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Adding initial pkcs#11 support for TLS private key storage #436

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Adding initial pkcs#11 support for TLS private key storage #436

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56 changes: 53 additions & 3 deletions src/session_client_tls.c
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Original file line number Diff line number Diff line change
Expand Up @@ -22,6 +22,7 @@
#include <errno.h>
#include <string.h>
#include <unistd.h>
#include <openssl/engine.h>

#include <libyang/libyang.h>
#include <openssl/err.h>
Expand Down Expand Up @@ -508,6 +509,10 @@ nc_client_tls_update_opts(struct nc_client_tls_opts *opts, const char *peername)
char *key;
X509_LOOKUP *lookup;
X509_VERIFY_PARAM *vpm = NULL;
const int CMD_MANDATORY = 0;
EVP_PKEY *pkey = NULL;
ENGINE * pkcs11 = NULL;
const char* opensc_pkcs11_so = getenv("MODULE");

if (!opts->tls_ctx || opts->tls_ctx_change) {
SSL_CTX_free(opts->tls_ctx);
Expand Down Expand Up @@ -540,13 +545,57 @@ nc_client_tls_update_opts(struct nc_client_tls_opts *opts, const char *peername)
} else {
key = opts->key_path;
}
if (SSL_CTX_use_PrivateKey_file(opts->tls_ctx, key, SSL_FILETYPE_PEM) != 1) {
ERR(NULL, "Loading the client private key from \'%s\' failed (%s).", key,
ERR_reason_error_string(ERR_get_error()));

ENGINE_load_dynamic();
pkcs11 = ENGINE_by_id( "pkcs11" );
if ( pkcs11 == NULL )
{
ERR(NULL, "Error retrieving 'pkcs11' engine");
rc = -1;
goto cleanup;
Comment on lines +553 to +555
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This means that the code would hard-fail at runtime when OpenSSL is built without this dynamic engine support. It's better to only request a dynamic engine when needed, i.e., hide this behind some switch to active this new functionality.

The library should continue to work as-is when the user does not opt-in to this new feature (which by definition requires some configuration).

}

if ( 0 != access( opensc_pkcs11_so, R_OK ) )
{
ERR(NULL, "Error finding '/usr/local/lib/libpkcs11-proxy.so'");
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paths cannot be hardcoded like that, not even in error messages

rc = -1;
goto cleanup;
}

if ( 1 != ENGINE_ctrl_cmd_string( pkcs11, "MODULE_PATH", opensc_pkcs11_so, CMD_MANDATORY ) )
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This loads a .so into the process' address space based on a an environment variable. That's effectively an arbitrary code execution vulnerability based on a non-standard variable name.

How does OpenSSL typically solve this?

Also, the README upstream says that the command name is called SO_PATH, not MODULE_PATH.

{
ERR(NULL, "Error setting module_path <= '/usr/local/lib/libpkcs11-proxy.so'");
rc = -1;
goto cleanup;
}

if ( 1 != ENGINE_init( pkcs11 ) )
{
ERR(NULL, "Error pkcs11: unable to initialize engine");
rc = -1;
goto cleanup;
}

if ( 1 != ENGINE_ctrl_cmd_string( pkcs11, "PIN", "1234", CMD_MANDATORY ) )
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a hardcoded PIN?

{
ERR(NULL, "Error setting pin");
rc = -1;
goto cleanup;
}

pkey = ENGINE_load_private_key( pkcs11, key, NULL, NULL );
if (!key)
{
ERR(NULL, "Error reading private key");
rc = -1;
goto cleanup;
}
if ((SSL_CTX_use_PrivateKey(opts->tls_ctx, pkey) != 1))
{
ERR(NULL, "Loading the client private key failed (%s).", ERR_reason_error_string(ERR_get_error()));
rc = -1;
goto cleanup;
}
if (!SSL_CTX_load_verify_locations(opts->tls_ctx, opts->ca_file, opts->ca_dir)) {
ERR(NULL, "Failed to load the locations of trusted CA certificates (%s).",
ERR_reason_error_string(ERR_get_error()));
Expand Down Expand Up @@ -617,6 +666,7 @@ nc_client_tls_update_opts(struct nc_client_tls_opts *opts, const char *peername)

cleanup:
X509_VERIFY_PARAM_free(vpm);
EVP_PKEY_free(pkey);
return rc;
}

Expand Down
70 changes: 60 additions & 10 deletions src/session_server_tls.c
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Original file line number Diff line number Diff line change
Expand Up @@ -18,6 +18,7 @@
#include <poll.h>
#include <string.h>
#include <unistd.h>
#include <openssl/engine.h>

