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From: "Lavrentiev, Anton (NIH/NLM/NCBI) [C] via cygwin" <cygwin AT cygwin DOT com>
Reply-To: "Lavrentiev, Anton (NIH/NLM/NCBI) [C]" <lavr AT ncbi DOT nlm DOT nih DOT gov>
To: "'cygwin AT cygwin DOT com'" <cygwin AT cygwin DOT com>
Subject: Empty file without "x" permission is successfully executable on Cygwin
Date: Mon, 5 Aug 2019 18:18:52 +0000
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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


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