[release/5.0] [mono] Copy image data with AssemblyLoadContext.LoadFromStream#43593
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lewing merged 1 commit intorelease/5.0from Oct 20, 2020
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[release/5.0] [mono] Copy image data with AssemblyLoadContext.LoadFromStream#43593lewing merged 1 commit intorelease/5.0from
lewing merged 1 commit intorelease/5.0from
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We don't actually pin the byte array, so it must be copied or it can be overwritten once we run a GC on the LOH. Fixes #43402 Tested manually that it fixes the issue using the associated repro. This isn't really something that lends itself to a test, so that's the best I can do.
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Backport of #43592 to release/5.0
/cc @CoffeeFlux
Customer Impact
Fix was prompted by a customer bug report at #43402
This bug will affect anyone using AssemblyLoadContext.LoadFromStream on wasm with enough other data in the LOH to trigger a GC, so the potential for others to hit this seems high in real applications despite it not showing up in testing.
Testing
Manually validated against the attached repro. Problem goes away even after 10 iterations, when previously the corruption would be evident on the first.
Risk
Low. This is just a one-line change that ensure we copy the data locally into non-managed memory. The copying functionality is hit regularly multiple other places in the runtime in addition to being fairly simple, so it is unlikely to cause problems. In a .NET 5 context, this fix is wasm-specific.