From: Lennart Poettering <lennart@poettering.net>
Date: Mon, 3 Mar 2025 23:17:21 +0000 (+0100)
Subject: dns-stream: only read DNS packet data if we identified the peer properly
X-Git-Tag: v257.4~6
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=11da52785c978369e4cd92e67e5017a436404340;p=thirdparty%2Fsystemd.git

dns-stream: only read DNS packet data if we identified the peer properly

If we use TCP fastopen to connect to a DNS server via TCP, and it
responds really quickly between our connection attempt and our immediate
check back, then we have not identified the peer yet, and will not be
able to use the peer metadata to fill in our packet info.

Let's fix that, and simply not read from the socket until identification
is complete.

Fixes: #34956
(cherry picked from commit facc9439a76b4c3a5c273c71bd7a676e4c74778c)
---

diff --git a/src/resolve/resolved-dns-stream.c b/src/resolve/resolved-dns-stream.c
index e57af662218..eb9166105a2 100644
--- a/src/resolve/resolved-dns-stream.c
+++ b/src/resolve/resolved-dns-stream.c
@@ -360,7 +360,8 @@ static int on_stream_io(sd_event_source *es, int fd, uint32_t revents, void *use
                 }
         }
 
-        while ((revents & (EPOLLIN|EPOLLHUP|EPOLLRDHUP)) &&
+        while (s->identified && /* Only read data once we identified the peer, because we cannot fill in the DNS packet meta info otherwise */
+               (revents & (EPOLLIN|EPOLLHUP|EPOLLRDHUP)) &&
                (!s->read_packet ||
                 s->n_read < sizeof(s->read_size) + s->read_packet->size)) {