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mbsync
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rewrite SSL certificate verification. again. 

leave all the hard work to OpenSSL. this has several consequences:
- certificate chain validation actually works instead of throwing
  around error 20
- the interactive approval is gone. i don't expect it to be useful
  anyway, as mbsync is mostly a batch tool
- the code is much shorter
wip/maildir-uid-dupes-test
Oswald Buddenhagen 12 years ago
parent
d00d38836d
commit
acb1c870b4
3 changed files with 60 additions and 134 deletions
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  1. 4
      src/isync.h
  2. 11
      src/mbsync.1
  3. 175
      src/socket.c

4
src/isync.h
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@ -67,8 +67,9 @@ typedef struct server_conf {
unsigned use_tlsv12:1;
/* these are actually variables and are leaked at the end */
unsigned ssl_ctx_valid:1;
unsigned num_trusted;
SSL_CTX *SSLContext;
X509_STORE *cert_store;
#endif
} server_conf_t;
@ -87,6 +88,7 @@ typedef struct {
char *name;
#ifdef HAVE_LIBSSL
SSL *ssl;
int force_trusted;
#endif
void (*bad_callback)( void *aux ); /* async fail while sending or listening */

11
src/mbsync.1
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@ -273,8 +273,12 @@ established with the IMAP server. (Default: \fIyes\fR)
..
.TP
\fBCertificateFile\fR \fIpath\fR
File containing X.509 CA certificates used to verify server identities.
This option is \fImandatory\fR if SSL is used. See \fBSSL CERTIFICATES\fR below.
File containing additional X.509 certificates used to verify server
identities. Directly matched peer certificates are always trusted,
regardless of validity.
.br
Note that the system's default certificate store is always used and should
not be specified here.
..
.TP
\fBUseSSLv2\fR \fIyes\fR|\fIno\fR
@ -507,9 +511,6 @@ disproportionate.
\fBThorough\fR - this avoids message duplication after crashes as well,
at some additional performance cost.
..
.SH SSL CERTIFICATES
[to be done]
..
.SH INHERENT PROBLEMS
Changes done after \fBmbsync\fR has retrieved the message list will not be
synchronised until the next time \fBmbsync\fR is invoked.

