share/ipld: newProofCollector should use bits.Len instead of math.Log2 just in case

[odeke-em]

Celestia Node version

d7d2db8

OS

darwin

Install tools

No response

Others

No response

Steps to reproduce it

Read through

celestia-node/share/ipld/proof_collector.go

Line 17 in d7d2db8

height := int(math.Log2(float64(maxShares))) + 1

It isn't a problem nor an attack vector as we deemed offline but if a caller passed in a max shard size of 0, that code could cause a runtime panic because of this result:

log(0) = INFINITY and in Go that's represented by -INF or +INF whichever is implementation defined
which when converted to an integer is the smallest negative value which when passed into make([]T, -value)

Expected result

Zero value allocated for negative values or no crash

Actual result

A runtime panic

Relevant log output

No response

Is the node "stuck"? Has it stopped syncing?

No

Notes

Remedy

We can safely instead use math/bits.Len64 which even if had a negative number would have a maximum of 64 values

and here is a clear exhibit

https://go.dev/play/p/IlSf1wlm3nT

package main

import (
	"math"
	"math/bits"
)

var v = 0

func main() {
	println(math.Log2(float64(v)))
	println(bits.Len64(uint64(v)))
}

which prints out

-Inf
0

and is guaranteed never to panic, because bits.Len64(uint64(positive of negative int)) = [0, 63]
but math.Log2(float64(positive or negative int)) = [-9223372036854775808, 63]

Kindly cc-ing @Wondertan