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Re: [Qemu-devel] [PATCH v3] slirp: fix ICMP handling on macOS hosts
From: |
Andrew Oates |
Subject: |
Re: [Qemu-devel] [PATCH v3] slirp: fix ICMP handling on macOS hosts |
Date: |
Wed, 15 Aug 2018 10:00:55 -0400 |
On Wed, Aug 15, 2018 at 7:03 AM Samuel Thibault <address@hidden>
wrote:
> Andrew Oates, le mar. 14 août 2018 22:35:21 -0400, a ecrit:
> > On Linux, SOCK_DGRAM+IPPROTO_ICMP sockets give only the ICMP packet when
> > read from. On macOS, however, the socket acts like a SOCK_RAW socket
> > and includes the IP header as well.
> >
> > This change strips the extra IP header from the received packet on macOS
> > before sending it to the guest. SOCK_DGRAM ICMP sockets aren't
> > supported on other BSDs, but we enable this behavior for them as well to
> > treat the sockets the same as raw sockets.
> >
> > Signed-off-by: Andrew Oates <address@hidden>
> > ---
> > v2: check validity of inner_hlen and update len appropriately
> > v3: CONFIG_DARWIN -> CONFIG_BSD; add comment explaining #ifdef
> >
> > slirp/ip_icmp.c | 24 +++++++++++++++++++++++-
> > 1 file changed, 23 insertions(+), 1 deletion(-)
> >
> > diff --git a/slirp/ip_icmp.c b/slirp/ip_icmp.c
> > index 0b667a429a..0e289fd9d9 100644
> > --- a/slirp/ip_icmp.c
> > +++ b/slirp/ip_icmp.c
> > @@ -420,7 +420,29 @@ void icmp_receive(struct socket *so)
> > icp = mtod(m, struct icmp *);
> >
> > id = icp->icmp_id;
> > - len = qemu_recv(so->s, icp, m->m_len, 0);
> > + len = qemu_recv(so->s, icp, M_ROOM(m), 0);
> > + /*
> > + * The behavior of reading SOCK_DGRAM+IPPROTO_ICMP sockets is
> inconsistent
> > + * between host OSes. On Linux, only the ICMP header and payload is
> > + * included. On macOS/Darwin, the socket acts like a raw socket and
> > + * includes the IP header as well. On other BSDs,
> SOCK_DGRAM+IPPROTO_ICMP
> > + * sockets aren't supported at all, so we treat them like raw
> sockets. It
> > + * isn't possible to detect this difference at runtime, so we must
> use an
> > + * #ifdef to determine if we need to remove the IP header.
> > + */
> > +#ifdef CONFIG_BSD
> > + if (len > 0) {
>
> Looking at it again, this used to be
>
> if (len >= sizeof(struct ip)) {
>
> shouldn't be it that way so that
>
> > + struct ip *inner_ip = mtod(m, struct ip *);
> > + int inner_hlen = inner_ip->ip_hl << 2;
>
> Reading in the header doesn't give uninitialized values?
>
> I guess that to be on the safe side and trigger explicit warnings, we
> should reject with EINVAL packets which are smaller than an IP header?
>
Hmm, yeah, sorry. That got reverted in my patch and I didn't notice. Will
re-send.
>
> > + if (inner_hlen > len) {
> > + len = -1;
> > + errno = -EINVAL;
> > + } else {
> > + len -= inner_hlen;
> > + memmove(icp, (unsigned char *)icp + inner_hlen, len);
> > + }
> > + }
> > +#endif
> > icp->icmp_id = id;
> >
> > m->m_data -= hlen;
> > --
> > 2.18.0.865.gffc8e1a3cd6-goog
> >
>
> --
> Samuel
> <N> (* If you have a precise idea of the intended use of the following
> code, please
> <N> write to address@hidden and ask for the prize :-)
> <N> -- Eduardo (11/8/97) *)
> -+- N sur #ens-mim - et c'était un des développeurs -+-
>