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net: bring domain name length checks into RFC compliance

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The 255-octet limit applies to wire format, not presentation format.

Fixes #17549

Change-Id: I2b5181c53fba32fea60178e0d8df9114aa992b55
Reviewed-on: https://go-review.googlesource.com/31722
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>
This commit is contained in:
Richard Gibson 2016-10-22 00:21:18 -04:00 • committed by Russ Cox
parent add721ef91
commit 9a5bddd7ed
4 changed files with 90 additions and 21 deletions
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15
src/net/dnsclient_unix.go
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@ -362,14 +362,21 @@ func (conf *dnsConfig) nameList(name string) []string {
return nil
}
// Check name length (see isDomainName).
l := len(name)
rooted := l > 0 && name[l-1] == '.'
if l > 254 || l == 254 && rooted {
return nil
}
// If name is rooted (trailing dot), try only that name.
rooted := len(name) > 0 && name[len(name)-1] == '.'
if rooted {
return []string{name}
}
hasNdots := count(name, '.') >= conf.ndots
name += "."
l++
// Build list of search choices.
names := make([]string, 0, 1+len(conf.search))
@ -377,9 +384,11 @@ func (conf *dnsConfig) nameList(name string) []string {
if hasNdots {
names = append(names, name)
}
// Try suffixes.
// Try suffixes that are not too long (see isDomainName).
for _, suffix := range conf.search {
names = append(names, name+suffix)
if l+len(suffix) <= 254 {
names = append(names, name+suffix)
}
}
// Try unsuffixed, if not tried first above.
if !hasNdots {