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tls: Add options for verifying the peer certificate 

A file containing the trusted CA certificates needs to be
supplied via the ca_file AVOption, unless the TLS library
has got a system default file/database set up.

This doesn't check the hostname of the peer certificate with
openssl, which requires a non-trivial piece of code for
manually matching the desired hostname to the string provided
by the certificate, not provided as a library function.

That is, with openssl, this only validates that the received
certificate is signed with the right CA, but not that it is
the actual server we think we're talking to.

Verification is still disabled by default since we can't count
on a proper CA database existing at all times.

Signed-off-by: Martin Storsjö <martin@martin.st>
This commit is contained in:
Martin Storsjö 2011-02-22 12:02:01 +02:00
parent 4370f65be8
commit 8b09d917e7
3 changed files with 101 additions and 2 deletions
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33
doc/protocols.texi
View File

@ -568,6 +568,39 @@ avplay tcp://@var{hostname}:@var{port}
@end table
@section tls
Transport Layer Security (TLS) / Secure Sockets Layer (SSL)
The required syntax for a TLS url is:
@example
tls://@var{hostname}:@var{port}
@end example
The following parameters can be set via command line options
(or in code via @code{AVOption}s):
@table @option
@item ca_file
A file containing certificate authority (CA) root certificates to treat
as trusted. If the linked TLS library contains a default this might not
need to be specified for verification to work, but not all libraries and
setups have defaults built in.
@item tls_verify=@var{1|0}
If enabled, try to verify the peer that we are communicating with.
Note, if using OpenSSL, this currently only makes sure that the
peer certificate is signed by one of the root certificates in the CA
database, but it does not validate that the certificate actually
matches the host name we are trying to connect to. (With GnuTLS,
the host name is validated as well.)
This is disabled by default since it requires a CA database to be
provided by the caller in many cases.
@end table
@section udp
User Datagram Protocol.

68
libavformat/tls.c
View File

@ -22,8 +22,10 @@
#include "avformat.h"
#include "url.h"
#include "libavutil/avstring.h"
#include "libavutil/opt.h"
#if CONFIG_GNUTLS
#include <gnutls/gnutls.h>
#include <gnutls/x509.h>
#define TLS_read(c, buf, size) gnutls_record_recv(c->session, buf, size)
#define TLS_write(c, buf, size) gnutls_record_send(c->session, buf, size)
#define TLS_shutdown(c) gnutls_bye(c->session, GNUTLS_SHUT_RDWR)
@ -65,8 +67,26 @@ typedef struct {
SSL *ssl;
#endif
int fd;
char *ca_file;
int verify;
} TLSContext;
#define OFFSET(x) offsetof(TLSContext, x)
#define D AV_OPT_FLAG_DECODING_PARAM
#define E AV_OPT_FLAG_ENCODING_PARAM
static const AVOption options[] = {
{"ca_file", "Certificate Authority database file", OFFSET(ca_file), AV_OPT_TYPE_STRING, .flags = D|E },
{"tls_verify", "Verify the peer certificate", OFFSET(verify), AV_OPT_TYPE_INT, { .i64 = 0 }, 0, 1, .flags = D|E },
{ NULL }
};
static const AVClass tls_class = {
.class_name = "tls",
.item_name = av_default_item_name,
.option = options,
.version = LIBAVUTIL_VERSION_INT,
};
static int do_tls_poll(URLContext *h, int ret)
{
TLSContext *c = h->priv_data;
@ -158,7 +178,14 @@ static int tls_open(URLContext *h, const char *uri, int flags)
if (!numerichost)
gnutls_server_name_set(c->session, GNUTLS_NAME_DNS, host, strlen(host));
gnutls_certificate_allocate_credentials(&c->cred);
gnutls_certificate_set_verify_flags(c->cred, 0);
if (c->ca_file)
gnutls_certificate_set_x509_trust_file(c->cred, c->ca_file, GNUTLS_X509_FMT_PEM);
#if GNUTLS_VERSION_MAJOR >= 3
else
gnutls_certificate_set_x509_system_trust(c->cred);
#endif
gnutls_certificate_set_verify_flags(c->cred, c->verify ?
GNUTLS_VERIFY_ALLOW_X509_V1_CA_CRT : 0);
gnutls_credentials_set(c->session, GNUTLS_CRD_CERTIFICATE, c->cred);
gnutls_transport_set_ptr(c->session, (gnutls_transport_ptr_t)
(intptr_t) c->fd);
@ -170,6 +197,38 @@ static int tls_open(URLContext *h, const char *uri, int flags)
if ((ret = do_tls_poll(h, ret)) < 0)
goto fail;
}
if (c->verify) {
unsigned int status, cert_list_size;
gnutls_x509_crt_t cert;
const gnutls_datum_t *cert_list;
if ((ret = gnutls_certificate_verify_peers2(c->session, &status)) < 0) {
av_log(h, AV_LOG_ERROR, "Unable to verify peer certificate: %s\n",
gnutls_strerror(ret));
ret = AVERROR(EIO);
goto fail;
}
if (status & GNUTLS_CERT_INVALID) {
av_log(h, AV_LOG_ERROR, "Peer certificate failed verification\n");
ret = AVERROR(EIO);
goto fail;
}
if (gnutls_certificate_type_get(c->session) != GNUTLS_CRT_X509) {
av_log(h, AV_LOG_ERROR, "Unsupported certificate type\n");
ret = AVERROR(EIO);
goto fail;
}
gnutls_x509_crt_init(&cert);
cert_list = gnutls_certificate_get_peers(c->session, &cert_list_size);
gnutls_x509_crt_import(cert, cert_list, GNUTLS_X509_FMT_DER);
ret = gnutls_x509_crt_check_hostname(cert, host);
gnutls_x509_crt_deinit(cert);
if (!ret) {
av_log(h, AV_LOG_ERROR,
"The certificate's owner does not match hostname %s\n", host);
ret = AVERROR(EIO);
goto fail;
}
}
#elif CONFIG_OPENSSL
c->ctx = SSL_CTX_new(TLSv1_client_method());
if (!c->ctx) {
@ -177,6 +236,12 @@ static int tls_open(URLContext *h, const char *uri, int flags)
ret = AVERROR(EIO);
goto fail;
}
if (c->ca_file)
SSL_CTX_load_verify_locations(c->ctx, c->ca_file, NULL);
// Note, this doesn't check that the peer certificate actually matches
// the requested hostname.
if (c->verify)
SSL_CTX_set_verify(c->ctx, SSL_VERIFY_PEER, NULL);
c->ssl = SSL_new(c->ctx);
if (!c->ssl) {
av_log(h, AV_LOG_ERROR, "%s\n", ERR_error_string(ERR_get_error(), NULL));
@ -256,4 +321,5 @@ URLProtocol ff_tls_protocol = {
.url_close = tls_close,
.priv_data_size = sizeof(TLSContext),
.flags = URL_PROTOCOL_FLAG_NETWORK,
.priv_data_class = &tls_class,
};

2
libavformat/version.h
View File

@ -31,7 +31,7 @@
#define LIBAVFORMAT_VERSION_MAJOR 55
#define LIBAVFORMAT_VERSION_MINOR 5
#define LIBAVFORMAT_VERSION_MICRO 1
#define LIBAVFORMAT_VERSION_MICRO 2
#define LIBAVFORMAT_VERSION_INT AV_VERSION_INT(LIBAVFORMAT_VERSION_MAJOR, \
LIBAVFORMAT_VERSION_MINOR, \