Re: [PATCH v14 09/25] nfsd: add nfsd_file_acquire_local()

[Mike Snitzer <snitzer@kernel.org>]

On Thu, Aug 29, 2024 at 11:47:22AM -0400, Chuck Lever wrote:
> On Wed, Aug 28, 2024 at 09:04:04PM -0400, Mike Snitzer wrote:
> > From: NeilBrown <neilb@suse.de>
> > 
> > nfsd_file_acquire_local() can be used to look up a file by filehandle
> > without having a struct svc_rqst.  This can be used by NFS LOCALIO to
> > allow the NFS client to bypass the NFS protocol to directly access a
> > file provided by the NFS server which is running in the same kernel.
> > 
> > In nfsd_file_do_acquire() care is taken to always use fh_verify() if
> > rqstp is not NULL (as is the case for non-LOCALIO callers).  Otherwise
> > the non-LOCALIO callers will not supply the correct and required
> > arguments to __fh_verify (e.g. gssclient isn't passed).
> > 
> > Introduce fh_verify_local() wrapper around __fh_verify to make it
> > clear that LOCALIO is intended caller.
> > 
> > Also, use GC for nfsd_file returned by nfsd_file_acquire_local.  GC
> > offers performance improvements if/when a file is reopened before
> > launderette cleans it from the filecache's LRU.
> > 
> > Suggested-by: Jeff Layton <jlayton@kernel.org> # use filecache's GC
> > Signed-off-by: NeilBrown <neilb@suse.de>
> > Co-developed-by: Mike Snitzer <snitzer@kernel.org>
> > Signed-off-by: Mike Snitzer <snitzer@kernel.org>
> > Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
> > ---
> >  fs/nfsd/filecache.c | 71 ++++++++++++++++++++++++++++++++++++++++-----
> >  fs/nfsd/filecache.h |  3 ++
> >  fs/nfsd/nfsfh.c     | 39 +++++++++++++++++++++++++
> >  fs/nfsd/nfsfh.h     |  2 ++
> >  4 files changed, 108 insertions(+), 7 deletions(-)
> > 
> > diff --git a/fs/nfsd/filecache.c b/fs/nfsd/filecache.c
> > index 9e9d246f993c..2dc72de31f61 100644
> > --- a/fs/nfsd/filecache.c
> > +++ b/fs/nfsd/filecache.c
> > @@ -982,12 +982,14 @@ nfsd_file_is_cached(struct inode *inode)
> >  }
> >  
> >  static __be32
> > -nfsd_file_do_acquire(struct svc_rqst *rqstp, struct svc_fh *fhp,
> > +nfsd_file_do_acquire(struct svc_rqst *rqstp, struct net *net,
> > +		     struct svc_cred *cred,
> > +		     struct auth_domain *client,
> > +		     struct svc_fh *fhp,
> >  		     unsigned int may_flags, struct file *file,
> >  		     struct nfsd_file **pnf, bool want_gc)
> >  {
> >  	unsigned char need = may_flags & NFSD_FILE_MAY_MASK;
> > -	struct net *net = SVC_NET(rqstp);
> >  	struct nfsd_file *new, *nf;
> >  	bool stale_retry = true;
> >  	bool open_retry = true;
> > @@ -996,8 +998,13 @@ nfsd_file_do_acquire(struct svc_rqst *rqstp, struct svc_fh *fhp,
> >  	int ret;
> >  
> >  retry:
> > -	status = fh_verify(rqstp, fhp, S_IFREG,
> > -				may_flags|NFSD_MAY_OWNER_OVERRIDE);
> > +	if (rqstp) {
> > +		status = fh_verify(rqstp, fhp, S_IFREG,
> > +				   may_flags|NFSD_MAY_OWNER_OVERRIDE);
> > +	} else {
> > +		status = fh_verify_local(net, cred, client, fhp, S_IFREG,
> > +					 may_flags|NFSD_MAY_OWNER_OVERRIDE);
> > +	}
> >  	if (status != nfs_ok)
> >  		return status;
> >  	inode = d_inode(fhp->fh_dentry);
> > @@ -1143,7 +1150,8 @@ __be32
> >  nfsd_file_acquire_gc(struct svc_rqst *rqstp, struct svc_fh *fhp,
> >  		     unsigned int may_flags, struct nfsd_file **pnf)
> >  {
> > -	return nfsd_file_do_acquire(rqstp, fhp, may_flags, NULL, pnf, true);
> > +	return nfsd_file_do_acquire(rqstp, SVC_NET(rqstp), NULL, NULL,
> > +				    fhp, may_flags, NULL, pnf, true);
> >  }
> >  
> >  /**
> > @@ -1167,7 +1175,55 @@ __be32
> >  nfsd_file_acquire(struct svc_rqst *rqstp, struct svc_fh *fhp,
> >  		  unsigned int may_flags, struct nfsd_file **pnf)
> >  {
> > -	return nfsd_file_do_acquire(rqstp, fhp, may_flags, NULL, pnf, false);
> > +	return nfsd_file_do_acquire(rqstp, SVC_NET(rqstp), NULL, NULL,
> > +				    fhp, may_flags, NULL, pnf, false);
> > +}
> > +
> > +/**
> > + * nfsd_file_acquire_local - Get a struct nfsd_file with an open file for localio
> > + * @net: The network namespace in which to perform a lookup
> > + * @cred: the user credential with which to validate access
