This is the mail archive of the cygwin-developers mailing list for the Cygwin project.

Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]
Other format: [Raw text]

Re: Request for help debugging screen problem


On 8/02/2010 11:52 AM, Corinna Vinschen wrote:
On Feb 8 10:53, Shaddy Baddah wrote:
On 8/02/2010 9:51 AM, Corinna Vinschen wrote:
It's the same OpenProcess problem in just another shape.

Just to clarify. If you mean the same problem as reattaching to screen, I think the new developments reveal that I have no data at all on that. It could well be OpenProcess) as well, but I can't determine because screen -r isn't even being run by strace. strace is failing before it executes the process (evidenced by no ls output when I do a strace ls).


With regards to the calling OpenProcess() on the master, I'd like to
outline a disparity here. In my cygwin scenario, the session sshd
process is not owned by the user, but by the same as its parent,

In linux, the session ssh is setuid'ed to the authenticated user.
I'm wondering why this is not the case with cygwin.

It's the fact that a full privilege separation implementation in sshd requires the implementation of descriptor passing via UNIX sockets in Cygwin. That's just not available so far. If you change your sshd_config file on Linux to specify

UsePrivilegeSeparation no

and restart sshd, you will notice that the process

sshd: username [priv]

owned by root is not in the process list anymore and the process

sshd: username@pts/X

process is now owned by root.  That's identical to what happens in
Cygwin all the time.

Thanks for that. I'll give it a try, but I'm sure I'll see the behaviour you described.

My next step is to build screen and try to debug it to a point where
I can find where in the cygwin dll (if in fact it is the cygwin at
fault) that there is an issue. Beyond that, without strace at my
disposal, I'm a bit stuck on how I'm going to debug cygwin. Help
would be appreciated.

Did you notice the how-to-debug-cygwin.txt file in the winsup/cygwin dir? You should build Cygwin with the -DDEBUGGING flag and then you have a couple of options using GDB rather than strace.

No, I didn't notice. I can get a little to eager at times, and miss important steps. Plus I can only devote sporadic time to the issues. I'll read through it and give it a try.


Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]