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putty-source/windows/wingss.c
Simon Tatham d515e4f1a3 Support GSS key exchange, for Kerberos 5 only. 
This is a heavily edited (by me) version of a patch originally due to
Nico Williams and Viktor Dukhovni. Their comments:

 * Don't delegate credentials when rekeying unless there's a new TGT
   or the old service ticket is nearly expired.

 * Check for the above conditions more frequently (every two minutes
   by default) and rekey when we would delegate credentials.

 * Do not rekey with very short service ticket lifetimes; some GSSAPI
   libraries may lose the race to use an almost expired ticket. Adjust
   the timing of rekey checks to try to avoid this possibility.

My further comments:

The most interesting thing about this patch to me is that the use of
GSS key exchange causes a switch over to a completely different model
of what host keys are for. This comes from RFC 4462 section 2.1: the
basic idea is that when your session is mostly bidirectionally
authenticated by the GSSAPI exchanges happening in initial kex and
every rekey, host keys become more or less vestigial, and their
remaining purpose is to allow a rekey to happen if the requirements of
the SSH protocol demand it at an awkward moment when the GSS
credentials are not currently available (e.g. timed out and haven't
been renewed yet). As such, there's no need for host keys to be
_permanent_ or to be a reliable identifier of a particular host, and
RFC 4462 allows for the possibility that they might be purely
transient and only for this kind of emergency fallback purpose.

Therefore, once PuTTY has done a GSS key exchange, it disconnects
itself completely from the permanent host key cache functions in
storage.h, and instead switches to a _transient_ host key cache stored
in memory with the lifetime of just that SSH session. That cache is
populated with keys received from the server as a side effect of GSS
kex (via the optional SSH2_MSG_KEXGSS_HOSTKEY message), and used if
later in the session we have to fall back to a non-GSS key exchange.
However, in practice servers we've tested against do not send a host
key in that way, so we also have a fallback method of populating the
transient cache by triggering an immediate non-GSS rekey straight
after userauth (reusing the code path we also use to turn on OpenSSH
delayed encryption without the race condition).
2018-04-26 07:21:16 +01:00

