From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:53769) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1f88db-00058P-RO for qemu-devel@nongnu.org; Mon, 16 Apr 2018 14:14:00 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1f88dY-0000bW-NA for qemu-devel@nongnu.org; Mon, 16 Apr 2018 14:13:59 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:52014 helo=mx1.redhat.com) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1f88dY-0000b0-HZ for qemu-devel@nongnu.org; Mon, 16 Apr 2018 14:13:56 -0400 From: Markus Armbruster References: <20180416111743.8473-1-berrange@redhat.com> <87muy3m7uy.fsf@dusky.pond.sub.org> <20180416163839.GC17600@redhat.com> Date: Mon, 16 Apr 2018 20:13:42 +0200 In-Reply-To: <20180416163839.GC17600@redhat.com> ("Daniel P. =?utf-8?Q?Ber?= =?utf-8?Q?rang=C3=A9=22's?= message of "Mon, 16 Apr 2018 17:38:39 +0100") Message-ID: <87lgdnkoix.fsf@dusky.pond.sub.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Subject: Re: [Qemu-devel] [PATCH 0/3] Remove artificial length limits when parsing options List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "Daniel P. =?utf-8?Q?Berrang=C3=A9?=" Cc: Eduardo Habkost , "Michael S. Tsirkin" , qemu-devel@nongnu.org, Marcel Apfelbaum , Paolo Bonzini , Richard Henderson Daniel P. Berrang=C3=A9 writes: > On Mon, Apr 16, 2018 at 06:30:45PM +0200, Markus Armbruster wrote: >> Daniel P. Berrang=C3=A9 writes: >>=20 >> > A user trying out SMBIOS "OEM strings" feature reported that the data >> > they are exposing to the guest was truncated at 1023 bytes, which brea= ks >> > the app consuming in the guest. After searching for the cause I >> > eventually found that the QemuOpts parsing is using fixed length 1024 >> > byte array for option values and 128 byte array for key names. >> > >> > We can certainly debate whether it is sane to have such long command >> > line argument values (it is not sane), but if the OS was capable of >> > exec'ing QEMU with such an ARGV array, there is little good reason for >> > imposing an artificial length restriction when parsing it. Even worse = is >> > that we silently truncate without reporting an error when hitting limi= ts >> > resulting in a semantically incorrect behaviour, possibly even leading >> > to security flaws depending on the data that was truncated. >> > >> > Thus this patch series removes the artificial length limits by killing >> > the fixed length buffers. >> > >> > Separately I intend to make it possible to read "OEM strings" data from >> > a file, to avoid need to have long command line args. >>=20 >> Too bad I haven't been able to complete my quest to kill QemuOpts. >>=20 >> As far as I know, keyval.c's only arbitrary limit is the length of a key >> fragment (the things separated by '.'). > > Looks like that's the same scenario I tried to address in patch 2. The > 'key' part in QemuOpts has the same 128 byte limit as in the keyval.c > code. I fear that could be hit with -blockdev when setting params on > very deeply nested block backends. On the plus side keyval.c actually > reports an error when it hits its 128 byte limit, instead of silently > carrying on as if all was well like QemuOpts did :-) In keyval.c, the key (things like "a.b.c") can be arbitrarily long (well, until g_malloc() throws in the towel), but each key fragment ("a", "b" and "c") is limited to 128 bytes. If key length was limited there, I would've asked you to fix it there, too.