starlark: add maxAlloc guard to list, sorted, enumerate#636
starlark: add maxAlloc guard to list, sorted, enumerate#636YuvalFradkin1 wants to merge 1 commit intogoogle:masterfrom
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Prevents panic: runtime error: makeslice: cap out of range when list/sorted/enumerate receive a large range() argument. Applies the same maxAlloc=1<<30 guard already used in *Repeat helpers.
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Thanks. The code changes here look fine to me as a means to prevent accidents, but I fear this is at best a band-aid covering the most trivial ways in which it is possible to cause the interpreter to allocate too much memory. A creative adversary can easily find more complicated ways to do it, and I think it's unlikely that there will be a systematic way to avoid such problems by handling Go OOM conditions. (Even if all allocations performed by the interpreter used a different allocator, application-defined built-in functions would not.) That said, the iterable returned by |
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list(), sorted(), and enumerate() preallocate a backing slice using
Len(iterable) as the capacity with no upper-bound check. When called
with a large range() value (e.g. list(range(4611686018427387904))),
the resulting make([]Value, 0, 2^62) overflows and the Go runtime panics:
panic: runtime error: makeslice: cap out of range
go.starlark.net/starlark.list(...)
starlark/library.go:689
The panic is unrecovered and kills the host process. Any application
evaluating untrusted Starlark is affected.
The *Repeat helpers in eval.go already define and enforce maxAlloc=1<<30
for string/bytes/tuple repetition. This PR applies the same guard to
list(), sorted(), and enumerate().
Fixes: https://issuetracker.google.com/issues/499639516