DKIM-Filter:	OpenDKIM Filter v2.11.0 delorie.com 48OAGlBU2559280
Authentication-Results:	delorie.com;
	dkim=pass (1024-bit key, unprotected) header.d=cygwin.com header.i=@cygwin.com header.a=rsa-sha256 header.s=default header.b=Ijima15P
X-Recipient:	archive-cygwin AT delorie DOT com
DKIM-Filter:	OpenDKIM Filter v2.11.0 sourceware.org 846CE385DDDF
DKIM-Signature:	v=1; a=rsa-sha256; c=relaxed/relaxed; d=cygwin.com;
	s=default; t=1727173005;
	bh=HHgMCp0nX5c1adaADOjRSYy1ahtFkrL2GsOkEtUj6k8=;
	h=Subject:To:References:Date:In-Reply-To:List-Id:List-Unsubscribe:
	List-Archive:List-Post:List-Help:List-Subscribe:From:Reply-To:Cc:
	From;
	b=Ijima15PrxJYVjuOf54X2SBzLl6VooqzmoZdNM7m6hQzn8BU70Z+GxeOtKLjDUDep
	RNkxw6iM24/kicTlz803ZLO3j98Vco0BUiICwuVBG9l7lFtis45YMGpObYvMshHVAK
	jwh7HpCuzeNnILa4F9URvsZO2rTcZ3eOFzA76n0o=
X-Original-To:	cygwin AT cygwin DOT com
Delivered-To:	cygwin AT cygwin DOT com
DMARC-Filter:	OpenDMARC Filter v1.4.2 sourceware.org B34F33858424
ARC-Filter:	OpenARC Filter v1.0.0 sourceware.org B34F33858424
ARC-Seal:	i=1; a=rsa-sha256; d=sourceware.org; s=key; t=1727172946; cv=none;
	b=eLcTr2OYdxfHNGq6njML/OG7fRG4TxCtku5U1nKTZkVk4Oq7pkGaSi6dUh8+CKMQTiscFkSpNvF3W2RIjt9ucoLjWrKmGn/RwKKYXWzDMDJWSSEAGoU5SoqHaMPtOkk9ktF+0WGkNl4/WK7Fg7beiIvsIXCmrNcpu6HOfVaBM5k=
ARC-Message-Signature:	i=1; a=rsa-sha256; d=sourceware.org; s=key;
	t=1727172946; c=relaxed/simple;
	bh=hZFxgy2PrU+VrwDDy4hd55ud5mU77riIqkDTh8C/64A=;
	h=Subject:To:From:Message-ID:Date:MIME-Version;
	b=g+hGV36A0j8LTBZ77/UYfi6iYGMnFeKTKSV+Y9JjnBdG5wMY7ZjVpFQsNJW3v8ppiodmPpuvL5wzdCUwbPoLCLsy3XPUYplykaBi8Th1kmHZ+fSvu28JkOlCTQHsdw/oOv+0EIbJfuXM8POXLm6G5bBqoIMDLHQDKzTwWn0FeDY=
ARC-Authentication-Results:	i=1; server2.sourceware.org
Subject:	Re: pread()/pwrite() fail with EBADF in child process if already used
	before fork()
To:	cygwin AT cygwin DOT com
References:	<13e3c5b1-3c7b-acc4-469e-0542d50cb6f6 AT t-online DOT de>
	<c9dffef7-868e-d10a-520e-e00aa09839a6 AT t-online DOT de>
Message-ID:	<c30667f1-6640-9bca-be72-6f2890ca3191@t-online.de>
Date:	Tue, 24 Sep 2024 12:15:37 +0200
User-Agent:	Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:91.0) Gecko/20100101
	SeaMonkey/2.53.18.2
MIME-Version:	1.0
In-Reply-To:	<c9dffef7-868e-d10a-520e-e00aa09839a6@t-online.de>
X-TOI-EXPURGATEID:	150726::1727172937-F3FFD5D9-D6AA5312/0/0 CLEAN NORMAL
X-TOI-MSGID:	c59fdea9-10d9-4893-a18e-ab5984e985c6
X-Spam-Status:	No, score=-3.5 required=5.0 tests=BAYES_00, BODY_8BITS,
	FREEMAIL_FROM, KAM_DMARC_STATUS, NICE_REPLY_A, RCVD_IN_DNSWL_NONE,
	RCVD_IN_MSPIKE_H3, RCVD_IN_MSPIKE_WL, SPF_HELO_NONE, SPF_PASS,
	TXREP autolearn=ham autolearn_force=no version=3.4.6
X-Spam-Checker-Version:	SpamAssassin 3.4.6 (2021-04-09) on
	server2.sourceware.org
X-BeenThere:	cygwin AT cygwin DOT com
X-Mailman-Version:	2.1.30
List-Id:	General Cygwin discussions and problem reports <cygwin.cygwin.com>
List-Unsubscribe:	<https://cygwin.com/mailman/options/cygwin>,
	<mailto:cygwin-request AT cygwin DOT com?subject=unsubscribe>
List-Archive:	<https://cygwin.com/pipermail/cygwin/>
List-Post:	<mailto:cygwin AT cygwin DOT com>
List-Help:	<mailto:cygwin-request AT cygwin DOT com?subject=help>
List-Subscribe:	<https://cygwin.com/mailman/listinfo/cygwin>,
	<mailto:cygwin-request AT cygwin DOT com?subject=subscribe>
From:	Christian Franke via Cygwin <cygwin AT cygwin DOT com>
Reply-To:	cygwin AT cygwin DOT com
Cc:	Christian Franke <Christian DOT Franke AT t-online DOT de>
Errors-To:	cygwin-bounces~archive-cygwin=delorie DOT com AT cygwin DOT com
Sender:	"Cygwin" <cygwin-bounces~archive-cygwin=delorie DOT com AT cygwin DOT com>
X-MIME-Autoconverted:	from base64 to 8bit by delorie.com id 48OAGlBU2559280

