Re: [PATCH 5/5 v4] nfsd: Allows user un-mounting filesystem where nfsd exports base on

["J. Bruce Fields" <bfields@fieldses.org>]

I'm not completely sure I understand, but it looks to me like it still
has the flaw Al described: you're allowing the server to use the mount
(and take further references on it) based only on having a pin.

--b.

On Sat, Jun 06, 2015 at 10:41:57PM +0800, Kinglong Mee wrote:
> If there are some mount points(not exported for nfs) under pseudo root,
> after client's operation of those entry under the root, anyone *can't*
> unmount those mount points until export cache expired.
> 
> /nfs/xfs        *(rw,insecure,no_subtree_check,no_root_squash)
> /nfs/pnfs       *(rw,insecure,no_subtree_check,no_root_squash)
> total 0
> drwxr-xr-x. 3 root root 84 Apr 21 22:27 pnfs
> drwxr-xr-x. 3 root root 84 Apr 21 22:27 test
> drwxr-xr-x. 2 root root  6 Apr 20 22:01 xfs
> Filesystem                      1K-blocks    Used Available Use% Mounted on
> ......
> /dev/sdd                          1038336   32944   1005392   4% /nfs/pnfs
> /dev/sdc                         10475520   32928  10442592   1% /nfs/xfs
> /dev/sde                           999320    1284    929224   1% /nfs/test
> /mnt/pnfs/:
> total 0
> -rw-r--r--. 1 root root 0 Apr 21 22:23 attr
> drwxr-xr-x. 2 root root 6 Apr 21 22:19 tmp
> 
> /mnt/xfs/:
> total 0
> umount: /nfs/test/: target is busy
>         (In some cases useful info about processes that
> 	use the device is found by lsof(8) or fuser(1).)
> 
> It's caused by exports cache of nfsd holds the reference of
> the path (here is /nfs/test/), so, it can't be umounted.
> 
> I don't think that's user expect, they want umount /nfs/test/.
> Bruce think user can also umount /nfs/pnfs/ and /nfs/xfs.
> 
> Also, using kzalloc for all memory allocating without kmalloc.
> Thanks for Al Viro's commets for the logic of fs_pin.
> 
> v3,
> 1. using path_get_pin/path_put_unpin for path pin
> 2. using kzalloc for memory allocating
> 
> v4,
> 1. add a completion for pin_kill waiting the reference is decreased to zero.
> 2. add a work_struct for pin_kill decreases the reference indirectly.
> 3. free svc_export/svc_expkey in pin_kill, not svc_export_put/svc_expkey_put.
> 4. svc_export_put/svc_expkey_put go though pin_kill logic.
> 
> Signed-off-by: Kinglong Mee <kinglongmee@gmail.com>
> ---
>  fs/nfsd/export.c | 96 +++++++++++++++++++++++++++++++++++++++++++++-----------
>  fs/nfsd/export.h | 18 ++++++++++-
>  2 files changed, 95 insertions(+), 19 deletions(-)
> 
> diff --git a/fs/nfsd/export.c b/fs/nfsd/export.c
> index f79521a..d3e59bc 100644
> --- a/fs/nfsd/export.c
> +++ b/fs/nfsd/export.c
> @@ -37,15 +37,23 @@
>  #define	EXPKEY_HASHMAX		(1 << EXPKEY_HASHBITS)
>  #define	EXPKEY_HASHMASK		(EXPKEY_HASHMAX -1)
>  
> +static void expkey_destroy(struct svc_expkey *key)
> +{
> +	auth_domain_put(key->ek_client);
> +	kfree_rcu(key, rcu_head);
> +}
> +
>  static void expkey_put(struct kref *ref)
>  {
>  	struct svc_expkey *key = container_of(ref, struct svc_expkey, h.ref);
>  
>  	if (test_bit(CACHE_VALID, &key->h.flags) &&
> -	    !test_bit(CACHE_NEGATIVE, &key->h.flags))
> -		path_put(&key->ek_path);
> -	auth_domain_put(key->ek_client);
> -	kfree(key);
> +	    !test_bit(CACHE_NEGATIVE, &key->h.flags)) {
> +		rcu_read_lock();
> +		complete(&key->ek_done);
> +		pin_kill(&key->ek_pin);