175
src/socket.c
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@ -62,6 +62,8 @@ socket_fail( conn_t *conn )
}
#ifdef HAVE_LIBSSL
static int ssl_data_idx;
static int
ssl_return( const char *func, conn_t *conn, int ret )
{
@ -99,26 +101,6 @@ ssl_return( const char *func, conn_t *conn, int ret )
/* Some of this code is inspired by / lifted from mutt. */
static int
compare_certificates( X509 *cert, X509 *peercert,
unsigned char *peermd, unsigned peermdlen )
{
unsigned char md[EVP_MAX_MD_SIZE];
unsigned mdlen;
/* Avoid CPU-intensive digest calculation if the certificates are
* not even remotely equal. */
if (X509_subject_name_cmp( cert, peercert ) ||
X509_issuer_name_cmp( cert, peercert ))
return -1;
if (!X509_digest( cert, EVP_sha1(), md, &mdlen ) ||
peermdlen != mdlen || memcmp( peermd, md, mdlen ))
return -1;
return 0;
}
static int
host_matches( const char *host, const char *pattern )
{
@ -175,120 +157,45 @@ verify_hostname( X509 *cert, const char *hostname )
return -1;
}
#if OPENSSL_VERSION_NUMBER >= 0x00904000L
#define READ_X509_KEY(fp, key) PEM_read_X509( fp, key, 0, 0 )
#else
#define READ_X509_KEY(fp, key) PEM_read_X509( fp, key, 0 )
#endif
/* this gets called when a certificate is to be verified */
static int
verify_cert( const server_conf_t *conf, conn_t *sock )
verify_cert_host( const server_conf_t *conf, conn_t *sock )
{
server_conf_t *mconf = (server_conf_t *)conf;
SSL *ssl = sock->ssl;
X509 *cert, *lcert;
BIO *bio;
FILE *fp;
int err;
unsigned n, i;
X509_STORE_CTX xsc;
char buf[256];
unsigned char md[EVP_MAX_MD_SIZE];
X509 *cert;
if (!conf->host || sock->force_trusted > 0)
return 0;
cert = SSL_get_peer_certificate( ssl );
cert = SSL_get_peer_certificate( sock->ssl );
if (!cert) {
error( "Error, no server certificate\n" );
return -1;
}
while (conf->cert_file) { /* while() instead of if() so break works */
/* Note: this code intentionally does no hostname verification. */
if (X509_cmp_current_time( X509_get_notBefore( cert )) >= 0) {
error( "Server certificate is not yet valid\n" );
break;
}
if (X509_cmp_current_time( X509_get_notAfter( cert )) <= 0) {
error( "Server certificate has expired\n" );
break;
}
if (!X509_digest( cert, EVP_sha1(), md, &n )) {
error( "*** Unable to calculate digest\n" );
break;
}
if (!(fp = fopen( conf->cert_file, "rt" ))) {
sys_error( "Unable to load CertificateFile '%s'", conf->cert_file );
return -1;
}
err = -1;
for (lcert = 0; READ_X509_KEY( fp, &lcert ); )
if (!(err = compare_certificates( lcert, cert, md, n ))) /* TODO: check X509v3 [Extended] Key Usage? */
break;
X509_free( lcert );
fclose( fp );
if (!err)
return 0;
break;
return verify_hostname( cert, conf->host );
}
if (!mconf->cert_store) {
if (!(mconf->cert_store = X509_STORE_new())) {
error( "Error creating certificate store\n" );
return -1;
}
if (!X509_STORE_set_default_paths( mconf->cert_store ))
warn( "Error while loading default certificate files: %s\n",
ERR_error_string( ERR_get_error(), 0 ) );
if (!conf->cert_file) {
info( "Note: CertificateFile not defined\n" );
} else if (!X509_STORE_load_locations( mconf->cert_store, conf->cert_file, 0 )) {
error( "Error while loading certificate file '%s': %s\n",
conf->cert_file, ERR_error_string( ERR_get_error(), 0 ) );
return -1;
}
static int
ssl_verify_callback( int ok, X509_STORE_CTX *ctx )
{
SSL *ssl = X509_STORE_CTX_get_ex_data( ctx, SSL_get_ex_data_X509_STORE_CTX_idx() );
conn_t *conn = SSL_get_ex_data( ssl, ssl_data_idx );
if (!conn->force_trusted) {
X509 *cert = sk_X509_value( ctx->chain, 0 );
STACK_OF(X509_OBJECT) *trusted = ctx->ctx->objs;
unsigned i;
conn->force_trusted = -1;
for (i = 0; i < conn->conf->num_trusted; i++) {
if (!X509_cmp( cert, sk_X509_OBJECT_value( trusted, i )->data.x509 )) {
