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resolved: Avoid multiple SSL writes per DoT packet

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In the DoT case, dns_stream_writev decomposed an iovec into multiple
dnstls_stream_write calls, which resulted in multiple SSL writes and multiple
TLS records. This can be checked from a network capture, e.g. using socat:
socat -v -x openssl-listen:853,reuseaddr,fork,cert=my.cert,key=my.key,verify=0 openssl:8.8.8.8:853

Instead, propagate the iovec as-is into the DoT handling code. For GnuTLS, the
library provides support for buffering ('corking') a record. OpenSSL has no
such facility, so we join the iovec into a single buffer then call SSL_write.

socat capture of `resolvectl -4 query --cache=no example.com` before the commit:

> 2022/01/30 13:35:52.194200  length=2 from=0 to=1
 00 28                                            .(
--
> 2022/01/30 13:35:52.194253  length=40 from=2 to=41
 1e b2 01 00 00 01 00 00 00 00 00 01 07 65 78 61  .............exa
 6d 70 6c 65 03 63 6f 6d 00 00 01 00 01 00 00 29  mple.com.......)
 ff e4 00 00 00 00 00 00                          ........
--
< 2022/01/30 13:35:52.232798  length=58 from=0 to=57
 00 38 1e b2 81 80 00 01 00 01 00 00 00 01 07 65  .8.............e
 78 61 6d 70 6c 65 03 63 6f 6d 00 00 01 00 01 c0  xample.com......
 0c 00 01 00 01 00 00 53 6f 00 04 5d b8 d8 22 00  .......So..]..".
 00 29 02 00 00 00 00 00 00 00                    .)........

socat capture of `resolvectl -4 query --cache=no example.com` after the commit:

> 2022/01/30 13:34:47.598099  length=42 from=504 to=545
 00 28 37 86 01 00 00 01 00 00 00 00 00 01 07 65  .(7............e
 78 61 6d 70 6c 65 03 63 6f 6d 00 00 01 00 01 00  xample.com......
 00 29 ff e4 00 00 00 00 00 00                    .)........
--
< 2022/01/30 13:34:47.613203  length=58 from=756 to=813
 00 38 37 86 81 80 00 01 00 01 00 00 00 01 07 65  .87............e
 78 61 6d 70 6c 65 03 63 6f 6d 00 00 01 00 01 c0  xample.com......
 0c 00 01 00 01 00 00 52 5e 00 04 5d b8 d8 22 00  .......R^..]..".
 00 29 02 00 00 00 00 00 00 00                    .)........

(cherry picked from commit aa892849d50e9dd5da03a628463ccf6c55ff1b44)
This commit is contained in:
Joan Bruguera 2022-01-31 21:28:32 +01:00 committed by Yu Watanabe
parent 3227f542a7
commit 03692af607
4 changed files with 46 additions and 27 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

18
src/resolve/resolved-dns-stream.c
View File

@ -210,22 +210,10 @@ ssize_t dns_stream_writev(DnsStream *s, const struct iovec *iov, size_t iovcnt,
assert(iov);
#if ENABLE_DNS_OVER_TLS
if (s->encrypted && !(flags & DNS_STREAM_WRITE_TLS_DATA)) {
ssize_t ss;
size_t i;
m = 0;
for (i = 0; i < iovcnt; i++) {
ss = dnstls_stream_write(s, iov[i].iov_base, iov[i].iov_len);
if (ss < 0)
return ss;
m += ss;
if (ss != (ssize_t) iov[i].iov_len)
continue;
}
} else
if (s->encrypted && !(flags & DNS_STREAM_WRITE_TLS_DATA))
return dnstls_stream_writev(s, iov, iovcnt);
#endif
if (s->tfo_salen > 0) {
struct msghdr hdr = {
.msg_iov = (struct iovec*) iov,

