downlink: fix double free when block queue is full - #140
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When we are unable to allocate a downlink block, we close the downlink and return an error to the CoAP client. But returning an error to the CoAP client also eventually results in closing the downlink. Closing the downlink involves flushing the block queue and releasing the currently held block, and doing it twice leads to a double free of the currently held block. To fix, we do not close the downlink directly when we are unable to allocate a block, instead we just return an error to the CoAP client. Signed-off-by: Sam Friedman <sam@golioth.io>
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szczys and
trond-snekvik
February 20, 2026 05:00
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When we are unable to allocate a downlink block, we close the downlink and return an error to the CoAP client. But returning an error to the CoAP client also eventually results in closing the downlink. Closing the downlink involves flushing the block queue and releasing the currently held block, and doing it twice leads to a double free of the currently held block. To fix, we do not close the downlink directly when we are unable to allocate a block, instead we just return an error to the CoAP client.
This bug was introduced in #137 which added the proper handling for errors in CoAP callbacks during downlink.