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Merge pull request #7242 from geoffw0/sslquery
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‎cpp/change-notes/2021-11-25-certificate-result-conflation.md

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lgtm,codescanning
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* A new query `cpp/certificate-result-conflation` has been added for C/C++. The query flags unsafe use of OpenSSL and similar libraries.

‎cpp/ql/src/Security/CWE/CWE-295/SSLResultConflation.qhelp

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<!DOCTYPE qhelp PUBLIC
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"-//Semmle//qhelp//EN"
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"qhelp.dtd">
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<qhelp>
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<overview>
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<p>When checking the result of SSL certificate verification, accepting any error code may allow an attacker to impersonate someone who is trusted.</p>
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</overview>
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<recommendation>
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<p>When checking an SSL certificate with <code>SSL_get_verify_result</code>, only <code>X509_V_OK</code> is a success code. If there is any other result the certificate should not be accepted.</p>
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</recommendation>
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<example>
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<p>In this example the error code <code>X509_V_ERR_CERT_HAS_EXPIRED</code> is treated the same as an OK result. An expired certificate should not be accepted as it is more likely to be compromised than a valid certificate.</p>
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<sample src="SSLResultConflationBad.cpp" />
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<p>In the corrected example, only a result of <code>X509_V_OK</code> is accepted.</p>
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<sample src="SSLResultConflationGood.cpp" />
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</example>
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<references>
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</references>
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</qhelp>

‎cpp/ql/src/Security/CWE/CWE-295/SSLResultConflation.ql

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/**
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* @name Certificate result conflation
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* @description Only accept SSL certificates that pass certificate verification.
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* @kind problem
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* @problem.severity error
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* @security-severity 7.5
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* @precision medium
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* @id cpp/certificate-result-conflation
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* @tags security
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* external/cwe/cwe-295
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*/
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import cpp
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import semmle.code.cpp.controlflow.Guards
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import semmle.code.cpp.dataflow.DataFlow
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/**
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* A call to `SSL_get_verify_result`.
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*/
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class SSLGetVerifyResultCall extends FunctionCall {
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SSLGetVerifyResultCall() { getTarget().getName() = "SSL_get_verify_result" }
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}
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/**
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* Data flow from a call to `SSL_get_verify_result` to a guard condition
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* that references the result.
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*/
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class VerifyResultConfig extends DataFlow::Configuration {
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VerifyResultConfig() { this = "VerifyResultConfig" }
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override predicate isSource(DataFlow::Node source) {
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source.asExpr() instanceof SSLGetVerifyResultCall
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}
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override predicate isSink(DataFlow::Node sink) {
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exists(GuardCondition guard | guard.getAChild*() = sink.asExpr())
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}
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}
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from
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VerifyResultConfig config, DataFlow::Node source, DataFlow::Node sink1, DataFlow::Node sink2,
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GuardCondition guard, Expr c1, Expr c2, boolean testIsTrue
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where
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config.hasFlow(source, sink1) and
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config.hasFlow(source, sink2) and
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guard.comparesEq(sink1.asExpr(), c1, 0, false, testIsTrue) and // (value != c1) => testIsTrue
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guard.comparesEq(sink2.asExpr(), c2, 0, false, testIsTrue) and // (value != c2) => testIsTrue
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c1.getValue().toInt() = 0 and
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c2.getValue().toInt() != 0
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select guard, "This expression conflates OK and non-OK results from $@.", source, source.toString()

‎cpp/ql/src/Security/CWE/CWE-295/SSLResultConflationBad.cpp

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// ...
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if (cert = SSL_get_peer_certificate(ssl))
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{
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result = SSL_get_verify_result(ssl);
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if ((result == X509_V_OK) || (result == X509_V_ERR_CERT_HAS_EXPIRED)) // BAD (conflates OK and a non-OK codes)
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{
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do_ok();
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} else {
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do_error();
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}
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}

‎cpp/ql/src/Security/CWE/CWE-295/SSLResultConflationGood.cpp

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// ...
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if (cert = SSL_get_peer_certificate(ssl))
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{
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result = SSL_get_verify_result(ssl);
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if (result == X509_V_OK) // GOOD
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{
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do_ok();
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} else {
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do_error();
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}
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}

