NFS: alloc_nfs_open_context() must use the file cred when available

If we're creating a nfs_open_context() for a specific file pointer,
we must use the cred assigned to that file.

Fixes: a52458b4 ("NFS/NFSD/SUNRPC: replace generic creds with 'struct cred'.")
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>

fs/nfs/inode.c

@@ -959,16 +959,16 @@ struct nfs_open_context *alloc_nfs_open_context(struct dentry *dentry,
 						struct file *filp)
 {
 	struct nfs_open_context *ctx;
-	const struct cred *cred = get_current_cred();
 
 	ctx = kmalloc(sizeof(*ctx), GFP_KERNEL);
-	if (!ctx) {
-		put_cred(cred);
+	if (!ctx)
 		return ERR_PTR(-ENOMEM);
-	}
 	nfs_sb_active(dentry->d_sb);
 	ctx->dentry = dget(dentry);
-	ctx->cred = cred;
+	if (filp)
+		ctx->cred = get_cred(filp->f_cred);
+	else
+		ctx->cred = get_current_cred();
 	ctx->ll_cred = NULL;
 	ctx->state = NULL;
 	ctx->mode = f_mode;