Daniel Borkmann <dan...@iogearbox.net> [Thu, 2018-05-24 18:00 -0700]:
> On 05/23/2018 01:40 AM, Andrey Ignatov wrote:
> [...]
> > diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
> > index ff4d4ba..a1f9ba2 100644
> > --- a/net/ipv4/udp.c
> > +++ b/net/ipv4/udp.c
> > @@ -900,6 +900,7 @@ int udp_sendmsg(struct sock *sk, struct msghdr *msg,
> > size_t len)
> > {
> > struct inet_sock *inet = inet_sk(sk);
> > struct udp_sock *up = udp_sk(sk);
> > + DECLARE_SOCKADDR(struct sockaddr_in *, usin, msg->msg_name);
> > struct flowi4 fl4_stack;
> > struct flowi4 *fl4;
> > int ulen = len;
> > @@ -954,8 +955,7 @@ int udp_sendmsg(struct sock *sk, struct msghdr *msg,
> > size_t len)
> > /*
> > * Get and verify the address.
> > */
> > - if (msg->msg_name) {
> > - DECLARE_SOCKADDR(struct sockaddr_in *, usin, msg->msg_name);
> > + if (usin) {
> > if (msg->msg_namelen < sizeof(*usin))
> > return -EINVAL;
> > if (usin->sin_family != AF_INET) {
> > @@ -1009,6 +1009,22 @@ int udp_sendmsg(struct sock *sk, struct msghdr *msg,
> > size_t len)
> > rcu_read_unlock();
> > }
> >
> > + if (!connected) {
> > + err = BPF_CGROUP_RUN_PROG_UDP4_SENDMSG_LOCK(sk,
> > + (struct sockaddr *)usin, &ipc.addr);
> > + if (err)
> > + goto out_free;
> > + if (usin) {
> > + if (usin->sin_port == 0) {
> > + /* BPF program set invalid port. Reject it. */
> > + err = -EINVAL;
> > + goto out_free;
> > + }
> > + daddr = usin->sin_addr.s_addr;
> > + dport = usin->sin_port;
> > + }
> > + }
> > +
> > saddr = ipc.addr;
> > ipc.addr = faddr = daddr;
> >
> > diff --git a/net/ipv6/udp.c b/net/ipv6/udp.c
> > index 2839c1b..67c44b5 100644
> > --- a/net/ipv6/udp.c
> > +++ b/net/ipv6/udp.c
> > @@ -1315,6 +1315,29 @@ int udpv6_sendmsg(struct sock *sk, struct msghdr
> > *msg, size_t len)
> > fl6.saddr = np->saddr;
> > fl6.fl6_sport = inet->inet_sport;
> >
> > + if (!connected) {
> > + err = BPF_CGROUP_RUN_PROG_UDP6_SENDMSG_LOCK(sk,
> > + (struct sockaddr *)sin6, &fl6.saddr);
> > + if (err)
> > + goto out_no_dst;
> > + if (sin6) {
> > + if (ipv6_addr_v4mapped(&sin6->sin6_addr)) {
> > + /* BPF program rewrote IPv6-only by IPv4-mapped
> > + * IPv6. It's currently unsupported.
> > + */
> > + err = -ENOTSUPP;
> > + goto out_no_dst;
> > + }
> > + if (sin6->sin6_port == 0) {
> > + /* BPF program set invalid port. Reject it. */
> > + err = -EINVAL;
> > + goto out_no_dst;
> > + }
> > + fl6.fl6_dport = sin6->sin6_port;
> > + fl6.daddr = sin6->sin6_addr;
> > + }
>
> Hmm, this extra work here and in v4 case should probably all be done under
> the static key? Otherwise we'll do the extra work for checking sin6 and
> setting up fl6 twice?
Hm .. true, we can put the whole this block under static key (the main
one, since there are no others, but we can follow-up separately):
if (cgroup_bpf_enabled && !connected) {
I'll send v3 with this change for both ipv6 and ipv4. Thanks.
As for the logic inside the `if`, I'll describe it just in case, since
some things may not be obvious.
There are two cases earlier in this function that can lead to
`connected = false`, either user specifies destination address (the 1st
`if (sin6)`) or/and user specifies ancillary data
(`if (msg->msg_controllen)`).
Ancillary data can contain option to set source IP. So to simplify: if
user specifies source or destination we're in unconnected mode.
Now imagine that we have connected socket and then user calls sendmsg
without setting destination (sin6 = NULL), but sets the source IP in
ancillary data at the same time. It will cause `connected = false` and
BPF prog will be run (it can e.g. override that source IP set by user),
but we have no sin6, that's why this `if (sin6)` is second time here.
On the other hand if sin6 is passed by user, it'll cause unconnected
mode as well and BPF prog has a chance to override IP and port in sin6
and in this case we have to update fl6 after BPF prog finishes. That's
why `fl6.daddr = sin6->sin6_addr;` the second time.
But I agree that work should be avoided when cgroup-bpf is disabled.
> Also, when not enabled, couldn't we run into the case
> of ipv6_addr_v4mapped() as well? If I'm spotting this right, then we would
> bail out though we shouldn't normally?
IPv4-mapped IPv6 case is handled earlier in this function and if user
passed IPv4-mapped IPv6, we don't get this far and call IPv4
udp_sendmsg() much earlier.
Same is true for port.
That's why this code wouldn't affect the logic for IPv4-mapped IPv6, but
again, you're right that we shouldn't do this extra work when cgroup-bpf
is disabled and I'll fix it.
>
> > + }
> > +
> > final_p = fl6_update_dst(&fl6, opt, &final);
> > if (final_p)
> > connected = false;
> > @@ -1394,6 +1417,7 @@ int udpv6_sendmsg(struct sock *sk, struct msghdr
> > *msg, size_t len)
> >
> > out:
> > dst_release(dst);
> > +out_no_dst:
> > fl6_sock_release(flowlabel);
> > txopt_put(opt_to_free);
> > if (!err)
> >
>
--
Andrey Ignatov
