Segfault in Session::prepareCommonShared with proxy authentication

[simue]

Description

I get a segfault with the following call stack:

libc.so.6![Unknown/Just-In-Time compiled code] (Unknown Source:0)
Curl_setstropt(char ** charp, const char * s) (\home\user\.conan2\p\b\libcu0c6ab0202663c\b\src\lib\setopt.c:68)
Curl_vsetopt(struct Curl_easy * data, CURLoption option, va_list param) (\home\user\.conan2\p\b\libcu0c6ab0202663c\b\src\lib\setopt.c:1604)
curl_easy_setopt(struct Curl_easy * data, CURLoption tag) (\home\user\.conan2\p\b\libcu0c6ab0202663c\b\src\lib\setopt.c:3171)
cpr::Session::prepareCommonShared(cpr::Session * const this) (\home\user\repos\tmp\cpr\cpr\session.cpp:184)
cpr::Session::prepareCommon(cpr::Session * const this) (\home\user\repos\tmp\cpr\cpr\session.cpp:226)
cpr::Session::PreparePost(cpr::Session * const this) (\home\user\repos\tmp\cpr\cpr\session.cpp:860)
cpr::Session::Post(cpr::Session * const this) (\home\user\repos\tmp\cpr\cpr\session.cpp:748)
[...]

This happens when a proxy is set, along with proxy authentication.
Setting the proxy authentication manually in session.cpp resolved the issue for me:

    // Proxy:
    const std::string protocol = url_.str().substr(0, url_.str().find(':'));
    if (proxies_.has(protocol)) {
        curl_easy_setopt(curl_->handle, CURLOPT_PROXY, proxies_[protocol].c_str());
        if (proxyAuth_.has(protocol)) {
            // this worked:
            //  std::string username = "user";
            //  std::string password = "password";
            //  curl_easy_setopt(curl_->handle, CURLOPT_PROXYUSERNAME, username.c_str());
            //  curl_easy_setopt(curl_->handle, CURLOPT_PROXYPASSWORD, password.c_str());
            // this does trigger the segfault (original code):
            curl_easy_setopt(curl_->handle, CURLOPT_PROXYUSERNAME, proxyAuth_.GetUsername(protocol));
            curl_easy_setopt(curl_->handle, CURLOPT_PROXYPASSWORD, proxyAuth_.GetPassword(protocol));
        }
    }

Example/How to Reproduce

1. Create a cpr::Session
2. Set proxy with proxy authentication
3. Perform POST
4. Segfault

Possible Fix

I didn't look into that, yet

Where did you get it from?

GitHub (branch e.g. master)

Additional Context/Your Environment

• OS: Linux
• Version: custom kernel 5.15

[COM8]

@simue thanks for reporting.
Could you please create a small example application for me to reproduce this?

[simue]

#1181