[Click] [PATCH] do not access deleted timers

[Eddie Kohler]

Hi Nadi,

Great find, and thanks very much for the fix!  We don't tend to use Click with 
highly dynamic timer sets, so bugs are still around.  Your code looks good, 
but unhappy with the extra char allocations, I tried to fix it in a different 
way.  Please try

http://www.read.cs.ucla.edu/gitweb?p=click;a=commit;h=91470b0740c7a019680b9362f15cdab96f7b08c0

and let me know if you still have problems.  Again, thanks for the debugging 
and patch.

Eddie


Nadi Sarrar wrote:
> Hi,
> 
> a problem with the current timer implementation in Click leads to execution of
> unscheduled timers or access to already deleted timers, which can result in any
> kind of unexpected behavior including segmentation faults at unrelated code
> sections, which made it fun to debug :) Possible patch attached.
> 
> The problem occurs only under certain conditions:
> 
>   1) A lot of timers (more than max_timers = 64) must be used that are
>      scheduled with close expiration times.
>   2) Timer handler functions delete (or unschedule) other timers.
>   3) High load helps to trigger this bug fast.
> 
> The problematic code section is in Master::run_timers(), right after the usual
> handling of scheduled timers. There, all scheduled and expired timers are taken
> out of the heap, stored in a vector and then run sequentially, while missing a
> check whether the current timer is still alive (could be deleted/unscheduled by
> one of the previously run timers).
> 
> Nadi
> 
> 
> 
> ------------------------------------------------------------------------
> 
> _______________________________________________
> click mailing list
> click at amsterdam.lcs.mit.edu
> https://amsterdam.lcs.mit.edu/mailman/listinfo/click