Public bug reported: [impact]
for DNS UDP replies larger than 512 bytes, fallback to TCP is used. For example 'host toomany.ddstreet.org'. Due to a bug in resolved in refcounting DNS stream types, the refcount underflows for type 0 streams (which resolved uses to talk to upstream nameservers), resulting in resolved being unable to fallback to TCP to handle truncated UDP replies. [test case] ubuntu@sf247344-upstream:~$ dig +noanswer +noedns toomany.ddstreet.org ;; Truncated, retrying in TCP mode. ; <<>> DiG 9.11.3-1ubuntu1.9-Ubuntu <<>> +noanswer +noedns toomany.ddstreet.org ;; global options: +cmd ;; Got answer: ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 2683 ;; flags: qr rd ra; QUERY: 1, ANSWER: 40, AUTHORITY: 0, ADDITIONAL: 0 ;; QUESTION SECTION: ;toomany.ddstreet.org. IN A ;; Query time: 0 msec ;; SERVER: 127.0.0.53#53(127.0.0.53) ;; WHEN: Thu Oct 24 11:40:29 UTC 2019 ;; MSG SIZE rcvd: 678 ubuntu@sf247344-upstream:~$ sudo resolvectl flush-caches ubuntu@sf247344-upstream:~$ dig +noanswer +noedns toomany.ddstreet.org ; <<>> DiG 9.11.3-1ubuntu1.9-Ubuntu <<>> +noanswer +noedns toomany.ddstreet.org ;; global options: +cmd ;; connection timed out; no servers could be reached [regression potential] very low, as this only properly sets the stream type in the DnsStream object; any regression would be a failure to be able to use TCP for DNS requests or replies. [other info] https://github.com/systemd/systemd/pull/13838 The commit adding stream types is not present in x/b, so this is needed only for disco and later. ** Affects: systemd (Ubuntu) Importance: Medium Assignee: Dan Streetman (ddstreet) Status: In Progress ** Affects: systemd (Ubuntu Disco) Importance: Medium Assignee: Dan Streetman (ddstreet) Status: In Progress ** Affects: systemd (Ubuntu Eoan) Importance: Medium Assignee: Dan Streetman (ddstreet) Status: In Progress ** Affects: systemd (Ubuntu Focal) Importance: Medium Assignee: Dan Streetman (ddstreet) Status: In Progress ** Tags: ddstreet disco eoan focal sts systemd ** Also affects: systemd (Ubuntu Focal) Importance: Undecided Status: New ** Also affects: systemd (Ubuntu Eoan) Importance: Undecided Status: New ** Description changed: [impact] for DNS UDP replies larger than 512 bytes, fallback to TCP is used. For example 'host toomany.ddstreet.org'. Due to a bug in resolved in refcounting DNS stream types, the refcount underflows for type 0 streams (which resolved uses to talk to upstream nameservers), resulting in resolved being unable to fallback to TCP to handle truncated UDP replies. [test case] ubuntu@sf247344-upstream:~$ dig +noanswer +noedns toomany.ddstreet.org ;; Truncated, retrying in TCP mode. ; <<>> DiG 9.11.3-1ubuntu1.9-Ubuntu <<>> +noanswer +noedns toomany.ddstreet.org ;; global options: +cmd ;; Got answer: ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 2683 ;; flags: qr rd ra; QUERY: 1, ANSWER: 40, AUTHORITY: 0, ADDITIONAL: 0 ;; QUESTION SECTION: ;toomany.ddstreet.org. IN A ;; Query time: 0 msec ;; SERVER: 127.0.0.53#53(127.0.0.53) ;; WHEN: Thu Oct 24 11:40:29 UTC 2019 ;; MSG SIZE rcvd: 678 - ubuntu@sf247344-upstream:~$ sudo resolvectl flush-caches + ubuntu@sf247344-upstream:~$ sudo resolvectl flush-caches ubuntu@sf247344-upstream:~$ dig +noanswer +noedns toomany.ddstreet.org ; <<>> DiG 9.11.3-1ubuntu1.9-Ubuntu <<>> +noanswer +noedns toomany.ddstreet.org ;; global options: +cmd ;; connection timed out; no servers could be reached [regression potential] very low, as this only properly sets the stream type in the DnsStream object; any regression would be a failure to be able to use TCP for DNS requests or replies. [other info] https://github.com/systemd/systemd/pull/13838 + + The commit adding stream types is not present in x/b, so this is needed + only for disco and later. ** Also affects: systemd (Ubuntu Disco) Importance: Undecided Status: New ** Changed in: systemd (Ubuntu Disco) Importance: Undecided => Medium ** Changed in: systemd (Ubuntu Eoan) Importance: Undecided => Medium ** Changed in: systemd (Ubuntu Focal) Importance: Undecided => Medium ** Changed in: systemd (Ubuntu Disco) Assignee: (unassigned) => Dan Streetman (ddstreet) ** Changed in: systemd (Ubuntu Eoan) Assignee: (unassigned) => Dan Streetman (ddstreet) ** Changed in: systemd (Ubuntu Eoan) Status: New => In Progress ** Changed in: systemd (Ubuntu Disco) Status: New => In Progress ** Changed in: systemd (Ubuntu Focal) Assignee: (unassigned) => Dan Streetman (ddstreet) ** Changed in: systemd (Ubuntu Focal) Status: New => In Progress ** Tags added: ddstreet disco eoan focal sts systemd -- You received this bug notification because you are a member of Ubuntu Touch seeded packages, which is subscribed to systemd in Ubuntu. https://bugs.launchpad.net/bugs/1849658 Title: resolved fallback to TCP fails for truncated UDP replies Status in systemd package in Ubuntu: In Progress Status in systemd source package in Disco: In Progress Status in systemd source package in Eoan: In Progress Status in systemd source package in Focal: In Progress Bug description: [impact] for DNS UDP replies larger than 512 bytes, fallback to TCP is used. For example 'host toomany.ddstreet.org'. Due to a bug in resolved in refcounting DNS stream types, the refcount underflows for type 0 streams (which resolved uses to talk to upstream nameservers), resulting in resolved being unable to fallback to TCP to handle truncated UDP replies. [test case] ubuntu@sf247344-upstream:~$ dig +noanswer +noedns toomany.ddstreet.org ;; Truncated, retrying in TCP mode. ; <<>> DiG 9.11.3-1ubuntu1.9-Ubuntu <<>> +noanswer +noedns toomany.ddstreet.org ;; global options: +cmd ;; Got answer: ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 2683 ;; flags: qr rd ra; QUERY: 1, ANSWER: 40, AUTHORITY: 0, ADDITIONAL: 0 ;; QUESTION SECTION: ;toomany.ddstreet.org. IN A ;; Query time: 0 msec ;; SERVER: 127.0.0.53#53(127.0.0.53) ;; WHEN: Thu Oct 24 11:40:29 UTC 2019 ;; MSG SIZE rcvd: 678 ubuntu@sf247344-upstream:~$ sudo resolvectl flush-caches ubuntu@sf247344-upstream:~$ dig +noanswer +noedns toomany.ddstreet.org ; <<>> DiG 9.11.3-1ubuntu1.9-Ubuntu <<>> +noanswer +noedns toomany.ddstreet.org ;; global options: +cmd ;; connection timed out; no servers could be reached [regression potential] very low, as this only properly sets the stream type in the DnsStream object; any regression would be a failure to be able to use TCP for DNS requests or replies. [other info] https://github.com/systemd/systemd/pull/13838 The commit adding stream types is not present in x/b, so this is needed only for disco and later. 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