conn->force_trusted = 1;
break;
}
X509_STORE_CTX_init( &xsc, mconf->cert_store, cert, 0 );
err = X509_verify_cert( &xsc ) > 0 ? 0 : X509_STORE_CTX_get_error( &xsc );
X509_STORE_CTX_cleanup( &xsc );
if (err) {
error( "Error, cannot verify certificate: %s (%d)\n",
X509_verify_cert_error_string( err ), err );
goto intcheck;
}
if (conf->host && verify_hostname( cert, conf->host ) < 0)
goto intcheck;
return 0;
intcheck:
X509_NAME_oneline( X509_get_subject_name( cert ), buf, sizeof(buf) );
info( "\nSubject: %s\n", buf );
X509_NAME_oneline( X509_get_issuer_name( cert ), buf, sizeof(buf) );
info( "Issuer: %s\n", buf );
bio = BIO_new( BIO_s_mem() );
ASN1_TIME_print( bio, X509_get_notBefore( cert ) );
memset( buf, 0, sizeof(buf) );
BIO_read( bio, buf, sizeof(buf) - 1 );
info( "Valid from: %s\n", buf );
ASN1_TIME_print( bio, X509_get_notAfter( cert ) );
memset( buf, 0, sizeof(buf) );
BIO_read( bio, buf, sizeof(buf) - 1 );
BIO_free( bio );
info( " to: %s\n", buf );
if (!X509_digest( cert, EVP_md5(), md, &n )) {
error( "*** Unable to calculate fingerprint\n" );
} else {
info( "Fingerprint: " );
for (i = 0; i < n; i += 2)
info( "%02X%02X ", md[i], md[i + 1] );
info( "\n" );
}
fputs( "\nAccept certificate? [y/N]: ", stderr );
if (fgets( buf, sizeof(buf), stdin ) && (buf[0] == 'y' || buf[0] == 'Y'))
return 0;
return -1;
if (conn->force_trusted > 0)
ok = 1;
return ok;
}
static int
@ -297,6 +204,9 @@ init_ssl_ctx( const server_conf_t *conf )
server_conf_t *mconf = (server_conf_t *)conf;
int options = 0;
if (conf->SSLContext)
return conf->ssl_ctx_valid;
mconf->SSLContext = SSL_CTX_new( SSLv23_client_method() );
if (!conf->use_sslv2)
@ -316,10 +226,21 @@ init_ssl_ctx( const server_conf_t *conf )
SSL_CTX_set_options( mconf->SSLContext, options );
/* we check the result of the verification after SSL_connect() */
SSL_CTX_set_verify( mconf->SSLContext, SSL_VERIFY_NONE, 0 );
if (conf->cert_file && !SSL_CTX_load_verify_locations( mconf->SSLContext, conf->cert_file, 0 )) {
error( "Error while loading certificate file '%s': %s\n",
conf->cert_file, ERR_error_string( ERR_get_error(), 0 ) );
return 0;
}
mconf->num_trusted = sk_X509_OBJECT_num( SSL_CTX_get_cert_store( mconf->SSLContext )->objs );
if (!SSL_CTX_set_default_verify_paths( mconf->SSLContext ))
warn( "Warning: Unable to load default certificate files: %s\n",
ERR_error_string( ERR_get_error(), 0 ) );
SSL_CTX_set_verify( mconf->SSLContext, SSL_VERIFY_PEER, ssl_verify_callback );
mconf->ssl_ctx_valid = 1;
return 1;
}
static void start_tls_p2( conn_t * );
static void start_tls_p3( conn_t *, int );
@ -334,10 +255,11 @@ socket_start_tls( conn_t *conn, void (*cb)( int ok, void *aux ) )
if (!ssl_inited) {
SSL_library_init();
SSL_load_error_strings();
ssl_data_idx = SSL_get_ex_new_index( 0, NULL, NULL, NULL, NULL );
ssl_inited = 1;
}
if (!conn->conf->SSLContext && init_ssl_ctx( conn->conf )) {
if (!init_ssl_ctx( conn->conf )) {
start_tls_p3( conn, 0 );
return;
}
@ -345,6 +267,7 @@ socket_start_tls( conn_t *conn, void (*cb)( int ok, void *aux ) )
conn->ssl = SSL_new( ((server_conf_t *)conn->conf)->SSLContext );
SSL_set_fd( conn->ssl, conn->fd );
SSL_set_mode( conn->ssl, SSL_MODE_ACCEPT_MOVING_WRITE_BUFFER );
SSL_set_ex_data( conn->ssl, ssl_data_idx, conn );
conn->state = SCK_STARTTLS;
start_tls_p2( conn );
}
@ -359,8 +282,8 @@ start_tls_p2( conn_t *conn )
case 0:
break;
default:
/* verify the server certificate */
if (verify_cert( conn->conf, conn )) {
/* verify whether the server hostname matches the certificate */
if (verify_cert_host( conn->conf, conn )) {
start_tls_p3( conn, 0 );
} else {
info( "Connection is now encrypted\n" );

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