Christian Franke via Cygwin wrote:
> Christian Franke via Cygwin wrote:
>> Found during test of 'stress-ng --pseek ...' from current upstream 
>> stress-ng git HEAD:
>>
>> Testcase:
>>
>> $ uname -r
>> 3.5.4-1.x86_64
>>
>> $ cat pfail.c
>> #include <fcntl.h>
>> #include <stdio.h>
>> #include <unistd.h>
>> #include <sys/wait.h>
>>
>> int main()
>> {
>>   int fd = open("pwrite.tmp", O_RDWR|O_CREAT|O_BINARY, 0666);
>>   if (fd < 0) {
>>     perror("open"); return 1;
>>   }
>>
>>   char c = 42;
>>   if (pwrite(fd, &c, 1, 0) < 0)
>>     perror("pwrite");
>>
>>   if (fork() == 0) {
>>     if (pread(fd, &c, 1, 0) < 0)
>>       perror("pread");
>>     _exit(0);
>>   }
>>
>>   int status;
>>   wait(&status);
>>   return 0;
>> }
>>
>> $ make pfail
>> cc     pfail.c   -o pfail
>>
>> $ ./pfail
>> pread: Bad file descriptor
>>
>> $ strace ./pfail
>> ...
>>   617   75356 [main] pfail 10826 dofork: 10827 = fork()
>>    82   11289 [main] pfail 10827 seterrno_from_nt_status: 
>> /usr/src/debug/cygwin-3.5.4-1/winsup/cygwin/fhandler/disk_file.cc:1883 
>> status 0xC0000008 -> windows error 6
>>    80   75436 [main] pfail 10826 wait4: calling proc_subproc, pid -1, 
>> options 0
>>    76   11365 [main] pfail 10827 geterrno_from_win_error: windows 
>> error 6 == errno 9
>>    78   75514 [main] pfail 10826 proc_subproc: args: 5, -7728
>>    64   11429 [main] pfail 10827 pread: -1 = pread(3, 0x7FFFFCC0B, 1, 
>> 0), errno 9
>> ...
>>
>>
>> The problem does not occur if there is no pread()/pwrite() before the 
>> fork(). This suggests that the child process inherits the extra 
>> handle value used to keep the original seek position, but not the 
>> actual handle.
>>
>
>
> The mentioned extra handle 'prw_handle' is set to null after fork here:
> https://cygwin.com/git/?p=newlib-cygwin.git;a=blob;f=winsup/cygwin/fhandler/disk_file.cc;h=f4c21d3#l1698 
>
>
> But a test suggests that fhandler_disk_file::fixup_after_fork() is 
> never called or debug_printf() does not work if called in this function.

Possible fix: 
https://sourceware.org/pipermail/cygwin-patches/2024q3/012793.html

-- 
Regards,
Christian


-- 
Problem reports:      https://cygwin.com/problems.html
FAQ:                  https://cygwin.com/faq/
Documentation:        https://cygwin.com/docs.html
Unsubscribe info:     https://cygwin.com/ml/#unsubscribe-simple

- Raw text -