Avoid object names with '//' to avoid hash inconsistencies (#8946)

This is to fix a situation where an object name incorrectly
is sent with '//' in its path heirarchy, we should reject
such object names because they may be hashed to a set where
the object might not originally belong because, this can
cause situations where once object is uploaded we cannot
delete it anymore.

Fixes #8873

cmd/object-api-input-checks.go

@@ -162,6 +162,7 @@ func checkObjectArgs(ctx context.Context, bucket, object string, obj ObjectLayer
 	if err := checkObjectNameForLengthAndSlash(bucket, object); err != nil {
 		return err
 	}
+
 	// Validates object name validity after bucket exists.
 	if !IsValidObjectName(object) {
 		return ObjectNameInvalid{

cmd/object-api-utils.go

@@ -166,7 +166,10 @@ func IsValidObjectPrefix(object string) bool {
 		return false
 	}
 	// Reject unsupported characters in object name.
-	if strings.ContainsAny(object, "\\") {
+	if strings.ContainsAny(object, `\`) {
+		return false
+	}
+	if strings.Contains(object, `//`) {
 		return false
 	}
 	return true

cmd/object-api-utils_test.go

@@ -122,7 +122,9 @@ func TestIsValidObjectName(t *testing.T) {
 		{" ../etc", false},
 		{"./././", false},
 		{"./etc", false},
-		{"contains-\\-backslash", false},
+		{`contains-\-backslash`, false},
+		{`contains//double/forwardslash`, false},
+		{`//contains/double-forwardslash-prefix`, false},
 		{string([]byte{0xff, 0xfe, 0xfd}), false},
 	}