From 62efdf81734c6648986c2e8083dd2c99df544fcd Mon Sep 17 00:00:00 2001
From: Lennart Poettering <lennart@poettering.net>
Date: Mon, 7 Oct 2024 13:03:51 +0200
Subject: [PATCH] resolved: fix fastopen fallback

We should not invalidate the socket address size before we use it.

Fixes: #34579
(cherry picked from commit 5699e4c2d470a12c922c4b7c86a8987837911626)
(cherry picked from commit 964f7772ad0ff637db80ae0a9e0afb41a40f5b04)
(cherry picked from commit 4dca5688cb4c97f9072fe1c668923b2e56bfdf15)
(cherry picked from commit 969f4f3ea1163a5caa2b22ca05ea68aaed97034b)
---
 src/resolve/resolved-dns-stream.c | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/src/resolve/resolved-dns-stream.c b/src/resolve/resolved-dns-stream.c
index 50b069abee..6a5358a248 100644
--- a/src/resolve/resolved-dns-stream.c
+++ b/src/resolve/resolved-dns-stream.c
@@ -205,6 +205,7 @@ static int dns_stream_identify(DnsStream *s) {
 
 ssize_t dns_stream_writev(DnsStream *s, const struct iovec *iov, size_t iovcnt, int flags) {
         ssize_t m;
+        int r;
 
         assert(s);
         assert(iov);
@@ -224,12 +225,14 @@ ssize_t dns_stream_writev(DnsStream *s, const struct iovec *iov, size_t iovcnt,
 
                 m = sendmsg(s->fd, &hdr, MSG_FASTOPEN);
                 if (m < 0) {
-                        if (errno == EOPNOTSUPP) {
-                                s->tfo_salen = 0;
-                                if (connect(s->fd, &s->tfo_address.sa, s->tfo_salen) < 0)
-                                        return -errno;
+                        if (ERRNO_IS_NOT_SUPPORTED(errno)) {
+                                /* MSG_FASTOPEN not supported? Then try to connect() traditionally */
+                                r = RET_NERRNO(connect(s->fd, &s->tfo_address.sa, s->tfo_salen));
+                                s->tfo_salen = 0; /* connection is made */
+                                if (r < 0 && r != -EINPROGRESS)
+                                        return r;
 
-                                return -EAGAIN;
+                                return -EAGAIN; /* In case of EINPROGRESS, EAGAIN or success: return EAGAIN, so that caller calls us again */
                         }
                         if (errno == EINPROGRESS)
                                 return -EAGAIN;