‎cpp/ql/test/query-tests/Security/CWE/CWE-295/SSLResultConflation.expected

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| test.cpp:18:9:18:38 | ... \|\| ... | This expression conflates OK and non-OK results from $@. | test.cpp:100:18:100:38 | call to SSL_get_verify_result | call to SSL_get_verify_result |
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| test.cpp:38:7:38:36 | ... \|\| ... | This expression conflates OK and non-OK results from $@. | test.cpp:36:16:36:36 | call to SSL_get_verify_result | call to SSL_get_verify_result |
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| test.cpp:54:7:54:47 | ... \|\| ... | This expression conflates OK and non-OK results from $@. | test.cpp:52:16:52:36 | call to SSL_get_verify_result | call to SSL_get_verify_result |
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| test.cpp:62:7:62:36 | ... \|\| ... | This expression conflates OK and non-OK results from $@. | test.cpp:60:16:60:36 | call to SSL_get_verify_result | call to SSL_get_verify_result |
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| test.cpp:70:7:70:36 | ... && ... | This expression conflates OK and non-OK results from $@. | test.cpp:68:16:68:36 | call to SSL_get_verify_result | call to SSL_get_verify_result |
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| test.cpp:83:7:83:40 | ... \|\| ... | This expression conflates OK and non-OK results from $@. | test.cpp:78:16:78:36 | call to SSL_get_verify_result | call to SSL_get_verify_result |
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| test.cpp:87:7:87:38 | ... \|\| ... | This expression conflates OK and non-OK results from $@. | test.cpp:7:57:7:77 | call to SSL_get_verify_result | call to SSL_get_verify_result |
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| test.cpp:107:13:107:42 | ... \|\| ... | This expression conflates OK and non-OK results from $@. | test.cpp:105:16:105:36 | call to SSL_get_verify_result | call to SSL_get_verify_result |

‎cpp/ql/test/query-tests/Security/CWE/CWE-295/SSLResultConflation.qlref

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Security/CWE/CWE-295/SSLResultConflation.ql

‎cpp/ql/test/query-tests/Security/CWE/CWE-295/test.cpp

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struct SSL {
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// ...
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};
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int SSL_get_verify_result(const SSL *ssl);
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int get_verify_result_indirect(const SSL *ssl) { return SSL_get_verify_result(ssl); }
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int something_else(const SSL *ssl);
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bool is_ok(int result)
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{
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return (result == 0); // GOOD
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}
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bool is_maybe_ok(int result)
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{
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return (result == 0) || (result == 1); // BAD (conflates OK and a non-OK codes)
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}
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void test1_1(SSL *ssl)
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{
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{
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int result = SSL_get_verify_result(ssl);
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if (result == 0) // GOOD
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{
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}
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if (result == 1) // GOOD
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{
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}
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}
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{
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int result = SSL_get_verify_result(ssl);
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if ((result == 0) || (result == 1)) // BAD (conflates OK and a non-OK codes)
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{
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}
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}
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{
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int result = SSL_get_verify_result(ssl);
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if ((result == 1) || (result == 2)) // GOOD (both results are non-OK)
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{
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}
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}
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{
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int result = SSL_get_verify_result(ssl);
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if ((result == 0) || (false) || (result == 2)) // BAD (conflates OK and a non-OK codes)
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{
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}
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}
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{
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int result = SSL_get_verify_result(ssl);
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if ((0 == result) || (1 == result)) // BAD (conflates OK and a non-OK codes)
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{
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}
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}
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{
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int result = SSL_get_verify_result(ssl);
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if ((result != 0) && (result != 1)) // BAD (conflates OK and a non-OK codes)
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{
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} else {
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// conflation occurs here
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}
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}
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{
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int result = SSL_get_verify_result(ssl);
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int result_cpy = result;
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int result2 = get_verify_result_indirect(ssl);
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int result3 = something_else(ssl);
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if ((result == 0) || (result_cpy == 1)) // BAD (conflates OK and a non-OK codes)
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{
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}
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if ((result2 == 0) || (result2 == 1)) // BAD (conflates OK and a non-OK codes)
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{
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}
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if ((result3 == 0) || (result3 == 1)) // GOOD (not an SSL result)
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{
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}
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}
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if (is_ok(SSL_get_verify_result(ssl)))
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{
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}
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if (is_maybe_ok(SSL_get_verify_result(ssl)))
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{
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}
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{
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int result = SSL_get_verify_result(ssl);
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bool ok = (result == 0) || (result == 1); // BAD (conflates OK and a non-OK codes)
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if (ok) {
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}
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}
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{
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int result = SSL_get_verify_result(ssl);
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if (result == 1) // BAD (conflates OK and a non-OK codes in `else`) [NOT DETECTED]
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{
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} else {
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}
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}
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}
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void do_good();
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void test1_2(SSL *ssl)
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{
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int result = SSL_get_verify_result(ssl);
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if (result == 0) { // GOOD
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do_good();
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} else if (result == 1) {
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throw 1;
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} else {
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throw 1;
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}
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}
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void test1_3(SSL *ssl)
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{
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int result = SSL_get_verify_result(ssl);
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if (result == 0) { // BAD (error code 1 is treated as OK, not as non-OK) [NOT DETECTED]
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do_good();
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} else if (result == 1) {
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do_good();
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} else {
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throw 1;
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}
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}

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