Fix fatal runtime panic passing invalid pointer #40
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The last argument to hs_scan is "void*", a pointer to an abitrary context. "hsScan" incorrectly uses "unsafe.Pointer(h)" when h is not a pointer. This can cause fatal runtime panic when Go passes arguments across the Go <-> C boundaries. This does not happen all the time, as it usually "looks" like a pointer. In reality, h is an unsigned long value belonging to "handles". We can coerce this into "void*" on the C side with the added "safe_hs_scan"
adonovan
reviewed
Nov 17, 2021
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See golang/go#49633, which suggests a much simpler solution of passing the address of the cgo.Handle through the C code. |
adonovan
reviewed
Nov 18, 2021
| @@ -1013,7 +1009,8 @@ type hsMatchEventContext struct { | |||
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| //export hsMatchEventCallback | |||
| func hsMatchEventCallback(id C.uint, from, to C.ulonglong, flags C.uint, data unsafe.Pointer) C.int { | |||
| ctx, ok := handle.Handle(data).Value().(hsMatchEventContext) | |||
| h := (*handle.Handle)(data) | |||
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*(*handle.Handle)(data)
The current code is not wrong because of the implicit dereference in h.Value, but h should be a Handle, not a pointer to one.
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Well, this is indeed an unthought of problem, thank you very much for your hard work :) |
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The last argument to hs_scan is "void*", a pointer to an abitrary
context. "hsScan" incorrectly uses "unsafe.Pointer(h)" when h is not a
pointer. This can cause fatal runtime error when Go passes arguments
across the Go <-> C boundaries. The runtime error does not happen all
the time, as it usually "looks" like a pointer. This makes it difficult
to reproduce.
We can fix this by actually passing a real pointer (of our
cgo.Handle)and dereferencing the pointer within the callback. I did a quick audit,
and think I updated all places where we use the callback.
I did not audit other parts of the API spec that take in a
void*arg.Thanks @adonovan for helping with most of the analysis.
Below is a small snippet of the fatal runtime panic: