From mboxrd@z Thu Jan 1 00:00:00 1970 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on inbox.vuxu.org X-Spam-Level: X-Spam-Status: No, score=-3.3 required=5.0 tests=MAILING_LIST_MULTI, RCVD_IN_DNSWL_MED,RCVD_IN_MSPIKE_H3,RCVD_IN_MSPIKE_WL, T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.4 Received: (qmail 13711 invoked from network); 2 Jun 2022 14:25:21 -0000 Received: from mother.openwall.net (195.42.179.200) by inbox.vuxu.org with ESMTPUTF8; 2 Jun 2022 14:25:21 -0000 Received: (qmail 7783 invoked by uid 550); 2 Jun 2022 14:25:18 -0000 Mailing-List: contact musl-help@lists.openwall.com; run by ezmlm Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-ID: Reply-To: musl@lists.openwall.com Received: (qmail 7751 invoked from network); 2 Jun 2022 14:25:17 -0000 Date: Thu, 2 Jun 2022 10:25:05 -0400 From: Rich Felker To: Sascha Braun Cc: musl@lists.openwall.com Message-ID: <20220602142504.GY7074@brightrain.aerifal.cx> References: <20220601141453.GW7074@brightrain.aerifal.cx> <20220601213022.GX7074@brightrain.aerifal.cx> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Subject: Re: [musl] Problably Issue in name_from_dns // __res_msend_rc (lookup_name.c) On Wed, Jun 01, 2022 at 11:52:46PM +0200, Sascha Braun wrote: > I see - getaddrinfo always returns -2, EAI_NONAME in case of these rare > errors. > > The errno value (EAGAIN) came from my syscall, recvfrom, which does not > have data in these cases (all packets indicated by 'poll' were read > previously by recvfrom calls). (Btw., I did try to return 0 for these cases > in my recvfrom implementation, did not help either.) It's normal to see these EAGAINs. They are not errors. Returning 0 would be wrong; a zero-length read means EOF not EAGAIN. I don't see an immediate cause visible for why you're getting EAI_NONAME. Note that your debug output does not seem to show the *length* recvfrom returned, so is it possible you're just showing old data that was already in the buffer, when recvfrom really malfunctioned and returned a short read? At the res_msend loop layer musl would possibly accept this (like you seem to be seeing) but then find no results later. Rich > > Thanks > > Am Mi., 1. Juni 2022 um 23:30 Uhr schrieb Rich Felker : > > > On Wed, Jun 01, 2022 at 10:35:52PM +0200, Sascha Braun wrote: > > > Hi Rich, > > > > > > Thanks for your time. The EADDRINUSE is in reality an EAGAIN, this is a > > > glitch in the Emscripten/WASI modification for musl (there are different > > > values for errnos per implementation): > > > __WASI_ERRNO_ADDRINUSE == -3 == EAI_AGAIN. > > > > > > My question currently breaks down to: Is it common for this > > implementation > > > of getaddrinfo to return EAGAIN sometimes (I experience 1:100), even if > > > answers from DNS servers came in? > > > If not, I need to investigate much further. I really could not find > > issues > > > with my sockets implementation, although your thought is of course very > > > reasonable. > > > > OK, looking at your code again, part of your problem is that you're > > misusing perror. You need to save the return value of getaddrinfo. > > Unless it's EAI_SYSTEM, errno is meaningless and you need to use > > gai_strerror to get a string for the error code (the value that was > > returned) rather than inspecting errno. > > > > If getaddrinfo actually returned EAI_AGAIN, this probably means you > > got an inconclusive result from one of the nameservers, probably > > ServFail. However if your debug output is packet dumps, I'm not seeing > > a ServFail there, and I'm not convinced it actually returned EAI_AGAIN > > since you're not saving the value to check it. The value that happens > > to be in errno is NOT the error getaddrinfo returned. Can you check > > what it's actually returning? > > > > > > > Am Mi., 1. Juni 2022 um 16:14 Uhr schrieb Rich Felker : > > > > > > > On Tue, May 31, 2022 at 12:24:19PM +0200, Sascha Braun wrote: > > > > > Hi everyone, > > > > > > > > > > I'm implementing a socket protocol with similar works to Emscripten > > - ok: > > > > > > > > > > Here's what I noticed > > > > > > > > > > - resolv.conf using multiple DNS servers > > > > > options timeout:22 attempts:5 > > > > > nameserver 8.8.4.4 > > > > > nameserver 208.67.222.222 > > > > > nameserver 9.9.9.9 > > > > > nameserver 1.1.1.1 > > > > > > > > > > - getaddrinfo with no hints, so that IPV6 and IPV4 is resolved > > > > > void socketstest1_client_dnsonly(void) { > > > > > > > > > > struct addrinfo hints, * res; > > > > > memset(&hints, 0, sizeof(hints)); > > > > > printf("begin lookup1...\n"); > > > > > if (getaddrinfo("www.web.de", "80", &hints, &res) != 0) { > > > > > perror("getaddrinfo1"); > > > > > } > > > > > printf("begin lookup2...\n"); > > > > > if (getaddrinfo("www.google.de", "80", &hints, &res) != 0) { > > > > > perror("getaddrinfo2"); > > > > > } > > > > > printf("begin lookup3...\n"); > > > > > if (getaddrinfo("www.google.com", "80", &hints, &res) != 0) { > > > > > perror("getaddrinfo3"); > > > > > } > > > > > > > > > > } > > > > > > > > > > When repeating socketstest1_client_dnsonly often, it appears that > > IPV6 > > > > > answers for IPV4 requests to another server [or vice-versa] > > responses can > > > > > get mixed up and getaddrinfo reports sometimes only an error where > > none > > > > is. > > > > > > > > > > Below is a console dump of my test where you see the critical > > situation > > > > > (end) > > > > > 8.8.4.4:53 was queried, 9.9.9.9:53 responded for a (different IP > > Proto), > > > > > resulting in error getaddrinfo1: Address in use > > > > > > > > > > This happens in about 1/100 tests. When you specify IPV4 or IPV6 in > > > > hints, > > > > > this issue does NOT show up. > > > > > > > > Can you provide more information on how to interpret the console dump, > > > > and in particular, which of your syscalls is returning the EADDRINUSE > > > > error? I'm pretty sure this is just a bug in your socket > > > > stack/emulation. It looks like it's coming from recvfrom, and > > > > EADDRINUSE is not a valid error for recvfrom to produce. > > > > > > > > Rich > > > > > >