[FFmpeg-devel] [PATCH 6/6] lavf/tls_mbedtls: add workaround for TLSv1.3 vs. verify=0

[FFmpeg-devel] [PATCH 6/6] lavf/tls_mbedtls: add workaround for TLSv1.3 vs. verify=0

[Sfan5]

As of mbedTLS 3.6.0 TLSv1.3 is enabled by default and certificate 
verification
is now mandatory. Our default configuration does not do verification, so
downgrade to 1.2 in these situations to avoid breaking it.

ref: https://github.com/Mbed-TLS/mbedtls/issues/7075
Signed-off-by: sfan5 <sfan5@live.de>
---
  libavformat/tls_mbedtls.c | 12 ++++++++++++
  1 file changed, 12 insertions(+)

diff --git a/libavformat/tls_mbedtls.c b/libavformat/tls_mbedtls.c
index 8268e74638..5d5c7bfb25 100644
--- a/libavformat/tls_mbedtls.c
+++ b/libavformat/tls_mbedtls.c
@@ -163,6 +163,10 @@ static void handle_handshake_error(URLContext *h, 
int ret)
      case MBEDTLS_ERR_SSL_INTERNAL_ERROR:
          av_log(h, AV_LOG_ERROR, "Internal error encountered.\n");
          break;
+    case MBEDTLS_ERR_X509_CERT_VERIFY_FAILED:
+        // This error only happens with TLSv1.3, we normally use 
mbedtls_ssl_get_verify_result().
+        av_log(h, AV_LOG_ERROR, "Certificate verification failed.\n");
+        break;
      case MBEDTLS_ERR_NET_CONN_RESET:
          av_log(h, AV_LOG_ERROR, "TLS handshake was aborted by peer.\n");
          break;
@@ -263,6 +267,14 @@ static int tls_open(URLContext *h, const char *uri, 
int flags, AVDictionary **op
          goto fail;
      }
  +#ifdef MBEDTLS_SSL_PROTO_TLS1_3
+    // mbedTLS does not allow disabling certificate verification with 
TLSv1.3 (yes, really).
+    if (!shr->verify) {
+        av_log(h, AV_LOG_INFO, "Forcing TLSv1.2 because certificate 
verification is disabled\n");
+        mbedtls_ssl_conf_max_tls_version(&tls_ctx->ssl_config, 
MBEDTLS_SSL_VERSION_TLS1_2);
+    }
+#endif
+
      // not VERIFY_REQUIRED because we manually check after handshake
      mbedtls_ssl_conf_authmode(&tls_ctx->ssl_config,
                                shr->verify ? 
MBEDTLS_SSL_VERIFY_OPTIONAL : MBEDTLS_SSL_VERIFY_NONE);
-- 
2.45.1

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Re: [FFmpeg-devel] [PATCH 6/6] lavf/tls_mbedtls: add workaround for TLSv1.3 vs. verify=0

[Anton Khirnov]

Quoting Sfan5 (2024-05-17 10:34:50)
> As of mbedTLS 3.6.0 TLSv1.3 is enabled by default and certificate 
> verification
> is now mandatory. Our default configuration does not do verification, so
> downgrade to 1.2 in these situations to avoid breaking it.
> 
> ref: https://github.com/Mbed-TLS/mbedtls/issues/7075
> Signed-off-by: sfan5 <sfan5@live.de>
> ---

Would it not be simpler to simply set authmode to
MBEDTLS_SSL_VERIFY_OPTIONAL unconditionally, then just disregard the
verification result?

-- 
Anton Khirnov
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Re: [FFmpeg-devel] [PATCH 6/6] lavf/tls_mbedtls: add workaround for TLSv1.3 vs. verify=0

[sfan5]

Am 11.06.24 um 17:02 schrieb Anton Khirnov:
> Quoting Sfan5 (2024-05-17 10:34:50)
>> As of mbedTLS 3.6.0 TLSv1.3 is enabled by default and certificate
>> verification
>> is now mandatory. Our default configuration does not do verification, so
>> downgrade to 1.2 in these situations to avoid breaking it.
>>
>> ref: https://github.com/Mbed-TLS/mbedtls/issues/7075
>> Signed-off-by: sfan5 <sfan5@live.de>
>> ---
> Would it not be simpler to simply set authmode to
> MBEDTLS_SSL_VERIFY_OPTIONAL unconditionally, then just disregard the
> verification result?
>
That's the thing and it's exactly as stupid as it sounds: When using 
TLSv1.3 it will ignore the MBEDTLS_SSL_VERIFY mode entirely.

If the verification doesn't pass the handshake fails and you don't get 
an usable connection. I'm hoping the mbedTLS devs realize at some point 
how nonviable this is and fix it but as of right now this is the only 
way to not have ffmpeg "randomly" (depending on if the server speaks 
TLSv1.3) fail with mbedTLS 3.6.0.

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Re: [FFmpeg-devel] [PATCH 6/6] lavf/tls_mbedtls: add workaround for TLSv1.3 vs. verify=0

[Anton Khirnov]

Quoting sfan5 (2024-06-11 18:17:00)
> Am 11.06.24 um 17:02 schrieb Anton Khirnov:
> > Quoting Sfan5 (2024-05-17 10:34:50)
> >> As of mbedTLS 3.6.0 TLSv1.3 is enabled by default and certificate
> >> verification
> >> is now mandatory. Our default configuration does not do verification, so
> >> downgrade to 1.2 in these situations to avoid breaking it.
> >>
> >> ref: https://github.com/Mbed-TLS/mbedtls/issues/7075
> >> Signed-off-by: sfan5 <sfan5@live.de>
> >> ---
> > Would it not be simpler to simply set authmode to
> > MBEDTLS_SSL_VERIFY_OPTIONAL unconditionally, then just disregard the
> > verification result?
> >
> That's the thing and it's exactly as stupid as it sounds: When using 
> TLSv1.3 it will ignore the MBEDTLS_SSL_VERIFY mode entirely.
> 
> If the verification doesn't pass the handshake fails and you don't get 
> an usable connection. I'm hoping the mbedTLS devs realize at some point 
> how nonviable this is and fix it but as of right now this is the only 
> way to not have ffmpeg "randomly" (depending on if the server speaks 
> TLSv1.3) fail with mbedTLS 3.6.0.

uh...that sure is...special

Patch pushed then.

-- 
Anton Khirnov
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