Messages in this thread | | | Subject | Re: [PATCH] Fix for ptrace breakage | From | OGAWA Hirofumi <> | Date | Tue, 17 Sep 2002 00:57:57 +0900 |
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Daniel Jacobowitz <dan@debian.org> writes:
> > > Some comments. First of all, you said you fixed a race on > > > current->ptrace and some other bugs - would you mind saying where they > > > were? It's definitely cleaner after your patch but I'd like to > > > understand where you found bugs, since I think you're introducing more. > > > > It's the following > > > > task_t *trace_task = p->parent; > > int ptrace_flag = p->ptrace; > > BUG_ON (ptrace_flag == 0); > > > > __ptrace_unlink(p); > > p->ptrace = ptrace_flag; > > __ptrace_link(p, trace_task); > > We have the tasklist lock. How can there be a race here? The parent > can't detach while we're holding the tasklist lock. If there is a race > with PTRACE_SETOPTIONS, then PTRACE_SETOPTIONS should take the lock.
No. If the real parent don't change ->ptrace, it doesn't need lock.
> > > So you reparent children on the ptrace_list right here. But they still > > > need to go through zap_thread! You're right, the do_notify_parent in > > > zap_thread isn't necessary; it'll be taken care of in sys_wait4. The > > > orphaned pgrp check is still relevant though. > > > > ??? You forget tasklist_lock? > > Huh? > > The problem I am describing is when a child - which will become an > orphaned pgrp when ``father'' dies - is being ptraced at the moment of > ``father''s death. With your patch it will be moved to > reaper->ptrace_children (or child_reaper->ptrace_children) but never > orphaned properly. It'll miss a signal. > > > > If you're going to remove the if, you need to maintain its effect! > > > See: > > > > - if (p->parent != father) { > > > > - BUG_ON(p->parent != p->real_parent); > > > > - return; > > > > - } > > > > > > This is the case where we were tracing something. The ptrace_unlink > > > returned it to its original parent. It doesn't need the > > > remove_parent/add_parent (though they are harmless); it does need to > > > avoid the orphaned pgrp check. It may need the do_notify_parent check, > > > which was a bug in the previous code. > > > > What is the basis which you think it is bug? > > The death of a tracing process should not have any effect on the traced > process except to untrace it. It should not go through the orphaning > checks. The orphaning checks assume that the exiting process is the > real parent, and will orphan the pgrp if it is not in the same > session... as its tracer! That's a bug.
Ah, ok. I think, it's longtime (odd) behavior. And you think, it's a bug. Right?
And, both of your and old code has odd behavior. yes? -- OGAWA Hirofumi <hirofumi@mail.parknet.co.jp> - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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