From mboxrd@z Thu Jan 1 00:00:00 1970 X-Msuck: nntp://news.gmane.org/gmane.linux.lib.musl.general/9892 Path: news.gmane.org!not-for-mail From: Sebastian Gottschall Newsgroups: gmane.linux.lib.musl.general Subject: Re: recvmsg/sendmsg broken on mips64 Date: Mon, 11 Apr 2016 08:35:00 +0200 Message-ID: <278cc21f-683e-89c0-75f6-e57d9c3bd82c@dd-wrt.com> References: <20160401131712.GV9862@port70.net> <4445e7a7-19f3-aa7c-04dc-3e329ef7fdac@dd-wrt.com> <20160407094806.GE9862@port70.net> <20160407184643.GI9862@port70.net> <2656e404-f225-cd95-3989-a48df486d914@dd-wrt.com> <20160410221812.GP21636@brightrain.aerifal.cx> <20160410222947.GQ21636@brightrain.aerifal.cx> <20160411023522.GR21636@brightrain.aerifal.cx> Reply-To: musl@lists.openwall.com NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit X-Trace: ger.gmane.org 1460356511 29533 80.91.229.3 (11 Apr 2016 06:35:11 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Mon, 11 Apr 2016 06:35:11 +0000 (UTC) To: musl@lists.openwall.com Original-X-From: musl-return-9905-gllmg-musl=m.gmane.org@lists.openwall.com Mon Apr 11 08:35:08 2016 Return-path: Envelope-to: gllmg-musl@m.gmane.org Original-Received: from mother.openwall.net ([195.42.179.200]) by plane.gmane.org with smtp (Exim 4.69) (envelope-from ) id 1apVR6-0002lp-WE for gllmg-musl@m.gmane.org; Mon, 11 Apr 2016 08:35:01 +0200 Original-Received: (qmail 1845 invoked by uid 550); 11 Apr 2016 06:34:58 -0000 Mailing-List: contact musl-help@lists.openwall.com; run by ezmlm Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-ID: Original-Received: (qmail 1827 invoked from network); 11 Apr 2016 06:34:57 -0000 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=dd-wrt.com; s=mikd; h=Subject:Content-Transfer-Encoding:Content-Type:In-Reply-To:MIME-Version:Date:Message-ID:From:References:To; bh=KiJFgeuiUiYPkMn4r8MBTmzsnJ0ZnKwXcgn7j5AAkEM=; b=FMLAIrx1kz/Yy5mw38GH+FH5QX1/CQm9sxOhvXg5ZCj353sEeUGvUK35tGR5b8ZpiFWBhf1hA0qp3bMbfIBmkcofZ5oRcx94tbrif0jRSewgQeb1yQKodrTfvWnh1J5Zy+8ejOLTSoVpYgoGDgtcW4Sdpw/HbVVPd6YQwGlX8SM=; User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:45.0) Gecko/20100101 Thunderbird/45.0 In-Reply-To: <20160411023522.GR21636@brightrain.aerifal.cx> X-SA-Exim-Connect-IP: 217.234.132.69 X-SA-Exim-Mail-From: s.gottschall@dd-wrt.com X-Spam-Checker-Version: SpamAssassin 3.1.9 (2007-02-13) on webmail.newmedia-net.de X-Spam-Level: X-Spam-Status: No, score=-2.5 required=4.0 tests=ALL_TRUSTED,BAYES_00, DNS_FROM_AHBL_RHSBL,RATWARE_GECKO_BUILD autolearn=no version=3.1.9, No X-SA-Exim-Version: 4.2.1 (built Thu, 26 May 2011 15:22:33 +0200) X-SA-Exim-Scanned: Yes (on webmail.newmedia-net.de) X-NMN-MailScanner-Information: Please contact the ISP for more information X-NMN-MailScanner-ID: 1apVQq-0006TV-Lk X-NMN-MailScanner: Found to be clean X-NMN-MailScanner-From: s.gottschall@dd-wrt.com X-Received: from [217.234.132.69] (helo=[10.88.193.128]) by webmail.newmedia-net.de with esmtpsa (TLSv1:AES128-SHA:128) (Exim 4.72) (envelope-from ) id 1apVQq-0006TV-Lk for musl@lists.openwall.com; Mon, 11 Apr 2016 08:34:45 +0200 Xref: news.gmane.org gmane.linux.lib.musl.general:9892 Archived-At: Am 11.04.2016 um 04:35 schrieb Rich Felker: > On Mon, Apr 11, 2016 at 12:33:07AM +0200, Sebastian Gottschall wrote: >> Am 11.04.2016 um 00:29 schrieb Rich Felker: >>> On Mon, Apr 11, 2016 at 12:24:49AM +0200, Sebastian Gottschall wrote: >>>>> I think what nsz was asking for, and what I'd like to see, is a way to >>>>> reproduce the bug. I'm going to try building iproute2 for mips64 and >>>>> running it on a prebuilt kernel from Aboriginal Linux under >>>>> qemu-system-mips64, but I don't know what specific commands are