On Fri, Jul 31, 2020 at 09:12:10AM -0700, Eric Dumazet wrote:

On Thu, Jul 30, 2020 at 1:58 PM Martin KaFai Lau [off-list ref] wrote:

quoted

In the latter patch, the bpf prog only wants to be called to handle
a header option if that particular header option cannot be handled by
the kernel.  This unknown option could be written by the peer's bpf-prog.
It could also be a new standard option that the running kernel does not
support it while a bpf-prog can handle it.

In a latter patch, the bpf prog will be called from tcp_validate_incoming()
if there is unknown option and a flag is set in tp->bpf_sock_ops_cb_flags.

Instead of using skb->cb[] in an earlier attempt, this patch
adds an optional arg "bool *unknown_opt" to tcp_parse_options().
The bool will be set to true if it has encountered an option
that the kernel does not recognize.

Signed-off-by: Martin KaFai Lau <redacted>
---
 drivers/infiniband/hw/cxgb4/cm.c |  2 +-
 include/net/tcp.h                |  3 ++-
 net/ipv4/syncookies.c            |  2 +-
 net/ipv4/tcp_input.c             | 40 +++++++++++++++++++++-----------
 net/ipv4/tcp_minisocks.c         |  4 ++--
 net/ipv6/syncookies.c            |  2 +-
 6 files changed, 34 insertions(+), 19 deletions(-)

diff --git a/drivers/infiniband/hw/cxgb4/cm.c b/drivers/infiniband/hw/cxgb4/cm.c
index 30e08bcc9afb..dedca6576bb9 100644
--- a/drivers/infiniband/hw/cxgb4/cm.c
+++ b/drivers/infiniband/hw/cxgb4/cm.c

@@ -3949,7 +3949,7 @@ static void build_cpl_pass_accept_req(struct sk_buff *skb, int stid , u8 tos)
         */
        memset(&tmp_opt, 0, sizeof(tmp_opt));
        tcp_clear_options(&tmp_opt);
-       tcp_parse_options(&init_net, skb, &tmp_opt, 0, NULL);
+       tcp_parse_options(&init_net, skb, &tmp_opt, 0, NULL, NULL);

        req = __skb_push(skb, sizeof(*req));
        memset(req, 0, sizeof(*req));

diff --git a/include/net/tcp.h b/include/net/tcp.h
index 895e7aabf136..d49d8f1c961a 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h

@@ -413,7 +413,8 @@ int tcp_mmap(struct file *file, struct socket *sock,
 #endif
 void tcp_parse_options(const struct net *net, const struct sk_buff *skb,
                       struct tcp_options_received *opt_rx,
-                      int estab, struct tcp_fastopen_cookie *foc);
+                      int estab, struct tcp_fastopen_cookie *foc,
+                      bool *unknown_opt);
 const u8 *tcp_parse_md5sig_option(const struct tcphdr *th);

Instead of changing signatures of many functions (and make future
stable backports challenging)
how about adding a field into 'struct tcp_options_received' ?

Sounds good.  There is a one byte hole in 'struct tcp_options_received',
so it won't matter much even there is "rx_opt" in "struct tcp_sock".