runtime: opportunistically rotate map key seed

When clearing a map, reinitialize the hash seed with random data. This
makes it more difficult for attackers to trigger pathological
performance via repeated hash collisions.

The extra reinitialization causes no statistically significant slowdown:

name                              old time/op  new time/op  delta
GoMapClear/Reflexive/1-12         18.3ns ± 0%  20.0ns ± 0%   ~             (p=1.000 n=1+1)
GoMapClear/Reflexive/10-12        18.2ns ± 0%  19.8ns ± 0%   ~             (p=1.000 n=1+1)
GoMapClear/Reflexive/100-12       44.6ns ± 0%  46.1ns ± 0%   ~             (p=1.000 n=1+1)
GoMapClear/Reflexive/1000-12       592ns ± 0%   592ns ± 0%   ~     (all samples are equal)
GoMapClear/Reflexive/10000-12     3.88µs ± 0%  3.88µs ± 0%   ~             (p=1.000 n=1+1)
GoMapClear/NonReflexive/1-12      62.7ns ± 0%  63.9ns ± 0%   ~             (p=1.000 n=1+1)
GoMapClear/NonReflexive/10-12     75.0ns ± 0%  76.1ns ± 0%   ~             (p=1.000 n=1+1)
GoMapClear/NonReflexive/100-12     203ns ± 0%   206ns ± 0%   ~             (p=1.000 n=1+1)
GoMapClear/NonReflexive/1000-12   2.33µs ± 0%  2.33µs ± 0%   ~     (all samples are equal)
GoMapClear/NonReflexive/10000-12  18.1µs ± 0%  18.1µs ± 0%   ~             (p=1.000 n=1+1)

Fixes #25237

Change-Id: I629a79dd7c562ba18bd94159673c3b9b653da643
Reviewed-on: https://go-review.googlesource.com/c/go/+/253020
Reviewed-by: Keith Randall <khr@golang.org>
1 file changed
tree: f80cf558128d8b494309675a2107cd72da1c5c06
  1. .gitattributes
  2. .github/
  3. .gitignore
  4. AUTHORS
  5. CONTRIBUTING.md
  6. CONTRIBUTORS
  7. LICENSE
  8. PATENTS
  9. README.md
  10. SECURITY.md
  11. api/
  12. doc/
  13. favicon.ico
  14. lib/
  15. misc/
  16. robots.txt
  17. src/
  18. test/
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