the only containerised tracker ("nfsdcld") is
>>> going to be removed in 3.10 kernel, thus at least one more tracker have to be
>>> containerised to replace the deprecated one.
>>> UMH tracker looks more preferable comparing to legacy since it's the latest
>>> one.
>>> To make UMH tracker work in a container, we have to make sure, that it
>>> executes right binary (i.e., this binary have to be taken from the container
>>> environment).
>>> But, UMH is a kernel thread, which works in global root environment by design
>>> (kernel thread's root is inherited from kthreadd, which in turn inherited it's
>>> root from global init). So, the root have to be swapped to the container's
>>> one before binary execution.
>>>
>>> This patch passes "init" callback and private "data" to UMH interface, which
>>> are used to swap root for spawned kernel thread.
>>>
>>> Note: container's root can be stored on stack, because UMH calls are
>>> synchronous.
>>>
>>> Signed-off-by: Stanislav Kinsbursky <skinsbursky@...allels.com>
>>> ---
>>>   fs/nfsd/nfs4recover.c |   29 ++++++++++++++++++++++-------
>>>   1 files changed, 22 insertions(+), 7 deletions(-)
>>>
>>> diff --git a/fs/nfsd/nfs4recover.c b/fs/nfsd/nfs4recover.c
>>> index 899ca26..15f8de6 100644
>>> --- a/fs/nfsd/nfs4recover.c
>>> +++ b/fs/nfsd/nfs4recover.c
>>> @@ -38,6 +38,7 @@
>>>   #include <linux/crypto.h>
>>>   #include <linux/sched.h>
>>>   #include <linux/fs.h>
>>> +#include <linux/fs_struct.h>
>>>   #include <linux/module.h>
>>>   #include <net/net_namespace.h>
>>>   #include <linux/sunrpc/rpc_pipe_fs.h>
>>> @@ -1122,12 +1123,28 @@ nfsd4_cltrack_legacy_recdir(const struct xdr_netobj *name)
>>>   	return result;
>>>   }
>>>
>>> +static int nfsd_swap_root(struct subprocess_info *info, struct cred *new)
>>> +{
>>> +	struct path *root = info->data;
>>> +	struct fs_struct *fs = current->fs;
>>> +	struct path current_root;
>>> +
>>> +	spin_lock(&fs->lock);
>>> +	current_root = fs->root;
>>> +	fs->root = *root;
>>> +	spin_unlock(&fs->lock);
>>> +	if (current_root.dentry)
>>> +		path_put(&current_root);
>>> +	return 0;
>>> +}
>>> +
>>>   static int
>>>   nfsd4_umh_cltrack_upcall(char *cmd, char *arg, char *legacy)
>>>   {
>>>   	char *envp[2];
>>>   	char *argv[4];
>>>   	int ret;
>>> +	struct path root;
>>>
>>>   	if (unlikely(!cltrack_prog[0])) {
>>>   		dprintk("%s: cltrack_prog is disabled\n", __func__);
>>> @@ -1146,7 +1163,11 @@ nfsd4_umh_cltrack_upcall(char *cmd, char *arg, char *legacy)
>>>   	argv[2] = arg;
>>>   	argv[3] = NULL;
>>>
>>> -	ret = call_usermodehelper(argv[0], argv, envp, UMH_WAIT_PROC);
>>> +	get_fs_root(current->fs, &root);
>>> +
>>> +	ret = call_usermodehelper_fns(argv[0], argv, envp, UMH_WAIT_PROC,
>>> +				       nfsd_swap_root, NULL, &root);
>>> +
>>>   	/*
>>>   	 * Disable the upcall mechanism if we're getting an ENOENT or EACCES
>>>   	 * error. The admin can re-enable it on the fly by using sysfs
>>> @@ -1185,12 +1206,6 @@ bin_to_hex_dup(const unsigned char *src, int srclen)
>>>   static int
>>>   nfsd4_umh_cltrack_init(struct net __attribute__((unused)) *net)
>>>   {
>>> -	/* XXX: The usermode helper s not working in container yet. */
>>> -	if (net != &init_net) {
>>> -		WARN(1, KERN_ERR "NFSD: attempt to initialize umh client "
>>> -			"tracking in a container!\n");
>>> -		return -EINVAL;
>>> -	}
>>>   	return nfsd4_umh_cltrack_upcall("init", NULL, NULL);
>>>   }
>>>
>>>
>>
>> I think this looks correct and like it'll work, but I wonder whether
>> we'd be best served by making this part of the UMH code itself?
>>
>> IOW, add some fields to the struct subprocess_info to hold the new
>> root, and then do what you're doing in nfsd_swap_root before calling
>> the "init" function?
>>
>> I imagine we'll eventually need do something similar for at least some
>> of the callers of call_usermodehelper so it would make sense to me to
>> not replicate copies of nfsd_swap_root all over the place.
>
> Agreed.
>

Hmm. Yes, me too.
Ok, I'll prepare patch for the UMH itself.
And resend.
Thanks, guys.

> --b.
>


-- 
Best regards,
Stanislav Kinsbursky
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