Re: [PATCH net v2 1/2] udp: check encap socket in __udp_lib_err_encap

On 17.07.2021 19:41, Xin Long wrote:

On Fri, Jul 16, 2021 at 6:32 PM Vadim Fedorenko [off-list ref] wrote:

quoted

On 16.07.2021 19:46, Xin Long wrote:

quoted

On Fri, Jul 16, 2021 at 6:54 AM Vadim Fedorenko [off-list ref] wrote:

quoted

Commit d26796ae5894 ("udp: check udp sock encap_type in __udp_lib_err")
added checks for encapsulated sockets but it broke cases when there is
no implementation of encap_err_lookup for encapsulation, i.e. ESP in
UDP encapsulation. Fix it by calling encap_err_lookup only if socket
implements this method otherwise treat it as legal socket.

Fixes: d26796ae5894 ("udp: check udp sock encap_type in __udp_lib_err")
Signed-off-by: Vadim Fedorenko <redacted>
---
   net/ipv4/udp.c | 23 +++++++++++++++++------
   net/ipv6/udp.c | 23 +++++++++++++++++------
   2 files changed, 34 insertions(+), 12 deletions(-)

diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index 62cd4cd52e84..963275b94f00 100644
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c

@@ -645,10 +645,12 @@ static struct sock *__udp4_lib_err_encap(struct net *net,
                                           const struct iphdr *iph,
                                           struct udphdr *uh,
                                           struct udp_table *udptable,
+                                        struct sock *sk,
                                           struct sk_buff *skb, u32 info)
   {
+       int (*lookup)(struct sock *sk, struct sk_buff *skb);
          int network_offset, transport_offset;
-       struct sock *sk;
+       struct udp_sock *up;

          network_offset = skb_network_offset(skb);
          transport_offset = skb_transport_offset(skb);

@@ -659,12 +661,19 @@ static struct sock *__udp4_lib_err_encap(struct net *net,
          /* Transport header needs to point to the UDP header */
          skb_set_transport_header(skb, iph->ihl << 2);

+       if (sk) {
+               up = udp_sk(sk);
+
+               lookup = READ_ONCE(up->encap_err_lookup);
+               if (!lookup || !lookup(sk, skb))
+                       goto out;
+       }
+

Currently SCTP reuses lookup() to handle some of ICMP error packets by itself
in lookup(), for these packets it will return 1, in which case we should
set sk = NULL, and not let udp4_lib_err() handle these packets again.

Can you change this part to this below?

+       if (sk) {
+               up = udp_sk(sk);
+
+               lookup = READ_ONCE(up->encap_err_lookup);
+               if (lookup && lookup(sk, skb))
+                       sk = NULL;
+
+               goto out;
+       }
+

thanks.

But we have vxlan and geneve with encap_err_lookup handler enabled and which do
not handle ICMP itself, just checks whether socket is correctly selected. Such
code could break their implementation

Sorry, I don't see how this will break vxlan and geneve implementation.

It checking 'sk' and calling lookup() here means we believe this sk
should be the correct one (for the case of src == dst port only). So
even if lookup() returns !0, we should NOT go to another
__udp4_lib_lookup() in __udp4_lib_err_encap().

If we don't believe this sk should be the correct one, as the sk was
found with reverse ports, then we should NOT call lookup() with this sk
but call __udp4_lib_lookup() directly in __udp4_lib_err_encap(), as it
currently does, and fix this by checking READ_ONCE(up->encap_err_lookup)
in __udp4_lib_lookup(), as Paolo suggested.

Either way is fine to me, but not this one. what do you think?

Thanks.

Ok, I got your point, will send v3 soon with what you suggested first.
Thanks for review!

quoted

quoted

quoted

          sk = __udp4_lib_lookup(net, iph->daddr, uh->source,
                                 iph->saddr, uh->dest, skb->dev->ifindex, 0,
                                 udptable, NULL);
          if (sk) {
-               int (*lookup)(struct sock *sk, struct sk_buff *skb);
-               struct udp_sock *up = udp_sk(sk);
+               up = udp_sk(sk);

                  lookup = READ_ONCE(up->encap_err_lookup);
                  if (!lookup || lookup(sk, skb))

@@ -674,6 +683,7 @@ static struct sock *__udp4_lib_err_encap(struct net *net,
          if (!sk)
                  sk = ERR_PTR(__udp4_lib_err_encap_no_sk(skb, info));