22
src/resolve/resolved-dnstls-gnutls.c
View File

@ -6,6 +6,7 @@
#include <gnutls/socket.h>
#include "io-util.h"
#include "resolved-dns-stream.h"
#include "resolved-dnstls.h"
#include "resolved-manager.h"
@ -13,7 +14,7 @@
#define TLS_PROTOCOL_PRIORITY "NORMAL:-VERS-ALL:+VERS-TLS1.3:+VERS-TLS1.2"
DEFINE_TRIVIAL_CLEANUP_FUNC_FULL(gnutls_session_t, gnutls_deinit, NULL);
static ssize_t dnstls_stream_writev(gnutls_transport_ptr_t p, const giovec_t *iov, int iovcnt) {
static ssize_t dnstls_stream_vec_push(gnutls_transport_ptr_t p, const giovec_t *iov, int iovcnt) {
int r;
assert(p);
@ -81,7 +82,7 @@ int dnstls_stream_connect_tls(DnsStream *stream, DnsServer *server) {
gnutls_handshake_set_timeout(gs, GNUTLS_DEFAULT_HANDSHAKE_TIMEOUT);
gnutls_transport_set_ptr2(gs, (gnutls_transport_ptr_t) (long) stream->fd, stream);
gnutls_transport_set_vec_push_function(gs, &dnstls_stream_writev);
gnutls_transport_set_vec_push_function(gs, &dnstls_stream_vec_push);
stream->encrypted = true;
stream->dnstls_data.handshake = gnutls_handshake(gs);
@ -163,15 +164,26 @@ int dnstls_stream_shutdown(DnsStream *stream, int error) {
return 0;
}
ssize_t dnstls_stream_write(DnsStream *stream, const char *buf, size_t count) {
ssize_t dnstls_stream_writev(DnsStream *stream, const struct iovec *iov, size_t iovcnt) {
ssize_t ss;
assert(stream);
assert(stream->encrypted);
assert(stream->dnstls_data.session);
assert(buf);
assert(iov);
assert(IOVEC_TOTAL_SIZE(iov, iovcnt) > 0);
ss = gnutls_record_send(stream->dnstls_data.session, buf, count);
gnutls_record_cork(stream->dnstls_data.session);
for (size_t i = 0; i < iovcnt; i++) {
ss = gnutls_record_send(
stream->dnstls_data.session,
iov[i].iov_base, iov[i].iov_len);
if (ss < 0)
break;
}
ss = gnutls_record_uncork(stream->dnstls_data.session, 0);
if (ss < 0)
switch(ss) {
case GNUTLS_E_INTERRUPTED:

30
src/resolve/resolved-dnstls-openssl.c
View File

@ -292,15 +292,10 @@ int dnstls_stream_shutdown(DnsStream *stream, int error) {
return 0;
}
ssize_t dnstls_stream_write(DnsStream *stream, const char *buf, size_t count) {
static ssize_t dnstls_stream_write(DnsStream *stream, const char *buf, size_t count) {
int error, r;
ssize_t ss;
assert(stream);
assert(stream->encrypted);
assert(stream->dnstls_data.ssl);
assert(buf);
ERR_clear_error();
ss = r = SSL_write(stream->dnstls_data.ssl, buf, count);
if (r <= 0) {
@ -329,6 +324,29 @@ ssize_t dnstls_stream_write(DnsStream *stream, const char *buf, size_t count) {
return ss;
}
ssize_t dnstls_stream_writev(DnsStream *stream, const struct iovec *iov, size_t iovcnt) {
_cleanup_free_ char *buf = NULL;
size_t count;
assert(stream);
assert(stream->encrypted);
assert(stream->dnstls_data.ssl);
assert(iov);
assert(IOVEC_TOTAL_SIZE(iov, iovcnt) > 0);
if (iovcnt == 1)
return dnstls_stream_write(stream, iov[0].iov_base, iov[0].iov_len);
/* As of now, OpenSSL can not accumulate multiple writes, so join into a
single buffer. Suboptimal, but better than multiple SSL_write calls. */
count = IOVEC_TOTAL_SIZE(iov, iovcnt);
buf = new(char, count);
for (size_t i = 0, pos = 0; i < iovcnt; pos += iov[i].iov_len, i++)
memcpy(buf + pos, iov[i].iov_base, iov[i].iov_len);
return dnstls_stream_write(stream, buf, count);
}
ssize_t dnstls_stream_read(DnsStream *stream, void *buf, size_t count) {
int error, r;
ssize_t ss;

3
src/resolve/resolved-dnstls.h
View File

@ -5,6 +5,7 @@
#include <stdbool.h>
#include <stdint.h>
#include <sys/uio.h>
typedef struct DnsServer DnsServer;
typedef struct DnsStream DnsStream;
@ -27,7 +28,7 @@ int dnstls_stream_connect_tls(DnsStream *stream, DnsServer *server);
void dnstls_stream_free(DnsStream *stream);
int dnstls_stream_on_io(DnsStream *stream, uint32_t revents);
int dnstls_stream_shutdown(DnsStream *stream, int error);
ssize_t dnstls_stream_write(DnsStream *stream, const char *buf, size_t count);
ssize_t dnstls_stream_writev(DnsStream *stream, const struct iovec *iov, size_t iovcnt);
ssize_t dnstls_stream_read(DnsStream *stream, void *buf, size_t count);
bool dnstls_stream_has_buffered_data(DnsStream *stream);