LibreSSL does not tolerate setting minimum_version greater than maximum_version #78182

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1. alanhuang122 commented on Jun 29, 2018

   

   alanhuang122mannequin

   on Jun 29, 2018

   MannequinAuthor

   More actions

   LibreSSL has a function called ssl_clamp_version_range that is called before attempting to set the minimum and maximum protocol versions in ssl_version_set_{min,max}. The function disallows setting ranges that are invalid (i.e., where minimum_version > maximum_version). OpenSSL does not disallow this behavior.

   As a result, attempting to set a minimum_version greater than a maximum_version results in a ValueError when Python is built with LibreSSL.

   There are two things that might need fixing here:

   1. Replace the ValueError "Unsupported protocol version 0x%x" message with a more generic one. The assumption that the only way the operation can fail is if the underlying library does not support the protocol version is incorrect.
      This can be done by either making the message more generic or by introducing another error message to handle this case.
   2. Change test_min_max_version lines 3575-3576 to set the maximum_version before the minimum_version.

   Here's some Python code to reproduce the above-mentioned error:

   import ssl
   
   ctx = ssl.SSLContext()
   ctx.maximum_version = ssl.TLSVersion.TLSv1_1
   ctx.minimum_version = ssl.TLSVersion.TLSv1_2
   
   Traceback (most recent call last):
     File "<stdin>", line 1, in <module>
     File "/home/alan/src/cpython/Lib/ssl.py", line 491, in minimum_version
       super(SSLContext, SSLContext).minimum_version.__set__(self, value)
   ValueError: Unsupported protocol version 0x303
   

   Here's some example C code:

   #include <openssl/ssl.h>
   #include <openssl/ossl_typ.h>
   #include <stdio.h>
   
   int main(){
       SSL_CTX *ctx = NULL;
       ctx = SSL_CTX_new(TLS_method());
   
       printf("setting max to TLSv1.1: ");
       if(SSL_CTX_set_max_proto_version(ctx, TLS1_1_VERSION)){
           printf("success\n");
       }   
       else{
           printf("failure\n");
       }   
       printf("setting min to TLSv1.2: ");
       if(SSL_CTX_set_min_proto_version(ctx, TLS1_2_VERSION)){
           printf("success\n");
       }   
       else{
           printf("failure\n");
       }   
   
       printf("min ver: %d\n", SSL_CTX_get_min_proto_version(ctx));
       printf("max ver: %d\n", SSL_CTX_get_max_proto_version(ctx));
       return 0;
   }
   

   Under LibreSSL 2.7.4, this produces:

   setting max to TLSv1.1: success
   setting min to TLSv1.2: failure
   min ver: 769
   max ver: 770
   

   Under OpenSSL 1.1.0g, this produces:

   setting max to TLSv1.1: success
   setting min to TLSv1.2: success
   min ver: 771
   max ver: 770
   

   The test that failed:
   ======================================================================
   ERROR: test_min_max_version (test.test_ssl.ThreadedTests)
   ----------------------------------------------------------------------

   Traceback (most recent call last):
     File "/home/alan/src/cpython/Lib/test/test_ssl.py", line 3575, in test_min_max_version
       server_context.minimum_version = ssl.TLSVersion.TLSv1_2
     File "/home/alan/src/cpython/Lib/ssl.py", line 491, in minimum_version
       super(SSLContext, SSLContext).minimum_version.__set__(self, value)
   ValueError: Unsupported protocol version 0x303
2. alanhuang122

   added

   3.7 (EOL)end of lifeend of life

   3.8 (EOL)end of lifeend of life

   on Jun 29, 2018
3. alanhuang122

   assigned

   tiran

   on Jun 29, 2018
4. alanhuang122

   added

   testsTests in the Lib/test dirTests in the Lib/test dir

   topic-SSL

   type-bugAn unexpected behavior, bug, or errorAn unexpected behavior, bug, or error

   on Jun 29, 2018
5. alanhuang122 commented on Jul 2, 2018

   

   alanhuang122mannequin

   on Jul 2, 2018

   MannequinAuthor

   More actions

   Strangely, LibreSSL's ssl_clamp_version_range function is perfectly happy to accept minimum protocol versions lower than the lowest supported protocol version, and likewise is happy to accept maximum protocol versions higher than the highest supported protocol version.
   In said case, the minimum/maximum protocol version is set to clamp_min/clamp_max (i.e., the minimum/maximum protocol version supported by the internal method).

   As such, the assertion test ctx.minimum_version = 42 on line 1127 in test_min_max_version in test_ssl.py fails.

   A possible fix would be to add another check in set_min_max_proto_version _ssl.c that checks if the current set protocol version is equal to the value passed (with exceptions for the magic constants of MINIMUM_SUPPORTED and MAXIMUM_SUPPORTED), and if not, raise a ValueError as well.

   One dilemma is whether to reset the respective version back to what it was before the attempt, which I think should be done.
6. Yhg1s commented on Sep 11, 2019

   

   Yhg1s

   on Sep 11, 2019

   Member

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   New changeset c9bc49c by T. Wouters (Christian Heimes) in branch 'master':
   bpo-34001: Fix test_ssl with LibreSSL (GH-13783)
   c9bc49c
7. matrixise commented on Sep 11, 2019

   

   matrixise

   on Sep 11, 2019

   Member

   More actions

   New changeset d6ac67f by Stéphane Wirtel (Miss Islington (bot)) in branch '3.8':
   bpo-34001: Fix test_ssl with LibreSSL (GH-13783) (bpo-15997)
   d6ac67f
8. tiran

   closed this as completedon Apr 17, 2021
9. ezio-melotti

   transferred this issue fromon Apr 10, 2022
10. CyberTailor

    added 2 commits that reference this issue on Nov 2, 2022

    Fix test for LibreSSL

    ...

    d664b77

    Fix test_tls_version for LibreSSL

    ...

    5a2c5b9
11. CyberTailor

    added a commit that references this issue on Nov 29, 2022

    Fix test_tls_version for LibreSSL

    ...

    6299cd5
12. elprans

    added a commit that references this issue on Dec 3, 2022

    Fix test_tls_version for LibreSSL (#974)

    ...

    7df9812