Re: qemu-sockets: account for trailing \0 byte in unix socket pathname

["Marc-André Lureau" <marcandre.lureau@redhat.com>]

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Hi

On Tue, Aug 31, 2021 at 9:17 PM Michael Tokarev <mjt@tls.msk.ru> wrote:

> 31.08.2021 01:54, Michael Tokarev wrote:
> > Linux kernel can return size of af_unix socket to be
> > one byte larger than sockaddr_un structure - adding
> > the trailing zero byte.
> >
> > Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
> > Fixes: 4cfd970ec188558daa6214f26203fe553fb1e01f (first in 6.1.0)
> > Cc: qemu-stable@nongnu.org
> >
> > diff --git a/util/qemu-sockets.c b/util/qemu-sockets.c
> > index f2f3676d1f..83926dc2bc 100644
> > --- a/util/qemu-sockets.c
> > +++ b/util/qemu-sockets.c
> > @@ -1345,8 +1345,9 @@ socket_sockaddr_to_address_unix(struct
> sockaddr_storage *sa,
> >       SocketAddress *addr;
> >       struct sockaddr_un *su = (struct sockaddr_un *)sa;
> >
> > +    /* kernel might have added \0 terminator to non-abstract socket */
> >       assert(salen >= sizeof(su->sun_family) + 1 &&
> > -           salen <= sizeof(struct sockaddr_un));
> > +           salen <= sizeof(struct sockaddr_un) + su->sun_path[0] ? 1 :
> 0);
> >
> >       addr = g_new0(SocketAddress, 1);
> >       addr->type = SOCKET_ADDRESS_TYPE_UNIX;
>
> Actually, this is not sufficient.
>
> While this change fixes one issue (the famous trailing null byte \0),
> the actual assertion failure occurs because salen = 2, ie, too SMALL,
> not too large.
>
> So it looks like libvirt provides an unnamed socket there, --
> maybe from a socketpair(2)?
>

Yes

Ok, I guess it should still check for salen >= sizeof(su->sun_family)

and then modify if (salen > sizeof(su->sun_family) && !su->sun_path[0]) {


> Hwell..
>

hmm, too bad we didn't catch it during RC!

(strange that it seems to hit Debian libvirt/virt-manager users and
apparently not on Fedora)

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