Date: Thu, 10 Aug 2000 12:39:03 -0700 (PDT) From: David Wolfskill <dhw@whistle.com> To: FreeBSD-gnats-submit@freebsd.org Cc: ambrisko@whistle.com, archie@whistle.com Subject: bin/20525: Trailing NUL from DHCP server makes dhclient break resolv.conf Message-ID: <200008101939.MAA21273@pau-amma.whistle.com>
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>Number: 20525 >Category: bin >Synopsis: Trailing NUL from DHCP server makes dhclient break resolv.conf >Confidential: no >Severity: serious >Priority: medium >Responsible: freebsd-bugs >State: open >Quarter: >Keywords: >Date-Required: >Class: change-request >Submitter-Id: current-users >Arrival-Date: Thu Aug 10 12:40:00 PDT 2000 >Closed-Date: >Last-Modified: >Originator: David Wolfskill >Release: FreeBSD 4.1-STABLE i386 >Organization: Whistle Communications >Environment: Running FreeBSD as a DHCP client, where the DHCP server in question has been set up to provide a trailing NUL in the supplied domain name (for broken DHCP clients that treat the domain name as a "C string"). >Description: What happens is that the domain name supplied by the server is copied into /etc/resolve.conf, but the trailing NUL is *also* "copied" -- but represented as "\000". (For example, one might see search whistle.com\000 in /etc/resolv.conf.) This causes just about anything that requires a proper domain name on the DHCP client machine to fail rather miserably. >How-To-Repeat: Well, you need such a broken/misfeatured DHCP server, first. Unfortunately, the DHCP server supplied in the Whistle InterJet is one such: Archie was the one who pointed out that the server had been modified to support certain Microsoft clients (which he identified, but I failed to keep a copy of that note) that would otherwise break. Once that's done, just fire up a FreeBSD box as a DHCP client. (Note: It is *not* fair to hand-edit /etc/resolve.conf, and then issue "chflags schg /etc/resolv.conf". This is considered un-sporting in the extreme; it's one of the ways I circumvent the problem....) After the multi-user boot finishes, take a look at /etc/resolv.conf. >Fix: Skipping the above-referenced hack, here's what Doug Ambrisko suggested in response to my comment that perhaps dhclient ought to be a little more tolerant of what it receives: From: Doug Ambrisko <ambrisko@whistle.com> Message-Id: <200007271838.LAA42370@whistle.com> Subject: Re: 4.1-RC heads up on dhclient To: David Wolfskill <dhw@whistle.com> Date: Thu, 27 Jul 2000 11:38:39 -0700 (PDT) David Wolfskill writes: | Perhaps the dhclient should be fixed to be a bit more tolerant -- possibly | in addition to anything else. After all, I'd not expect a NUL to be a | valid character in a domain name.... :-} Here it is, feel free to submit this on my behalf. I've tried it against alpo and a good dhcp server and it appears to work. Doug A. Index: common/options.c =================================================================== RCS file: /cvs/freebsd/src/contrib/isc-dhcp/common/options.c,v retrieving revision 1.1.1.3.2.1 diff -c -r1.1.1.3.2.1 options.c *** options.c 2000/06/26 23:07:21 1.1.1.3.2.1 --- options.c 2000/07/27 18:37:23 *************** *** 492,497 **** --- 492,499 ---- fmtbuf [i] = 't'; fmtbuf [i + 1] = 0; numhunk = -2; + /* accept null-terminated string */ + if(len && !dp[len-1]) len--; break; case 'I': case 'l': In reviewing that, it occurred to me that the above could still break if there were multiple trailing NULs. Granted, that's pathological, but this would fix that, I think (though I haven't tested it): Index: common/options.c =================================================================== RCS file: /cvs/freebsd/src/contrib/isc-dhcp/common/options.c,v retrieving revision 1.1.1.3.2.1 diff -c -r1.1.1.3.2.1 options.c *** options.c 2000/06/26 23:07:21 1.1.1.3.2.1 --- options.c 2000/07/27 18:37:23 *************** *** 492,497 **** --- 492,499 ---- fmtbuf [i] = 't'; fmtbuf [i + 1] = 0; numhunk = -2; + /* accept null-terminated string */ + while (len && !dp[len-1]) len--; break; case 'I': case 'l': All that aside, it would probably be better to scan from the left side of the domain name, and stop if either "len" is reached or a character is read that is invalid in a domain name. >Release-Note: >Audit-Trail: >Unformatted: To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-bugs" in the body of the message
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