On 06.07.20 14:52, Jann Horn wrote:

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On Mon, Jul 6, 2020 at 2:27 PM Alexander Graf [off-list ref] wrote:

quoted

Unless we create a vsyscall that returns both the PID as well as the
epoch and thus handles fork *and* suspend. I need to think about this a
bit more :).

You can't reliably detect forking by checking the PID if it is
possible for multiple forks to be chained before the reuse check runs:

  - pid 1000 remembers its PID
  - pid 1000 forks, creating child pid 1001
  - pid 1000 exits and is waited on by init
  - the pid allocator wraps around
  - pid 1001 forks, creating child pid 1000
  - child with pid 1000 tries to check for forking, determines that its
PID is 1000, and concludes that it is still the original process

Fair point. However, you could bump an epoch value on fork, no? I don't 
think we map anything in the vdso per-process today though ...


Alex



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