From 890b493a2e32d7f607e5ee0150a9ce884c3e26ff Mon Sep 17 00:00:00 2001
From: Klaus Post <klauspost@gmail.com>
Date: Fri, 22 Nov 2019 09:50:17 -0800
Subject: [PATCH] Use random file name for write check (#8563)

Since there may be multiple writes going on concurrently
Use a random file name for the write check to avoid collisions.
---
 cmd/posix.go | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/cmd/posix.go b/cmd/posix.go
index d19d07dd2..bafebde07 100644
--- a/cmd/posix.go
+++ b/cmd/posix.go
@@ -19,6 +19,8 @@ package cmd
 import (
 	"bufio"
 	"context"
+	"crypto/rand"
+	"encoding/hex"
 	"errors"
 	"io"
 	"io/ioutil"
@@ -154,12 +156,15 @@ func getValidPath(path string) (string, error) {
 	}
 
 	// check if backend is writable.
-	file, err := os.Create(pathJoin(path, ".writable-check.tmp"))
+	var rnd [8]byte
+	_, _ = rand.Read(rnd[:])
+	fn := pathJoin(path, ".writable-check-"+hex.EncodeToString(rnd[:])+".tmp")
+	file, err := os.Create(fn)
 	if err != nil {
 		return path, err
 	}
-	defer os.Remove(pathJoin(path, ".writable-check.tmp"))
 	file.Close()
+	os.Remove(fn)
 
 	return path, nil
 }