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From: Orgad Shaneh <orgads@gmail.com>
Date: Wed, 7 Apr 2021 23:47:48 +0300
Message-ID: <CAGHpTBLp33PD_Pa5nGaH-cyfr+0d+Tk=ffqFtBCWP+Jq9VbuPg@mail.gmail.com>
Subject: A problem with noacl+umask+chmod result
To: cygwin@cygwin.com
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X-List-Received-Date: Wed, 07 Apr 2021 20:48:03 -0000

Hi,

If a filesystem is mounted with noacl, calling chmod to add write
permissions after umasking this permission doesn't work. Demonstrated
with command-line and C++.

Did I miss something or is this a real bug? According to umask man, it
should only affect newly created files and directories, but I didn't
find anything that relates to chmod.

Command-line:
touch foo
ls -l foo
# -rw-r--r-- ... foo
umask 200
chmod 0 foo
ls -l foo
# -r--r--r-- ... foo
chmod 200 foo
ls -l foo
# -r--r--r-- ... foo
# Expected to have rw

C++:
#include <unistd.h>
#include <sys/stat.h>
#include <stdlib.h>
#include <fcntl.h>
#include <iostream>

const char fileName[] = "foo";
const int mask = S_IWRITE;

void get()
{
  struct stat st;
  stat(fileName, &st);
  std::cout << (st.st_mode) << std::endl;
}

void set(int mode) {
  chmod(fileName, mode);
}

int main() {
  std::cout << std::oct;
  std::cout << "mask: " << mask << std::endl;
  close(open(fileName, O_WRONLY | O_CREAT));
  get();
  umask(mask);
  set(0);
  get();
  set(mask);
  get();
}

Output without noacl:
mask: 200
100644
100444
100644

Output with noacl:
mask: 200
100644
100444
100444

Thanks,
- Orgad