** Changed in: systemd (Ubuntu)
Status: New => Fix Released
** Tags added: bionic ddstreet disco eoan systemd
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https://bugs.launchpad.net/bugs/1849733
Title:
resolved incorrectly limits TCP reply to edns0 payload
Status in systemd package in Ubuntu:
Fix Released
Status in systemd source package in Bionic:
In Progress
Status in systemd source package in Disco:
In Progress
Status in systemd source package in Eoan:
Fix Released
Bug description:
[impact]
glibc's getaddrinfo() uses EDNS0 to talk to resolved, and it sets its
payload limit to 1200. When the response is larger than 1200,
resolved will limit the response and set the truncate flag. This
causes getaddrinfo() to switch to TCP and request again, but glibc
incorrectly keeps the EDNS0 RR opt, with the same 1200 payload limit.
Most dns nameservers ignore EDNS0 payload limit for TCP, since per RFC
it applies only to UDP, but resolved does not and again marks the
response as truncated. This prevents getaddrinfo() from being able to
resolve any records with a response over 1200 bytes.
[test case]
use ping or telnet, which use getaddrinfo(), to lookup an A record
with a lot of results, like toomany100.ddstreet.org
$ telnet toomany100.ddstreet.org
telnet: could not resolve toomany100.ddstreet.org/telnet: Temporary failure
in name resolution
[regression potential]
any regression would likely result in failure to correctly lookup a
hostname or to provide the correct response to a local client.
[other info]
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