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Re: [help-gnubatch] gbch-xq

From: John Collins (Xi Software Ltd)
Subject: Re: [help-gnubatch] gbch-xq
Date: Sat, 23 Oct 2010 16:06:22 +0100
User-agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv: Gecko/20101006 Lightning/1.0b2 Thunderbird/3.1.5

On 18/10/10 06:32, Jan Schampera wrote:
Todd Jackson wrote:

> gbch-xq: Warning! /home/tjackson/.gnubatch exists but is not readable!

Is it (for the RUID, you)?

 I'm pretty sure this is because this program is setuid gnubatch, but does anyone know a way to avoid having to do the xhost command (and disabling X security)?

This could be managed by separating the display access to RUID and doing the work using the permissions it gets from the SetUID bit. I don't know if this is that easy to do in the current code. Maybe Mr. Collins knows off from head (i.e. playing *UID switching for API access and user interface).
I've been playing around with this and alas the problem is with the GTK+ library.

The GTK+ library aborts if RUID, EUID and Saved-SetUID are not all the same.

The semantics of setreuid(r, e) are that if r is set (even if the effect would be to leave it unchanged) Saved-SetUID is set to the new value of the RUID. (If you put -1 as the new RUID it leaves that and the Saved_SetUID alone). Once Saved-SetUID has been set you can't change it back.

So we need to do either

setreuid(Realuid, Realuid)


setreuid(Effuid, Effuid)

before GTK will work.

If we do the first, then the message queue can't be accessed.

If we do the second, then you need all this "xhost +" before gbch-xq will work and problems with accessing the files if $HOME is set 700.

I suppose it could be set-user root but I have a paranoia (which I know is widespread) about having things set-user root when they shouldn't be.

I think GTK+ ought not be so fascist myself. People know what they're coding. Set-user to something other than root ought to be encouraged not shrouded in mystery.

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