Messages in this thread | | | Date | Mon, 27 Jun 2011 19:40:41 +0200 | From | Oleg Nesterov <> | Subject | Re: arch_ptrace_attach() without ptrace_traceme()? |
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On 06/27, Oleg Nesterov wrote: > > On 06/27, penguin-kernel@i-love.sakura.ne.jp wrote: > > > > Regarding commit f1671f6d "ptrace: fix exit_ptrace() vs ptrace_traceme() race", > > is calling arch_ptrace_attach() when ptrace_traceme() returned 0 without doing > > anything (due to PF_EXITING race) expected behavior? > > Hmm. Good point, I thinks this should be fixed.
But it is not clear how we can fix this, perhaps we should ignore this problem...
arch_ptrace_attach() is inherently racy when PTRACE_TRACEME is called. Please note that f1671f6d did not introduce this race, although I have to admit I didn't notice this problem when I did this patch.
The race with PF_EXITING you described doesn't differ from another scenario. PF_EXITING is not set, ptrace_traceme() actually attaches the caller, but its paren exits and untraces it before it does arch_ptrace_attach().
If only I knew what arch_ptrace_attach() can do in general ;) But probably it should be paired with ptrace_disable(), and it is not called when the tracer detaches on exit anyway. So I think we can ignore this race.
Oleg.
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