needed >>>>> to hit the affected code path. >>>> any command since all is netlink based >>>> ip add add 192.168.1.1/24 dev eth0 >>>> >>>> yo will see that nothing will happen. ip will just return a error >>>> message (i wrote this message already in the first entry on this >>>> mailinglist) >>>> "EOF on netlink" is the error which is shown >>> OK, I'll try this. >>> >>>>>> its all resulting in the same failing recvmsg / sendmsg call.. so >>>>>> yes libnetlink.c does not work with musl on mips64 (it does work on >>>>>> x64 and everything else, just not mips64) unless the hack i offered >>>>>> was applied which again fixed all. >>>>>> before you ask again for a problem description, just read again. it >>>>>> wont change the description if you ask again and just makes people >>>>>> tired on this list. >>>>> Both versions of the struct (musl's and your modified one that matches >>>>> the kernel) have the exact same layout, but due to having a member >>>>> with 64-bit type, yours has 8-byte alignment and musl's only has >>>>> 4-byte alignment. This means, at least: >>>>> >>>>> 1. When musl's sendmsg.c makes its copy to zero out the padding, the >>>>> copy may not be correctly aligned for 64-bit writes, and the kernel >>>>> faults or manually produces an error for this case, causing the >>>>> whole operation to fail. However, I don't see where iproute2 is >>>>> actually passing control messages to sendmsg, so while this is a >>>>> problem, I don't think it's the cause. Maybe I'm missing the >>>>> affected call point; this is why I'd like steps to reproduce the >>>>> issue so I can see it. >>>>> >>>>> 2. iproute2's libnetlink.c's rtnl_listen function does not properly >>>>> declare its cmsgbuf with the alignment of cmsghdr; it has type >>>>> char[] so the compiler is free not to align it at all. This is >>>>> presumably a bug in iproute2, but I can't find any good >>>>> documentation (in the standards or Linux-specific) for how you're >>>>> supposed to allocate this space, so maybe the kernel is able to >>>>> handle aligning the buffer itself. I don't see any way the >>>>> alignment of musl's cmsghdr type affects recvmsg though. >>>>> >>>>> Maybe there are other effects I'm missing? I'll follow up again once I >>>>> get a test build/run of iproute2 and let you know whether I can see >>>>> the problem. >>>> okay. if you need a remote access to a octeon system using musl (my >>>> fixed variant), just tell me. >>> That would be really helpful. Something's wrong with the userspace for >>> the Aboriginal mips64 binaries (SIGBUS in init) and debugging that >>> would be a big distraction. >>> >>> BTW do you have gdb and strace available? >> not on the system itself. i'm not sure if strace works on mips64. >> never tried it. >> but you're free to copy any binary to the /tmp dir. it has 2 gb ram. >> so enough space for static binaries if you want to play with. >> i will send you the ssh data in a private email > I haven't been able to reproduce the error on your system. I've tried > building my own static-linked version of the "ip" utility with a > mips64-linux-musl softfloat compiler, and uploading my libc.so and > using it to run both your version of ip and a dynamic-linked one I > just built. They all work fine for adding/removing a 127.0.0.2 address > to the "lo" interface. i can install a broken musl libc again if that helps. (its plain openwrt toolchain result) > > Next I'm going to try to get a minimal testcase that tries to > intentionally misalign the control message buffers. I suspect I'm just > "getting lucky" and my buffer happens to be aligned the way the kernel > wants by chance. > > Rich >