ESP32: `spi:close/1` crashes the VM with a double free

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Assessment

Difficulty
2/5
Estimated time
1-3 hours
Newbie friendliness
85/100
Issue type
Bug
Clarity
Clearly specified
Activity status
Active
Tech stack
c, erlang
Domain
embedded-iot

Research direction

Start with src/platforms/esp32/components/avm_builtins/spi_driver.c at spidriver_close, then check src/libAtomVM/context.c at context_destroy to follow the second free. Reproduce with the ESP32-C6 example in the issue; done means closing the SPI device no longer triggers the heap assertion or reboot.

Written by the indexing model from the issue text.

Description

Description

Calling spi:close/1 on an ESP32 aborts the VM with a heap assertion.

spidriver_close frees the port's platform data but leaves ctx->platform_data pointing at it:

https://github.com/atomvm/AtomVM/blob/main/src/platforms/esp32/components/avm_builtins/spi_driver.c#L337

spidriver_consume_mailbox then returns NativeTerminate, and context_destroy frees ctx->platform_data a second time:

https://github.com/atomvm/AtomVM/blob/main/src/libAtomVM/context.c#L307

To reproduce

On an ESP32-C6 running v0.7.0-beta.0, which is also present on main:

SPI = spi:open([
    {bus_config, [{mosi, 1}, {sclk, 23}, {peripheral, "spi2"}]},
    {device_config, [{leds, [{clock_speed_hz, 2500000}, {mode, 0}, {cs, -1}, {address_len_bits, 0}]}]}
]),
ok = spi:write(SPI, leds, #{write_data => <<0>>}),
spi:close(SPI).

The log shows Removed SPI device. and Stopped SPI Bus., then assert failed: 0x4002838e and a reboot.

Suggested fix

Set ctx->platform_data = NULL; after free(spi_data); in spidriver_close, so context_destroy doesn't free it again.

Dominant language
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Merged PRs (30d)
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