lwm2m_engine: Error when enabling debug log because of uninitialized variable `from_addr`

[petterssonandreas]

Describe the bug There is an uninitialized variable from_addr in function socket_recv_message in lwm2m_engine.c, which is the cause of the following error:

[00:07:53.415,954] <err> net_lwm2m_engine: Unknown IP address family:0
[00:07:53.416,015] <dbg> net_lwm2m_engine: lwm2m_udp_receive: checking for reply from [unk]

This error only occurs when debug logs are enabled, since the error is actually produced in a function called as an argument to a LOG_DBG.

The code in question: https://github.com/zephyrproject-rtos/zephyr/blob/e83b0741285416fe356eb2d5d0002dddf56a893f/subsys/net/lib/lwm2m/lwm2m_engine.c#L4530-L4562

from_addr is never given a value, which will most likely mean that from_addr.sa_family will be 0, meaning "Unknown IP address family". Unless I have misunderstood what recvfrom does, and if that could write to from_addr?

To Reproduce Enable LWM2M logs on DBG level, by setting CONFIG_LWM2M_LOG_LEVEL_DBG=y in your prj.conf. Run some code using the lwm2m_rd_client, then the error should pop up in the logs.

Expected behavior No error produced. The variable should be initialized.

One way to achieve a correct address is in my case to add:

memcpy(&from_addr, &client_ctx->remote_addr, sizeof(from_addr));

Is this a good solution? (I'm not sure if remote_addr is always populated)

Impact Only annoying, no impact on functionality.

Environment (please complete the following information):

• OS: Ubuntu 20.04
• Toolchain: gnuarmemb
• Tested on v2.7.0-ncs1 but found no fix on latest main either

[rlubos]

Hi @petterssonandreas,

Since you're referring to NCS, I'm assuming you're using nRF91 modem? There is a known issue, that the offloaded recvfrom() does not set the address field when using DTLS.

In general, recvfrom() should fill the address buffers when it reports new data, there's no need for the address buffers to be initialized. The proposed solution is more of a workaround for a faulty underlying recvfrom() implmentation, I'd rather avoid that in the LwM2M code.

As the nRF91 socket implementation is not a part of Zephyr, but NCS only, it's not really a Zephyr issue - please file a devzone ticket instead.

[petterssonandreas]

Hi @rlubos,

Yes, I'm using the nRF91 modem. Oh, okay, then I understand. I am not too familiar with sockets so was hard for me to find the correct documentation for it.

But, yes, in that case I agree that my "solution" is incorrect. I will post a ticket at Devzone instead.

Thanks for the input! I will close this issue.

[petterssonandreas]

Just as an FYI if anyone else finds this issue, I have opened a ticket on Devzone that you can check out if you are interested: https://devzone.nordicsemi.com/f/nordic-q-a/84271/socket-recvfrom-doesn-t-fill-out-address-buffer