Potential nil pointer dereference in x/distribution

[gsora]

Summary of Bug

The validateCommunityTax() function implemented here accepts a variable i of type interface{} which is immediately converted to a Dec using a type assertion.

Subsequential call to Dec methods could lead to a nil pointer dereference if i is nil.

Version

Cosmos SDK v0.38

Steps to Reproduce

This Go playground reproduces the issue.

Possible fix

A possible fix could be checking for nil value after the type assertion.

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[alexanderbez]

Indeed true, but when would a Dec or Int parameter ever be nil? We should never allow this. Mainly curious about the code path that allows this.

[gsora]

This behavior has been uncovered while updating our app to Cosmos SDK 0.38, mainly due to bad migrations management: the params struct was full of nil fields because we did not execute the migration procedure correctly.

This seems like a corner case which should never happen (migrations should be executed correctly :) but an error would be better than a raw nil pointer dereference-induced panic().

[alexanderbez]

I see. No harm in being extra safe 👌

[alessio]

@alexanderbez The Dec structure cannot be nil. Though the embedded *big.Int could. Attaching Dec structure declaration for reader's convenience:

type Dec struct {
	i *big.Int
}

[alexanderbez]

I already knew that @alessio ;-)