#include <openssl/err.h>
#include <openssl/evp.h>
Expand Down Expand Up @@ -1748,7 +1749,12 @@ nc_tls_ctx_set_server_cert_key(SSL_CTX *tls_ctx, const char *cert_name)
int ret = 0;
NC_SSH_KEY_TYPE privkey_type;
X509 *cert = NULL;
EVP_PKEY *pkey = NULL;
EVP_PKEY *key = NULL;
ENGINE * pkcs11 = NULL;
const int CMD_MANDATORY = 0;
const char* opensc_pkcs11_so = getenv("MODULE");
const char* uri = getenv("TOKEN_KEY_URI");
const char* pin = getenv("DEFAULT_USER_PIN");

if (!cert_name) {
ERR(NULL, "Server certificate not set.");
Expand Down Expand Up @@ -1781,26 +1787,70 @@ nc_tls_ctx_set_server_cert_key(SSL_CTX *tls_ctx, const char *cert_name)
}

/* load the private key */
if (privkey_path) {
if (SSL_CTX_use_PrivateKey_file(tls_ctx, privkey_path, SSL_FILETYPE_PEM) != 1) {
ERR(NULL, "Loading the server private key failed (%s).", ERR_reason_error_string(ERR_get_error()));
if (privkey_path) {
if (SSL_CTX_use_PrivateKey_file(tls_ctx, privkey_path, SSL_FILETYPE_PEM) != 1) {
ERR(NULL, "1 Loading the server private key failed (%s).", ERR_reason_error_string(ERR_get_error()));
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nit: extra 1 ?

ret = -1;
goto cleanup;
}
} else {

ENGINE_load_dynamic();
pkcs11 = ENGINE_by_id( "pkcs11" );
if ( pkcs11 == NULL )
{
ERR(NULL, "Error retrieving 'pkcs11' engine");
ret = -1;
goto cleanup;
}
} else {
pkey = base64der_to_privatekey(privkey_data, nc_keytype2str(privkey_type));
if (!pkey || (SSL_CTX_use_PrivateKey(tls_ctx, pkey) != 1)) {
ERR(NULL, "Loading the server private key failed (%s).", ERR_reason_error_string(ERR_get_error()));

if ( 0 != access( opensc_pkcs11_so, R_OK ) )
{
ERR(NULL, "Error finding pkcs module");
ret = -1;
goto cleanup;
}

if ( 1 != ENGINE_ctrl_cmd_string( pkcs11, "MODULE_PATH", opensc_pkcs11_so, CMD_MANDATORY ) )
{
ERR(NULL, "Error setting module_path");
ret = -1;
goto cleanup;
}

if ( 1 != ENGINE_init( pkcs11 ) )
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The documentation says:

This returns zero if the ENGINE was not already operational and couldn't be successfully initialised (e.g. lack of system drivers, no special hardware attached, etc), otherwise it will return nonzero to indicate that the ENGINE is now operational and will have allocated a new functional reference to the ENGINE.

...yet the code checks for 1.

Also everywhere else.

{
ERR(NULL, "Error pkcs11: unable to initialize engine");
ret = -1;
goto cleanup;
}
}

if ( 1 != ENGINE_ctrl_cmd_string( pkcs11, "PIN", pin, CMD_MANDATORY ) )
{
ERR(NULL, "Error setting pin");
ret = -1;
goto cleanup;
}

key = ENGINE_load_private_key( pkcs11, uri, NULL, NULL );
if (!key)
{
ERR(NULL, "Error reading private key using uri");
ret = -1;
goto cleanup;
}

if ((SSL_CTX_use_PrivateKey(tls_ctx, key) != 1)) {
ERR(NULL, "Loading the server private key failed (%s).", ERR_reason_error_string(ERR_get_error()));
ret = -1;
goto cleanup;
}
}
ret = nc_tls_ctx_set_server_cert_chain(tls_ctx, cert_name);

cleanup:
X509_free(cert);
EVP_PKEY_free(pkey);
EVP_PKEY_free(key);
free(cert_path);
free(cert_data);
free(privkey_path);
Expand Down