On Mon, Apr 16, 2018 at 08:13:42PM +0200, Markus Armbruster wrote: > Daniel P. Berrangé <berra...@redhat.com> writes: > > > On Mon, Apr 16, 2018 at 06:30:45PM +0200, Markus Armbruster wrote: > >> Daniel P. Berrangé <berra...@redhat.com> writes: > >> > >> > A user trying out SMBIOS "OEM strings" feature reported that the data > >> > they are exposing to the guest was truncated at 1023 bytes, which breaks > >> > 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 limits > >> > 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. > >> > >> Too bad I haven't been able to complete my quest to kill QemuOpts. > >> > >> 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.
Agreed, if only fragments are limited, that's fine because we know that no code ever declares a key long enough to exceed the individual fragment size. Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|