> +	} else
> +		expkey_destroy(key);
>  }
>  
>  static void expkey_request(struct cache_detail *cd,
> @@ -83,7 +91,7 @@ static int expkey_parse(struct cache_detail *cd, char *mesg, int mlen)
>  		return -EINVAL;
>  	mesg[mlen-1] = 0;
>  
> -	buf = kmalloc(PAGE_SIZE, GFP_KERNEL);
> +	buf = kzalloc(PAGE_SIZE, GFP_KERNEL);
>  	err = -ENOMEM;
>  	if (!buf)
>  		goto out;
> @@ -120,6 +128,7 @@ static int expkey_parse(struct cache_detail *cd, char *mesg, int mlen)
>  		goto out;
>  
>  	key.ek_client = dom;	
> +	key.cd = cd;
>  	key.ek_fsidtype = fsidtype;
>  	memcpy(key.ek_fsid, buf, len);
>  
> @@ -210,6 +219,25 @@ static inline void expkey_init(struct cache_head *cnew,
>  	new->ek_fsidtype = item->ek_fsidtype;
>  
>  	memcpy(new->ek_fsid, item->ek_fsid, sizeof(new->ek_fsid));
> +	new->cd = item->cd;
> +}
> +
> +static void expkey_pin_kill(struct fs_pin *pin)
> +{
> +	struct svc_expkey *key = container_of(pin, struct svc_expkey, ek_pin);
> +
> +	if (!completion_done(&key->ek_done)) {
> +		schedule_work(&key->ek_work);
> +		wait_for_completion(&key->ek_done);
> +	}
> +	path_put_unpin(&key->ek_path, &key->ek_pin);
> +	expkey_destroy(key);
> +}
> +
> +static void expkey_close_work(struct work_struct *work)
> +{
> +	struct svc_expkey *key = container_of(work, struct svc_expkey, ek_work);
> +	cache_force_expire(key->cd, &key->h);
>  }
>  
>  static inline void expkey_update(struct cache_head *cnew,
> @@ -218,16 +246,19 @@ static inline void expkey_update(struct cache_head *cnew,
>  	struct svc_expkey *new = container_of(cnew, struct svc_expkey, h);
>  	struct svc_expkey *item = container_of(citem, struct svc_expkey, h);
>  
> +	init_fs_pin(&new->ek_pin, expkey_pin_kill);
>  	new->ek_path = item->ek_path;
> -	path_get(&item->ek_path);
> +	path_get_pin(&new->ek_path, &new->ek_pin);
>  }
>  
>  static struct cache_head *expkey_alloc(void)
>  {
> -	struct svc_expkey *i = kmalloc(sizeof(*i), GFP_KERNEL);
> -	if (i)
> +	struct svc_expkey *i = kzalloc(sizeof(*i), GFP_KERNEL);
> +	if (i) {
> +		INIT_WORK(&i->ek_work, expkey_close_work);
> +		init_completion(&i->ek_done);
>  		return &i->h;
> -	else
> +	} else
>  		return NULL;
>  }
>  
> @@ -306,14 +337,21 @@ static void nfsd4_fslocs_free(struct nfsd4_fs_locations *fsloc)
>  	fsloc->locations = NULL;
>  }
>  
> -static void svc_export_put(struct kref *ref)
> +static void svc_export_destroy(struct svc_export *exp)
>  {
> -	struct svc_export *exp = container_of(ref, struct svc_export, h.ref);
> -	path_put(&exp->ex_path);
>  	auth_domain_put(exp->ex_client);
>  	nfsd4_fslocs_free(&exp->ex_fslocs);
>  	kfree(exp->ex_uuid);
> -	kfree(exp);
> +	kfree_rcu(exp, rcu_head);
> +}
> +
> +static void svc_export_put(struct kref *ref)
> +{
> +	struct svc_export *exp = container_of(ref, struct svc_export, h.ref);
> +
> +	rcu_read_lock();
> +	complete(&exp->ex_done);
> +	pin_kill(&exp->ex_pin);
>  }
>  
>  static void svc_export_request(struct cache_detail *cd,
> @@ -520,7 +558,7 @@ static int svc_export_parse(struct cache_detail *cd, char *mesg, int mlen)
>  		return -EINVAL;
>  	mesg[mlen-1] = 0;
>  
> -	buf = kmalloc(PAGE_SIZE, GFP_KERNEL);
> +	buf = kzalloc(PAGE_SIZE, GFP_KERNEL);
>  	if (!buf)
>  		return -ENOMEM;
>  
> @@ -694,15 +732,34 @@ static int svc_export_match(struct cache_head *a, struct cache_head *b)
>  		path_equal(&orig->ex_path, &new->ex_path);
