Move Map hash seed to runtime - #1716
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Map and Set objects can be accessed from a context other than the one that created them. With a per-context hash seed, insertion and lookup may select different buckets. Store the seed on JSRuntime so every context sharing these objects uses the same hash seed. Signed-off-by: Yan-Jie Wang <yanjiewtw@gmail.com>
bnoordhuis
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Sep 13, 2026
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LGTM with comments.
The reason I put the hash seed on JSContext instead of JSRuntime is that the latter is often far longer-lived, making it easier to guess.
I suppose that can be mitigated to some extent by reseeding in JS_FreeContext if the context being freed is the runtime's last context.
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| random_state = js__gettimeofday_us(); | ||
| if (random_state == 0) | ||
| random_state = 1; | ||
| rt->hash_seed = xorshift64star(&random_state); |
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You can simplify this to:
Suggested change
| random_state = js__gettimeofday_us(); | |
| if (random_state == 0) | |
| random_state = 1; | |
| rt->hash_seed = xorshift64star(&random_state); | |
| // TODO(bnoordhuis) use getrandom() etc. | |
| rt->hash_seed = js__gettimeofday_us(); |
Using xorshift doesn't add any additional protection; if an adversary can guess the startup timestamp, he can also apply a xorshift to it.
| { | ||
| JSRuntime *rt; | ||
| JSMallocState ms; | ||
| uint64_t random_state; |
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| uint64_t random_state; |
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Map and Set objects can be accessed from a context other than the one that created them. With a per-context hash seed, insertion and lookup may select different buckets.
Store the seed on JSRuntime so every context sharing these objects uses the same hash seed.