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resolved: Fall back to TCP if UDP is blocked

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If UDP is blocked on the system (e.g. by iptables or BPF), the kernel will
return EPERM on some or all of the system calls (connect, sendmsg, etc.).
In this case, try to fall back to TCP, which hopefully will not be blocked.

(cherry picked from commit 3dd6336ad0)
(cherry picked from commit a88e35bf95)
(cherry picked from commit 58cbb7a89b)
(cherry picked from commit 5f6a369a6a)
This commit is contained in:
Joan Bruguera 2023-02-12 20:06:08 +00:00 committed by Luca Boccassi
parent 85771e8df5
commit 74d5f34b0a
1 changed files with 3 additions and 1 deletions
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4
src/resolve/resolved-dns-transaction.c
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@ -2029,7 +2029,9 @@ int dns_transaction_go(DnsTransaction *t) {
log_debug("Sending query via TCP since it is too large.");
else if (r == -EAGAIN)
log_debug("Sending query via TCP since UDP isn't supported or DNS-over-TLS is selected.");
if (IN_SET(r, -EMSGSIZE, -EAGAIN))
else if (r == -EPERM)
log_debug("Sending query via TCP since UDP is blocked.");
if (IN_SET(r, -EMSGSIZE, -EAGAIN, -EPERM))
r = dns_transaction_emit_tcp(t);
}
if (r == -ELOOP) {