Re: [PATCH 2/2] fix sys_unshare()+SEM_UNDO: perform an implicit CLONE_SYSVSEMin CLONE_NEWIPC

[Manfred Spraul]

Serge E. Hallyn wrote:
> > Thus all apps right now call unshare(CLONE_NEWIPC|&~CLONE_SYSVSEM).
> > This combination doesn't make much sense. Even worse - it easily causes a 
> > kernel oops.
> > Thus my fix is twofold:
> > - add support for unshare(CLONE_SYSVSEM).
> > - implicitely add CLONE_SYSVSEM to all calls that set CLONE_NEWIPC.
> >     
>
> Right but your fix ignores the fact that you can achieve the same
> result as unshare(CLONE_NEWIPC&~CLONE_SYSVSEM) by doing
> clone(CLONE_NEWIPC|CLONE_SYSVSEM).
>   
Duh, I overlooked that part. You are right.
Hmm - what's the best fix? Implicitely add CLONE_SYSVSEM or return 
-EINVAL if CLONE_SYSVSEM is not set?
I don't care.
Could you write a patch? I probably won't have enough time until the 
next weekend.

> > I have decided against that, it breaks the current ABI.
> > And we gain virtually nothing - most if not all unshare users will be 
> > single threaded apps that do not use sysvsem at all, and even most sysvsem 
> > users do not use SEM_UNDO.
> >     
>
> And most importantly sharing your semundo list but not your sems with
> your parent is silly!
It's only 99% silly: a task might want to have not-yet undone changes in its parent's namespace.
As soon as the task exit, they are undone. Probably the most complex way to implement wait4().


--
Manfred
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