samples/mbedtls_sslclient: Discards TLS records, handshake does not work

[vakulgarg]

I encountered a scenario where TLS handshake got broken. The mbedtls stack discarded tls records assuming corrupt data.

Digging further, I found that the way the incoming TLS records have been fed to mbedtls stack is wrong. Specifically, in function tcp_rx() (inside mbedtls_sslclient/src/tcp.c), the function always copies 'read_bytes' of data in input buffer 'buf' even if the requested input len given in 'size' parameter is less than 'read_bytes'. This could cause buffer overflow. Further, mbedtls stack disards whatever extra (i.e. read_bytes - size) that has been copied in tcp_rx() in 'buf'.

Perhaps, it would have been simpler and user-friendly, if instead of net_context apis, POSIX style sockets had been used in this example.

[Mras2an]

Hi,
I have the same issue!

[pfalcon]

Note that there're examples how to use mbedTLS with POSIX sockets: #5985 .

[Mras2an]

Tkx pfalcon, May you tell me were I can find your example code?
I would like open a socket with mbedtls on the NXP FRDM-K64F board. I have tested the mbedtls_sslclient but it didn't work. Is it possible to use POSIX sockets into this example?

[jukkar]

Perhaps, it would have been simpler and user-friendly, if instead of net_context apis, POSIX style sockets had been used in this example.

When this sample application was created, there was no bsd socket support in zephyr. You are welcome to send patches that convert this app to use bsd sockets.

[jukkar]

The application has bitrotted, I will send fixed prj.conf file shortly.

I followed the steps described in the README file but used qemu instead of real device.

Starting the server in host side:

./programs/ssl/ssl_server2 psk=000102030405060708090a0b0c0d0e0f server_addr=192.0.2.2

  . Seeding the random number generator... ok
  . Bind on tcp://192.0.2.2:4433/ ... ok
  . Setting up the SSL/TLS structure... ok
  . Waiting for a remote connection ... ok
  . Performing the SSL/TLS handshake... ok
    [ Protocol is TLSv1.2 ]
    [ Ciphersuite is TLS-PSK-WITH-AES-256-CCM-8 ]
    [ Record expansion is 21 ]
  < Read from client: 18 bytes read

GET / HTTP/1.0


  > Write to client: 139 bytes written in 1 fragments

HTTP/1.0 200 OK
Content-Type: text/html

<h2>mbed TLS Test Server</h2>
<p>Successful connection using: TLS-PSK-WITH-AES-256-CCM-8</p>

  . Closing the connection... done
  . Waiting for a remote connection ...^C interrupted by signal
  . Cleaning up... done.

And the zephyr side:

***** Booting Zephyr OS v1.11.0-1168-g03f9f66496 *****
Zephyr Shell, Zephyr version: 1.11.99
Type 'help' for a list of available commands
shell> 
  . Seeding the random number generator... ok
  . Setting up the SSL/TLS structure... ok
  . Connecting to tcp 192.0.2.2... ok
  . Performing the SSL/TLS handshake... ok
  > Write to server: ok
  . Closing the connection... done
QEMU: Terminated
[100%] Built target run

[Mras2an]

tkx jukkar, I will test with QEMU.

[xianrenqiu]

I did a test in the qemu_x86, only a few times can run successfully, but most of them fail. @Mras2an has it been successful in the QEMU environment？

In addition, I also tried to use the configuration file provided by mbedtls(config-suite-b.h), The server certificate will be verified，but the handshake was not successful. @jukkar is there have a similar sample program? thanks