> > + * @client: the auth_domain for LOCALIO lookup
> > + * @fhp: the NFS filehandle of the file to be opened
> > + * @may_flags: NFSD_MAY_ settings for the file
> > + * @pnf: OUT: new or found "struct nfsd_file" object
> > + *
> > + * This file lookup interface provide access to a file given the
> > + * filehandle and credential.  No connection-based authorisation
> > + * is performed and in that way it is quite different to other
> > + * file access mediated by nfsd.  It allows a kernel module such as the NFS
> > + * client to reach across network and filesystem namespaces to access
> > + * a file.  The security implications of this should be carefully
> > + * considered before use.
> > + *
> > + * The nfsd_file object returned by this API is reference-counted
> > + * and garbage-collected. The object is retained for a few
> > + * seconds after the final nfsd_file_put() in case the caller
> > + * wants to re-use it.
> > + *
> > + * Return values:
> > + *   %nfs_ok - @pnf points to an nfsd_file with its reference
> > + *   count boosted.
> > + *
> > + * On error, an nfsstat value in network byte order is returned.
> > + */
> > +__be32
> > +nfsd_file_acquire_local(struct net *net, struct svc_cred *cred,
> > +			struct auth_domain *client, struct svc_fh *fhp,
> > +			unsigned int may_flags, struct nfsd_file **pnf)
> > +{
> > +	/*
> > +	 * Save creds before calling nfsd_file_do_acquire() (which calls
> > +	 * nfsd_setuser). Important because caller (LOCALIO) is from
> > +	 * client context.
> > +	 */
> > +	const struct cred *save_cred = get_current_cred();
> > +	__be32 beres;
> > +
> > +	beres = nfsd_file_do_acquire(NULL, net, cred, client,
> > +				     fhp, may_flags, NULL, pnf, true);
> > +	revert_creds(save_cred);
> > +	return beres;
> >  }
> >  
> >  /**
> > @@ -1193,7 +1249,8 @@ nfsd_file_acquire_opened(struct svc_rqst *rqstp, struct svc_fh *fhp,
> >  			 unsigned int may_flags, struct file *file,
> >  			 struct nfsd_file **pnf)
> >  {
> > -	return nfsd_file_do_acquire(rqstp, fhp, may_flags, file, pnf, false);
> > +	return nfsd_file_do_acquire(rqstp, SVC_NET(rqstp), NULL, NULL,
> > +				    fhp, may_flags, file, pnf, false);
> >  }
> >  
> >  /*
> > diff --git a/fs/nfsd/filecache.h b/fs/nfsd/filecache.h
> > index 3fbec24eea6c..26ada78b8c1e 100644
> > --- a/fs/nfsd/filecache.h
> > +++ b/fs/nfsd/filecache.h
> > @@ -66,5 +66,8 @@ __be32 nfsd_file_acquire(struct svc_rqst *rqstp, struct svc_fh *fhp,
> >  __be32 nfsd_file_acquire_opened(struct svc_rqst *rqstp, struct svc_fh *fhp,
> >  		  unsigned int may_flags, struct file *file,
> >  		  struct nfsd_file **nfp);
> > +__be32 nfsd_file_acquire_local(struct net *net, struct svc_cred *cred,
> > +			       struct auth_domain *client, struct svc_fh *fhp,
> > +			       unsigned int may_flags, struct nfsd_file **pnf);
> >  int nfsd_file_cache_stats_show(struct seq_file *m, void *v);
> >  #endif /* _FS_NFSD_FILECACHE_H */
> > diff --git a/fs/nfsd/nfsfh.c b/fs/nfsd/nfsfh.c
> > index 80c06e170e9a..49468e478d23 100644
> > --- a/fs/nfsd/nfsfh.c
> > +++ b/fs/nfsd/nfsfh.c
> > @@ -301,6 +301,22 @@ static __be32 nfsd_set_fh_dentry(struct svc_rqst *rqstp, struct net *net,
> >  	return error;
> >  }
> >  
> > +/**
> > + * __fh_verify - filehandle lookup and access checking
> > + * @rqstp: RPC transaction context, or NULL
> > + * @net: net namespace in which to perform the export lookup
> > + * @cred: RPC user credential
> > + * @client: RPC auth domain
> > + * @gssclient: RPC GSS auth domain, or NULL
> > + * @fhp: filehandle to be verified
> > + * @type: expected type of object pointed to by filehandle
> > + * @access: type of access needed to object
> > + *
> > + * This internal API can be used by callers who do not have an RPC
> > + * transaction context (ie are not running in an nfsd thread).
> 
> This paragraph is incorrect, since fh_verify(), which has a non-NULL
> @rqstp, also uses this internal API. Another review isn't needed,
> but you should perhaps drop this paragraph before submitting the
> final version.

