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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)
This commit is contained in:
Joan Bruguera 2023-02-12 20:06:08 +00:00 committed by Zbigniew Jędrzejewski-Szmek
parent e91a304274
commit 58cbb7a89b
1 changed files with 3 additions and 1 deletions
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4
src/resolve/resolved-dns-transaction.c
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@ -2079,7 +2079,9 @@ 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) {