Messages in this thread Patch in this message | | | Date | Thu, 3 Apr 2008 14:44:18 -0500 | From | "Serge E. Hallyn" <> | Subject | Re: [RFC, PATCH] fix SEM_UNDO with namespaces |
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Quoting Eric W. Biederman (ebiederm@xmission.com): > Pavel Emelyanov <xemul@openvz.org> writes: > >>> I agree, that we should probably destroy this one when the task calls > >>> unshare, but trying to keep this list relevant is useless. > >>> > >> A very tricky question: Let's assume we have a process with two threads. > >> The undo structure is shared, as per opengroup standard. > >> Now one thread calls unshare(CLONE_NEWIPC). What should happen? We > >> cannot destroy the undo structure, the other thread might be still > >> interested in it. > >> If we allow sys_unshare() for multithreaded processes with CLONE_NEWIPC > >> and without CLONE_SYSVSEM, then we must handle this case. > > > > Hm... I'd simply disable creating any new namespaces for threads. > > I think other namespaces developers agree with me. Serge, Suka, Eric > > what do you think? > > I almost agree. sys_unshare() in a multithreaded process breaks > all kinds of user space libs. So you can only reasonably look at > the problem as what we do with linux tasks that share some things > and not others. The posix/opengroup notion of processes and threads > are a distraction. > > In this case requiring it appears that to require unsharing both > CLONE_SYSVSEM and CLONE_NEWIPC at the same time. (i.e. unshare > of CLONE_SYSVSEM should fail if CLONE_NEWIPC is not also specified). > > Then to make it work we make unshare of SYSVSEM succeed when it is > not shared. > > This looks like about a 5 line patch or two. > > The effect is because we don't support unsharing of SYSVSEM currently > we don't support a threaded process unsharing the ipc namespace. > > Eric
Eric, does the following patch correctly interpret your recommendation?
Pavel does it make sense to you?
thanks, -serge
From 9c85fb3cb80cea1d888c3c253a9fb6e9bc173649 Mon Sep 17 00:00:00 2001 From: Serge E. Hallyn <serue@us.ibm.com> Date: Thu, 3 Apr 2008 12:43:23 -0700 Subject: [PATCH 1/1] ipc namespaces: fix svsem unsharing issue
Refuse to unshare an ipcns if the semundo is shared and we are not requesting a new SYSVSEM
Signed-off-by: Serge E. Hallyn <serue@us.ibm.com> --- ipc/namespace.c | 10 ++++++++++ 1 files changed, 10 insertions(+), 0 deletions(-)
diff --git a/ipc/namespace.c b/ipc/namespace.c index 9171d94..9044505 100644 --- a/ipc/namespace.c +++ b/ipc/namespace.c @@ -48,6 +48,16 @@ struct ipc_namespace *copy_ipcs(unsigned long flags, struct ipc_namespace *ns) if (!(flags & CLONE_NEWIPC)) return ns; + if (!(flags & CLONE_SYSVSEM)) { + if (!current->sysvsem.undo_list) + goto ok; + if (atomic_read(¤t->sysvsem.undo_list->refcnt) == 1) + goto ok; + put_ipc_ns(ns); + return ERR_PTR(-EINVAL); + } + +ok: new_ns = clone_ipc_ns(ns); put_ipc_ns(ns); -- 1.5.3.6
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