OK, I reviewed this and thought the "can be" implied optional, so it
still applicable for the localio usecase.  But yeah, I will drop it.

> 
> 
> > + *
> > + * See fh_verify() for further descriptions of @fhp, @type, and @access.
> > + */
> >  static __be32
> >  __fh_verify(struct svc_rqst *rqstp,
> >  	    struct net *net, struct svc_cred *cred,
> > @@ -382,6 +398,29 @@ __fh_verify(struct svc_rqst *rqstp,
> >  	return error;
> >  }
> >  
> > +/**
> > + * fh_verify_local - filehandle lookup and access checking
> > + * @net: net namespace in which to perform the export lookup
> > + * @cred: RPC user credential
> > + * @client: RPC auth domain
> > + * @fhp: filehandle to be verified
> > + * @type: expected type of object pointed to by filehandle
> > + * @access: type of access needed to object
> > + *
> > + * This API can be used by callers who do not have an RPC
> > + * transaction context (ie are not running in an nfsd thread).
> > + *
> > + * See fh_verify() for further descriptions of @fhp, @type, and @access.
> > + */
> > +__be32
> > +fh_verify_local(struct net *net, struct svc_cred *cred,
> > +		struct auth_domain *client, struct svc_fh *fhp,
> > +		umode_t type, int access)
> 
> Yeah: Unneeded @rqstp parameter is gone. Clean.
> 

Yes

> > +{
> > +	return __fh_verify(NULL, net, cred, client, NULL,
> > +			   fhp, type, access);
> > +}
> > +
> >  /**
> >   * fh_verify - filehandle lookup and access checking
> >   * @rqstp: pointer to current rpc request
> > diff --git a/fs/nfsd/nfsfh.h b/fs/nfsd/nfsfh.h
> > index 8d46e203d139..5b7394801dc4 100644
> > --- a/fs/nfsd/nfsfh.h
> > +++ b/fs/nfsd/nfsfh.h
> > @@ -217,6 +217,8 @@ extern char * SVCFH_fmt(struct svc_fh *fhp);
> >   * Function prototypes
> >   */
> >  __be32	fh_verify(struct svc_rqst *, struct svc_fh *, umode_t, int);
> > +__be32	fh_verify_local(struct net *, struct svc_cred *, struct auth_domain *,
> > +			struct svc_fh *, umode_t, int);
> >  __be32	fh_compose(struct svc_fh *, struct svc_export *, struct dentry *, struct svc_fh *);
> >  __be32	fh_update(struct svc_fh *);
> >  void	fh_put(struct svc_fh *);
> > -- 
> > 2.44.0
> > 
> 
> Reviewed-by: Chuck Lever <chuck.lever@oracle.com>
> 
> -- 
> Chuck Lever

Thanks