DomainKey-Signature: a=rsa-sha1; c=nofws; d=sourceware.org; h=list-id
	:list-unsubscribe:list-subscribe:list-archive:list-post
	:list-help:sender:from:reply-to:to:subject:date:message-id
	:content-type:content-transfer-encoding:mime-version; q=dns; s=
	default; b=UmlXZx1qLrcgNdZuiGhmJhWbrMiToXjp/4/P8YWoHwrgpmE65f3z3
	Il2G0XNas21IC995iKzC/BhVb4DSlrQi85LYeaL0cvJ36/CuFS5bCdoCShLBNL75
	esiCjlkpyAqF39dnKh6V7TT7SdpnEP9W2bd8yHxWYrWx82g/fkroEo=
Mailing-List: contact cygwin-help@cygwin.com; run by ezmlm
Sender: cygwin-owner@cygwin.com
Mail-Followup-To: cygwin@cygwin.com
IronPort-SDR: BHjT0iPWYNgv4NsUTXTdbUQgAC3yTlStRhS5Ih4Cmr/nmh83L1caXUUsPsOV5K/DxCRAyp8T41 LMJQUU+4ooDQ==
From: "Lavrentiev, Anton (NIH/NLM/NCBI) [C] via cygwin" <cygwin@cygwin.com>
Reply-To: "Lavrentiev, Anton (NIH/NLM/NCBI) [C]" <lavr@ncbi.nlm.nih.gov>
To: "'cygwin@cygwin.com'" <cygwin@cygwin.com>
Subject: Empty file without "x" permission is successfully executable on Cygwin
Date: Mon, 5 Aug 2019 18:18:52 +0000
Message-ID: <BL0PR0901MB43081893EE588BDED05886BFA5DA0@BL0PR0901MB4308.namprd09.prod.outlook.com>
Content-Type: text/plain; charset="us-ascii"
MIME-Version: 1.0
X-MS-Exchange-CrossTenant-userprincipalname: lavr@nih.gov
Content-Transfer-Encoding: 8bit
X-MIME-Autoconverted: from quoted-printable to 8bit by delorie.com id x75IJWvM012597

Hi,

Please consider the following shell session:

$ cat dummy.c
#include <stdio.h>

int main()
{
    return 0;
}
$ gcc -o dummy dummy.c
$ mv dummy.exe dummy
$ ./dummy
$ echo $?
0
$ chmod a-x dummy
$ ./dummy
-bash: ./dummy: Permission denied
$ rm dummy
$ touch dummy
$ ./dummy
$ echo $?
0

So Cygwin lets the shell to execute a zero-sized file regardless of the "x" perm
(non-empty files are not executable if they do not have "x", as shown above).

Is that expected?  On Unix, an empty file can only be executed (exit code 0) if there's the "x" permission granted.

There's more.  If I put some rubbish in a file, Cygwin still tries to execute it even if the "x" is not there:

$ rm dummy
$ echo "1" > dummy
$ ./dummy
./dummy: line 1: 1: command not found

So Cygwin knows about "dummy" being a PE32 executable missing the "x" (top of my session), and properly denies the execution
when there's no "x", but still lets all other file contents execute blindly (regardless of "x").  That's very dangerous!

Thanks,
Anton Lavrentiev


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