netdev - Re: [PATCH iproute2] mptcp: avoid uninitialised errno usage

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Message-ID: <d9071d27-ed4d-f789-af90-8477dec82d6b@gmail.com>
Date:   Sun, 9 May 2021 17:38:04 -0600
From:   David Ahern <dsahern@...il.com>
To:     Florian Westphal <fw@...len.de>
Cc:     netdev@...r.kernel.org
Subject: Re: [PATCH iproute2] mptcp: avoid uninitialised errno usage

On 5/9/21 4:55 PM, Florian Westphal wrote:
> David Ahern <dsahern@...il.com> wrote:
>>>  	if (rtnl_talk(grth, &req.n, &answer) < 0) {
>>>  		fprintf(stderr, "Error talking to the kernel\n");
>>> +		if (errno == 0)
>>> +			errno = EOPNOTSUPP;
>>
>> you don't list the above string in the output in the commit log. Staring
>> at rtnl_talk and recvmsg and its failure paths, it seems unlikely that
>> path is causing the problem.
> 
> Its not in my particular case, but if it would caller would still get random errno.
> 
> The sketch I sent merely provides a relible errno whenever ret is less
> than 0.  Right now it may or may not have been set.
> 

Then let's find and fix those locations.

Unless I missed a code path, rtnl_talk and friends (e.g.,
__rtnl_talk_iov) all set errno before any < 0 return.