nfsd: add nfsd_file_acquire_local()

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>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Anna Schumaker <anna.schumaker@oracle.com>

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);
 }
 
 /*

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 */

fs/nfsd/nfsfh.c

@@ -392,6 +392,29 @@ __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)
+{
+	return __fh_verify(NULL, net, cred, client, NULL,
+			   fhp, type, access);
+}
+
 /**
  * fh_verify - filehandle lookup and access checking
  * @rqstp: pointer to current rpc request

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 *);