chore: update Timer.md with caveats
#3827
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| to re-establish timers after an upgrade is to walk stable variables | ||
| in the `post_upgrade` hook and distill necessary timer information | ||
| from there. |
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Maybe some will come up with a good example. Maybe we could have made this work using a single well-known update method, but that wasn't in the Rust version either.
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Is this correct?
is to walk stable variables
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Yep, I think it is common usage to walk (i.e. traverse) data structures.
| in the `post_upgrade` hook and distill necessary timer information | ||
| from there. | ||
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| Note: Basing security (e.g. access control) on timers is almost always |
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What's the underlying reason that security controls shouldn't use timers? Or is this based on my comment in slack?
I can't come up with a good scenario in which one would want to. Just wondering if this statements mean that timers are not very reliable or that usually if you need timers in a security control you there is a design issue. The thing we wanted to remark from ProdSec is that IF you use timers for security controls, make sure to reinstate them after an upgrade.
Agreed that access control would likely not need timers.
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It is triggered by your slack comment. There are access control methods that use time, e.g. exponential lockout for mistyped passwords etc. These are problematic here, as there is no protection against reentrancy.
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I have added a blurb. PTAL.
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I missed this comment back then. LGTM if you still want to merge it.
Co-authored-by: Claudio Russo <[email protected]>
Co-authored-by: Claudio Russo <[email protected]>
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Just doing some repo cleanup for better focussing on active work: |
... and suggestions. Touch on security and the default mechanism.
Also linking @dfinity-berestovskyy's timer FAQ, which is https://internetcomputer.org/docs/current/developer-docs/backend/periodic-tasks#timers-library-limitations