TrueCloudLab/coredns
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Change default value to 1232 (#6183)

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* Change default value to 1232

As specified by DNS flag day 2020, good and decent default value
avoiding fragmentation issues should be 1232. It is quite likely 1500
would work reliably on local ethernet networks.

Value 512 is set implicitly and must be used for all clients, which did
not include OPT RR with explicit value they support.

Since MR #5368 it should work correctly.

Signed-off-by: Petr Menšík <pemensik@redhat.com>

* Adapt bufsize test to new default value

Check also buffer size smaller than legacy value is not accepted.

Signed-off-by: Petr Menšík <pemensik@redhat.com>

* Update bufsize documentation

Mention also increasing request size is not possible, it can only reduce
the accepted size.

Signed-off-by: Petr Menšík <pemensik@redhat.com>

---------

Signed-off-by: Petr Menšík <pemensik@redhat.com>
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Petr Menšík 2023-07-10 16:49:52 +02:00 • committed by GitHub
parent 7569d132a1
commit 52f0348312
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3 changed files with 16 additions and 10 deletions
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16
plugin/bufsize/README.md
View file

@ -1,11 +1,15 @@
# bufsize
## Name
*bufsize* - sizes EDNS0 buffer size to prevent IP fragmentation.
*bufsize* - limits EDNS0 buffer size to prevent IP fragmentation.
## Description
*bufsize* limits a requester's UDP payload size.
*bufsize* limits a requester's UDP payload size to within a maximum value.
If a request with an OPT RR has a bufsize greater than the limit, the bufsize
of the request will be reduced. Otherwise the request is unaffected.
It prevents IP fragmentation, mitigating certain DNS vulnerabilities.
This will only affect queries that have an OPT RR.
It cannot increase UDP size requested by the client, it can be reduced only.
This will only affect queries that have
an OPT RR ([EDNS(0)](https://www.rfc-editor.org/rfc/rfc6891)).
## Syntax
```txt
@ -13,14 +17,14 @@ bufsize [SIZE]
```
**[SIZE]** is an int value for setting the buffer size.
The default value is 512, and the value must be within 512 - 4096.
The default value is 1232, and the value must be within 512 - 4096.
Only one argument is acceptable, and it covers both IPv4 and IPv6.
## Examples
Enable limiting the buffer size of outgoing query to the resolver (172.31.0.10):
```corefile
. {
bufsize 512
bufsize 1100
forward . 172.31.0.10
log
}
@ -29,7 +33,7 @@ Enable limiting the buffer size of outgoing query to the resolver (172.31.0.10):
Enable limiting the buffer size as an authoritative nameserver:
```corefile
. {
bufsize 512
bufsize 1220
file db.example.org
log
}

5
plugin/bufsize/setup.go
View file

@ -24,12 +24,13 @@ func setup(c *caddy.Controller) error {
}
func parse(c *caddy.Controller) (int, error) {
const defaultBufSize = 512
// value from http://www.dnsflagday.net/2020/
const defaultBufSize = 1232
for c.Next() {
args := c.RemainingArgs()
switch len(args) {
case 0:
// Nothing specified; use 512 as default
// Nothing specified; use defaultBufSize
return defaultBufSize, nil
case 1:
// Specified value is needed to verify

5
plugin/bufsize/setup_test.go
View file

@ -14,10 +14,11 @@ func TestSetupBufsize(t *testing.T) {
expectedData int
expectedErrContent string // substring from the expected error. Empty for positive cases.
}{
{`bufsize`, false, 512, ""},
{`bufsize "1232"`, false, 1232, ""},
{`bufsize`, false, 1232, ""},
{`bufsize "1220"`, false, 1220, ""},
{`bufsize "5000"`, true, -1, "plugin"},
{`bufsize "512 512"`, true, -1, "plugin"},
{`bufsize "511"`, true, -1, "plugin"},
{`bufsize "abc123"`, true, -1, "plugin"},
}