[PATCH 15/18] nfsd: reduce want-write range in nfsd4_create_file(

From: NeilBrown <neil-+NVA1uvv1dVBDLzU/[email protected]>

nfsd4_create_file() needs write access to the mount for two purposes:

1/ to create/open the file.
2/ to set attributes on the newly created file.

Normally a file being created would be open for write, and once we have
an active open we have the write access needed for a setattr.
However if a file were created but opened read-only then the setattr
wouldn't necessarily have write access to the mount.

Currently this is all handled by holding the write access across the
open and the setattr.  A subsequent patch will necessarily change how
write access is gained for the open.  So we reduce the range for the
first want_write, and add another one only if setattr is needed on a
read-only open.

Signed-off-by: NeilBrown <neil-+NVA1uvv1dVBDLzU/[email protected]>
---
 fs/nfsd/nfs4proc.c | 27 +++++++++++++++++++++++----
 1 file changed, 23 insertions(+), 4 deletions(-)

diff --git a/fs/nfsd/nfs4proc.c b/fs/nfsd/nfs4proc.c
index 03eb93f696f9..5bd19e5d9e34 100644
--- a/fs/nfsd/nfs4proc.c
+++ b/fs/nfsd/nfs4proc.c
@@ -310,7 +310,7 @@ nfsd4_create_file(struct svc_rqst *rqstp, struct svc_fh *fhp,
 			       &QSTR_LEN(open->op_fname, open->op_fnamelen));
 	if (IS_ERR(child)) {
 		status = nfserrno(PTR_ERR(child));
-		goto out;
+		goto out_write;
 	}
 	path.dentry = child;
 
@@ -323,12 +323,13 @@ nfsd4_create_file(struct svc_rqst *rqstp, struct svc_fh *fhp,
 			end_creating(child);
 			status = nfserrno(PTR_ERR(open->op_filp));
 			open->op_filp = NULL;
-			goto out;
+			goto out_write;
 		}
 
 		open->op_created = open->op_filp->f_mode & FMODE_CREATED;
 	}
 	end_creating(child);
+	fh_drop_write(fhp);
 
 	status = fh_compose(resfhp, fhp->fh_export, child, fhp);
 	if (status != nfs_ok)
@@ -367,7 +368,22 @@ nfsd4_create_file(struct svc_rqst *rqstp, struct svc_fh *fhp,
 	fh_fill_post_attrs(fhp);
 
 	if (is_create_with_attrs(open)) {
-		status = nfsd_create_setattr(rqstp, fhp, resfhp, &attrs);
+		if (((oflags & O_ACCMODE) == O_RDONLY)) {
+			/* We will need write access to set the attrs,
+			 * but a successful open won't provide that.
+			 */
+			int host_err = fh_want_write(fhp);
+			if (host_err) {
+				status = nfserrno(host_err);
+			} else {
+				status = nfsd_create_setattr(rqstp, fhp,
+							     resfhp, &attrs);
+				fh_drop_write(fhp);
+			}
+		} else {
+			status = nfsd_create_setattr(rqstp, fhp,
+						     resfhp, &attrs);
+		}
 
 		if (attrs.na_labelerr)
 			open->op_bmval[2] &= ~FATTR4_WORD2_SECURITY_LABEL;
@@ -380,8 +396,11 @@ nfsd4_create_file(struct svc_rqst *rqstp, struct svc_fh *fhp,
 	}
 out:
 	nfsd_attrs_free(&attrs);
-	fh_drop_write(fhp);
 	return status;
+
+out_write:
+	fh_drop_write(fhp);
+	goto out;
 }
 
 /**
-- 
2.50.0.107.gf914562f5916.dirty