>  }
>  
> +static void export_pin_kill(struct fs_pin *pin)
> +{
> +	struct svc_export *exp = container_of(pin, struct svc_export, ex_pin);
> +
> +	if (!completion_done(&exp->ex_done)) {
> +		schedule_work(&exp->ex_work);
> +		wait_for_completion(&exp->ex_done);
> +	}
> +	path_put_unpin(&exp->ex_path, &exp->ex_pin);
> +	svc_export_destroy(exp);
> +}
> +
> +static void export_close_work(struct work_struct *work)
> +{
> +	struct svc_export *exp = container_of(work, struct svc_export, ex_work);
> +	cache_force_expire(exp->cd, &exp->h);
> +}
> +
>  static void svc_export_init(struct cache_head *cnew, struct cache_head *citem)
>  {
>  	struct svc_export *new = container_of(cnew, struct svc_export, h);
>  	struct svc_export *item = container_of(citem, struct svc_export, h);
>  
> +	init_fs_pin(&new->ex_pin, export_pin_kill);
>  	kref_get(&item->ex_client->ref);
>  	new->ex_client = item->ex_client;
>  	new->ex_path = item->ex_path;
> -	path_get(&item->ex_path);
> +	path_get_pin(&new->ex_path, &new->ex_pin);
>  	new->ex_fslocs.locations = NULL;
>  	new->ex_fslocs.locations_count = 0;
>  	new->ex_fslocs.migrated = 0;
> @@ -740,10 +797,12 @@ static void export_update(struct cache_head *cnew, struct cache_head *citem)
>  
>  static struct cache_head *svc_export_alloc(void)
>  {
> -	struct svc_export *i = kmalloc(sizeof(*i), GFP_KERNEL);
> -	if (i)
> +	struct svc_export *i = kzalloc(sizeof(*i), GFP_KERNEL);
> +	if (i) {
> +		INIT_WORK(&i->ex_work, export_close_work);
> +		init_completion(&i->ex_done);
>  		return &i->h;
> -	else
> +	} else
>  		return NULL;
>  }
>  
> @@ -811,6 +870,7 @@ exp_find_key(struct cache_detail *cd, struct auth_domain *clp, int fsid_type,
>  
>  	key.ek_client = clp;
>  	key.ek_fsidtype = fsid_type;
> +	key.cd = cd;
>  	memcpy(key.ek_fsid, fsidv, key_len(fsid_type));
>  
>  	ek = svc_expkey_lookup(cd, &key);
> diff --git a/fs/nfsd/export.h b/fs/nfsd/export.h
> index 1f52bfc..ff8905d 100644
> --- a/fs/nfsd/export.h
> +++ b/fs/nfsd/export.h
> @@ -4,6 +4,7 @@
>  #ifndef NFSD_EXPORT_H
>  #define NFSD_EXPORT_H
>  
> +#include <linux/fs_pin.h>
>  #include <linux/sunrpc/cache.h>
>  #include <uapi/linux/nfsd/export.h>
>  
> @@ -46,6 +47,8 @@ struct exp_flavor_info {
>  
>  struct svc_export {
>  	struct cache_head	h;
> +	struct cache_detail	*cd;
> +
>  	struct auth_domain *	ex_client;
>  	int			ex_flags;
>  	struct path		ex_path;
> @@ -58,7 +61,13 @@ struct svc_export {
>  	struct exp_flavor_info	ex_flavors[MAX_SECINFO_LIST];
>  	enum pnfs_layouttype	ex_layout_type;
>  	struct nfsd4_deviceid_map *ex_devid_map;
> -	struct cache_detail	*cd;
> +
> +	struct fs_pin		ex_pin;
> +	struct rcu_head		rcu_head;
> +
> +	/* For cache_put and fs umounting window */
> +	struct completion	ex_done;
> +	struct work_struct	ex_work;
>  };
>  
>  /* an "export key" (expkey) maps a filehandlefragement to an
> @@ -67,12 +76,19 @@ struct svc_export {
>   */
>  struct svc_expkey {
>  	struct cache_head	h;
> +	struct cache_detail	*cd;
>  
>  	struct auth_domain *	ek_client;
>  	int			ek_fsidtype;
>  	u32			ek_fsid[6];
>  
>  	struct path		ek_path;
> +	struct fs_pin		ek_pin;
> +	struct rcu_head		rcu_head;
> +
> +	/* For cache_put and fs umounting window */
> +	struct completion	ek_done;
> +	struct work_struct	ek_work;
>  };
>  
>  #define EX_ISSYNC(exp)		(!((exp)->ex_flags & NFSEXP_ASYNC))
> -- 
> 2.4.2