Re: [PATCH] net: initialize msg.msg_flags in recvfrom

On Tue, Mar 7, 2017 at 3:26 PM, Eric Dumazet [off-list ref] wrote:

On Tue, 2017-03-07 at 14:58 +0100, Alexander Potapenko wrote:

quoted

KMSAN (KernelMemorySanitizer, a new error detection tool) reports use
of uninitialized memory in put_cmsg()):

I would prefer that you do not put the stack trace in the changelog,
same for the reproducer since this has little value in understanding the
impact.

Understood.
Should be ok to put the report/reproducer below the triple dash, right?

It looks like a false positive, but you do not say.

Ah, now I see.
Irrespective of the value of (MSG_CMSG_COMPAT & msg->msg_flags) the
code will return 0 either directly from put_cmsg(), or from
put_cmsg_compat().
I wouldn't call this a false positive, as KMSAN can't possibly know
that both branches taken depending on the uninitialized condition are
safe.
But I can imagine this to be less of an problem to the code owners who
do know that :)

recvmsg() does not care about msg.msg_flags, only KMSAN.

(The important part is that msg.msg_control and msg.msg_controllen are
0)

Fine to avoid the false positive, but better be explicit in the
changelog and says there is no visible effect for this bug.

Ok, I'll change the description.

If there is a visible effect, please state so instead of technical
details.

We try to reduce S/N in the changelogs ;)

Thanks a lot !

-- 
Alexander Potapenko
Software Engineer

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