+out:
          skb_set_transport_header(skb, transport_offset);
          skb_set_network_header(skb, network_offset);

@@ -707,15 +717,16 @@ int __udp4_lib_err(struct sk_buff *skb, u32 info, struct udp_table *udptable)
          sk = __udp4_lib_lookup(net, iph->daddr, uh->dest,
                                 iph->saddr, uh->source, skb->dev->ifindex,
                                 inet_sdif(skb), udptable, NULL);
+
          if (!sk || udp_sk(sk)->encap_type) {
                  /* No socket for error: try tunnels before discarding */
-               sk = ERR_PTR(-ENOENT);
                  if (static_branch_unlikely(&udp_encap_needed_key)) {
-                       sk = __udp4_lib_err_encap(net, iph, uh, udptable, skb,
+                       sk = __udp4_lib_err_encap(net, iph, uh, udptable, sk, skb,
                                                    info);
                          if (!sk)
                                  return 0;
-               }
+               } else
+                       sk = ERR_PTR(-ENOENT);

                  if (IS_ERR(sk)) {
                          __ICMP_INC_STATS(net, ICMP_MIB_INERRORS);

diff --git a/net/ipv6/udp.c b/net/ipv6/udp.c
index 0cc7ba531b34..0210ec93d21d 100644
--- a/net/ipv6/udp.c
+++ b/net/ipv6/udp.c

@@ -502,12 +502,14 @@ static struct sock *__udp6_lib_err_encap(struct net *net,
                                           const struct ipv6hdr *hdr, int offset,
                                           struct udphdr *uh,
                                           struct udp_table *udptable,
+                                        struct sock *sk,
                                           struct sk_buff *skb,
                                           struct inet6_skb_parm *opt,
                                           u8 type, u8 code, __be32 info)
   {
+       int (*lookup)(struct sock *sk, struct sk_buff *skb);
          int network_offset, transport_offset;
-       struct sock *sk;
+       struct udp_sock *up;

          network_offset = skb_network_offset(skb);
          transport_offset = skb_transport_offset(skb);

@@ -518,12 +520,19 @@ static struct sock *__udp6_lib_err_encap(struct net *net,
          /* Transport header needs to point to the UDP header */
          skb_set_transport_header(skb, offset);

+       if (sk) {
+               up = udp_sk(sk);
+
+               lookup = READ_ONCE(up->encap_err_lookup);
+               if (!lookup || !lookup(sk, skb))
+                       goto out;
+       }
+
          sk = __udp6_lib_lookup(net, &hdr->daddr, uh->source,
                                 &hdr->saddr, uh->dest,
                                 inet6_iif(skb), 0, udptable, skb);
          if (sk) {
-               int (*lookup)(struct sock *sk, struct sk_buff *skb);
-               struct udp_sock *up = udp_sk(sk);
+               up = udp_sk(sk);

                  lookup = READ_ONCE(up->encap_err_lookup);
                  if (!lookup || lookup(sk, skb))

@@ -535,6 +544,7 @@ static struct sock *__udp6_lib_err_encap(struct net *net,
                                                          offset, info));
          }

+out:
          skb_set_transport_header(skb, transport_offset);
          skb_set_network_header(skb, network_offset);

@@ -558,16 +568,17 @@ int __udp6_lib_err(struct sk_buff *skb, struct inet6_skb_parm *opt,

          sk = __udp6_lib_lookup(net, daddr, uh->dest, saddr, uh->source,
                                 inet6_iif(skb), inet6_sdif(skb), udptable, NULL);
+
          if (!sk || udp_sk(sk)->encap_type) {
                  /* No socket for error: try tunnels before discarding */
-               sk = ERR_PTR(-ENOENT);
                  if (static_branch_unlikely(&udpv6_encap_needed_key)) {
                          sk = __udp6_lib_err_encap(net, hdr, offset, uh,
-                                                 udptable, skb,
+                                                 udptable, sk, skb,
                                                    opt, type, code, info);
                          if (!sk)
                                  return 0;
-               }
+               } else
+                       sk = ERR_PTR(-ENOENT);

                  if (IS_ERR(sk)) {
                          __ICMP6_INC_STATS(net, __in6_dev_get(skb->dev),
--

2.18.4