dump the password used by an openssl client for its private key using LD_PRELOAD and hooking the callback registration functions

dumpprivatekeypassword.c

//
// based on https://git.lekensteyn.nl/peter/wireshark-notes/tree/src/
// Licensed under the terms of GPLv3 (or any later version) at your choice
//
// works for daemons which can be run in the foreground 
//
// gcc nccsslpasswdlog.c -shared -o nccsslpasswdlog.so -fPIC -ldl
//
//
 
#define _GNU_SOURCE
#include <dlfcn.h>
#include <openssl/ssl.h>
#include <fcntl.h>
#include <unistd.h>
#include <string.h>
#include <stdlib.h>
#include <stdio.h>
 
#ifndef OPENSSL_SONAME
#   define OPENSSL_SONAME   "libssl.so"
#endif
 
typedef int sslCB(char *buf, int size, int rwflag, void *password);
sslCB* funcsslCB = 0;
void* userData = 0;
 
static inline void *lookup_symbol(const char *sym)
{
    void *func = dlsym(RTLD_NEXT, sym);
    /* Symbol not found, OpenSSL is not loaded (linked) so try to load it
     * manually. This is error-prone as it depends on a fixed library name.
     * Perhaps it should be an env name? */
    if (!func) {
        void *handle = dlopen(OPENSSL_SONAME, RTLD_LAZY);
        if (!handle) {
            fprintf(stderr, "Lookup error for %s: %s", sym, dlerror());
            abort();
        }
        func = dlsym(handle, sym);
        if (!func) {
            fprintf(stderr, "Cannot lookup %s", sym);
            abort();
        }
        dlclose(handle);
    }
    return func;
}
 
 
void doit(void *u){
     char* strFoo=malloc(1024);
 
     memset(strFoo,0x00,1024);
     funcsslCB(strFoo,1024,0,u);
     fprintf(stderr,"password is '%s'\n",strFoo);
}
 
void SSL_CTX_set_default_passwd_cb(SSL_CTX *ctx, pem_password_cb *cb)
{
    fprintf(stderr,"%s called\n",__func__);
 
    static int (*func)();
    if (!func) {
        func = lookup_symbol(__func__);
    }
 
 
    funcsslCB = (sslCB*)cb;
 
    doit(userData);
 
    func(ctx,cb);
 
 
}
 
void SSL_CTX_set_default_passwd_cb_userdata(SSL_CTX *ctx, void *u)
{
    fprintf(stderr,"%s called\n",__func__);
 
    static int (*func)();
    if (!func) {
        func = lookup_symbol(__func__);
    }
 
    fprintf(stderr,"%08x\n",(int)u);
    userData = u;
 
    func(ctx, u);
}