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Date: Tue, 7 Mar 2017 16:24:04 +0100 From: Alexander Potapenko <glider@...gle.com> To: Eric Dumazet <eric.dumazet@...il.com> Cc: Dmitriy Vyukov <dvyukov@...gle.com>, Kostya Serebryany <kcc@...gle.com>, Eric Dumazet <edumazet@...gle.com>, David Miller <davem@...emloft.net>, LKML <linux-kernel@...r.kernel.org>, Networking <netdev@...r.kernel.org> Subject: Re: [PATCH] net: initialize msg.msg_flags in recvfrom On Tue, Mar 7, 2017 at 3:26 PM, Eric Dumazet <eric.dumazet@...il.com> wrote: > On Tue, 2017-03-07 at 14:58 +0100, Alexander Potapenko wrote: >> 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 Google Germany GmbH Erika-Mann-Straße, 33 80636 München Geschäftsführer: Matthew Scott Sucherman, Paul Terence Manicle Registergericht und -nummer: Hamburg, HRB 86891 Sitz der Gesellschaft: Hamburg
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