diff options
| author | Tom Gundersen <teg@jklm.no> | 2015-12-02 18:46:32 +0100 |
|---|---|---|
| committer | Tom Gundersen <teg@jklm.no> | 2015-12-10 17:04:42 +0100 |
| commit | 5d27351f8546530cf779847b0b04b0172c09f9d0 (patch) | |
| tree | 62e92deaf7a4a8c604d4c9905d3b2c1e87ba082e /src/resolve/resolved-dns-cache.c | |
| parent | 553947b77c3232d5795cbb2cd1129e74cb11c86d (diff) | |
resolved: cache - do negative caching only on the canonical name
Apart from dropping redundant information, this fixes an issue
where, due to broken DNS servers, we can only be certain of whether
an apparent NODATA response is in fact an NXDOMAIN response after
explicitly resolving the canonical name. This issue is outlined in
RFC2308. Moreover, by caching NXDOMAIN for an existing name, we
would mistakenly return NXDOMAIN for types which should not be
redirected. I.e., a query for AAAA on test-nx-1.jklm.no correctly
returns NXDOMAIN, but a query for CNAME should return the record
and a query for DNAME should return NODATA.
Note that this means we will not cache an NXDOMAIN response in the
presence of redirection, meaning one redundant roundtrip in case the
name is queried again.
Diffstat (limited to 'src/resolve/resolved-dns-cache.c')
| -rw-r--r-- | src/resolve/resolved-dns-cache.c | 9 |
1 files changed, 9 insertions, 0 deletions
diff --git a/src/resolve/resolved-dns-cache.c b/src/resolve/resolved-dns-cache.c index 4aacc268e2..008277ab09 100644 --- a/src/resolve/resolved-dns-cache.c +++ b/src/resolve/resolved-dns-cache.c @@ -479,6 +479,15 @@ int dns_cache_put( if (r > 0) return 0; + /* But not if it has a matching CNAME/DNAME (the negative + * caching will be done on the canonical name, not on the + * alias) */ + r = dns_answer_find_cname_or_dname(answer, key, NULL); + if (r < 0) + goto fail; + if (r > 0) + return 0; + /* See https://tools.ietf.org/html/rfc2308, which say that a * matching SOA record in the packet is used to to enable * negative caching. */ |