642 lines
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#ifndef NO_GSSAPI
#include <limits.h>
#include "putty.h"
#define SECURITY_WIN32
#include <security.h>
#include "pgssapi.h"
#include "sshgss.h"
#include "sshgssc.h"
#include "misc.h"
#define UNIX_EPOCH 11644473600ULL /* Seconds from Windows epoch */
#define CNS_PERSEC 10000000ULL /* # 100ns per second */
/*
* Note, as a special case, 0 relative to the Windows epoch (unspecified) maps
* to 0 relative to the POSIX epoch (unspecified)!
*/
#define TIME_WIN_TO_POSIX(ft, t) do { \
ULARGE_INTEGER uli; \
uli.LowPart = (ft).dwLowDateTime; \
uli.HighPart = (ft).dwHighDateTime; \
if (uli.QuadPart != 0) \
uli.QuadPart = uli.QuadPart / CNS_PERSEC - UNIX_EPOCH; \
(t) = (time_t) uli.QuadPart; \
} while(0)
/* Windows code to set up the GSSAPI library list. */
#ifdef _WIN64
#define MIT_KERB_SUFFIX "64"
#else
#define MIT_KERB_SUFFIX "32"
#endif
const int ngsslibs = 3;
const char *const gsslibnames[3] = {
"MIT Kerberos GSSAPI"MIT_KERB_SUFFIX".DLL",
"Microsoft SSPI SECUR32.DLL",
"User-specified GSSAPI DLL",
};
const struct keyvalwhere gsslibkeywords[] = {
{ "gssapi32", 0, -1, -1 },
{ "sspi", 1, -1, -1 },
{ "custom", 2, -1, -1 },
};
DECL_WINDOWS_FUNCTION(static, SECURITY_STATUS,
AcquireCredentialsHandleA,
(SEC_CHAR *, SEC_CHAR *, ULONG, PVOID,
PVOID, SEC_GET_KEY_FN, PVOID, PCredHandle, PTimeStamp));
DECL_WINDOWS_FUNCTION(static, SECURITY_STATUS,
InitializeSecurityContextA,
(PCredHandle, PCtxtHandle, SEC_CHAR *, ULONG, ULONG,
ULONG, PSecBufferDesc, ULONG, PCtxtHandle,
PSecBufferDesc, PULONG, PTimeStamp));
DECL_WINDOWS_FUNCTION(static, SECURITY_STATUS,
FreeContextBuffer,
(PVOID));
DECL_WINDOWS_FUNCTION(static, SECURITY_STATUS,
FreeCredentialsHandle,
(PCredHandle));
DECL_WINDOWS_FUNCTION(static, SECURITY_STATUS,
DeleteSecurityContext,
(PCtxtHandle));
DECL_WINDOWS_FUNCTION(static, SECURITY_STATUS,
QueryContextAttributesA,
(PCtxtHandle, ULONG, PVOID));
DECL_WINDOWS_FUNCTION(static, SECURITY_STATUS,
MakeSignature,
(PCtxtHandle, ULONG, PSecBufferDesc, ULONG));
DECL_WINDOWS_FUNCTION(static, SECURITY_STATUS,
VerifySignature,
(PCtxtHandle, PSecBufferDesc, ULONG, PULONG));
DECL_WINDOWS_FUNCTION(static, DLL_DIRECTORY_COOKIE,
AddDllDirectory,
(PCWSTR));
typedef struct winSsh_gss_ctx {
unsigned long maj_stat;
unsigned long min_stat;
CredHandle cred_handle;
CtxtHandle context;
PCtxtHandle context_handle;
TimeStamp expiry;
} winSsh_gss_ctx;
const Ssh_gss_buf gss_mech_krb5={9,"\x2A\x86\x48\x86\xF7\x12\x01\x02\x02"};
const char *gsslogmsg = NULL;
static void ssh_sspi_bind_fns(struct ssh_gss_library *lib);
struct ssh_gss_liblist *ssh_gss_setup(Conf *conf)
{
HMODULE module;
HKEY regkey;
struct ssh_gss_liblist *list = snew(struct ssh_gss_liblist);
char *path;
static HMODULE kernel32_module;
if (!kernel32_module) {
kernel32_module = load_system32_dll("kernel32.dll");
}
#if defined _MSC_VER && _MSC_VER < 1900
/* Omit the type-check because older MSVCs don't have this function */
GET_WINDOWS_FUNCTION_NO_TYPECHECK(kernel32_module, AddDllDirectory);
#else
GET_WINDOWS_FUNCTION(kernel32_module, AddDllDirectory);
#endif
list->libraries = snewn(3, struct ssh_gss_library);
list->nlibraries = 0;
/* MIT Kerberos GSSAPI implementation */
module = NULL;
if (RegOpenKey(HKEY_LOCAL_MACHINE, "SOFTWARE\\MIT\\Kerberos", &regkey)
== ERROR_SUCCESS) {
DWORD type, size;
LONG ret;
char *buffer;
/* Find out the string length */
ret = RegQueryValueEx(regkey, "InstallDir", NULL, &type, NULL, &size);
if (ret == ERROR_SUCCESS && type == REG_SZ) {
buffer = snewn(size + 20, char);
ret = RegQueryValueEx(regkey, "InstallDir", NULL,
&type, (LPBYTE)buffer, &size);
if (ret == ERROR_SUCCESS && type == REG_SZ) {
strcat (buffer, "\\bin");
if(p_AddDllDirectory) {
/* Add MIT Kerberos' path to the DLL search path,
* it loads its own DLLs further down the road */
wchar_t *dllPath =
dup_mb_to_wc(DEFAULT_CODEPAGE, 0, buffer);
p_AddDllDirectory(dllPath);
sfree(dllPath);
}
strcat (buffer, "\\gssapi"MIT_KERB_SUFFIX".dll");
module = LoadLibraryEx (buffer, NULL,
LOAD_LIBRARY_SEARCH_SYSTEM32 |
LOAD_LIBRARY_SEARCH_DLL_LOAD_DIR |
LOAD_LIBRARY_SEARCH_USER_DIRS);
}
sfree(buffer);
}
RegCloseKey(regkey);
}
if (module) {
struct ssh_gss_library *lib =
&list->libraries[list->nlibraries++];
lib->id = 0;
lib->gsslogmsg = "Using GSSAPI from GSSAPI"MIT_KERB_SUFFIX".DLL";
lib->handle = (void *)module;
#define BIND_GSS_FN(name) \
lib->u.gssapi.name = (t_gss_##name) GetProcAddress(module, "gss_" #name)
BIND_GSS_FN(delete_sec_context);
BIND_GSS_FN(display_status);
BIND_GSS_FN(get_mic);
BIND_GSS_FN(verify_mic);
BIND_GSS_FN(import_name);
BIND_GSS_FN(init_sec_context);
BIND_GSS_FN(release_buffer);
BIND_GSS_FN(release_cred);
BIND_GSS_FN(release_name);
#undef BIND_GSS_FN
ssh_gssapi_bind_fns(lib);
}
/* Microsoft SSPI Implementation */
module = load_system32_dll("secur32.dll");
if (module) {
struct ssh_gss_library *lib =
&list->libraries[list->nlibraries++];
lib->id = 1;
lib->gsslogmsg = "Using SSPI from SECUR32.DLL";
lib->handle = (void *)module;
GET_WINDOWS_FUNCTION(module, AcquireCredentialsHandleA);
GET_WINDOWS_FUNCTION(module, InitializeSecurityContextA);
GET_WINDOWS_FUNCTION(module, FreeContextBuffer);
GET_WINDOWS_FUNCTION(module, FreeCredentialsHandle);
GET_WINDOWS_FUNCTION(module, DeleteSecurityContext);
GET_WINDOWS_FUNCTION(module, QueryContextAttributesA);
GET_WINDOWS_FUNCTION(module, MakeSignature);
GET_WINDOWS_FUNCTION(module, VerifySignature);
ssh_sspi_bind_fns(lib);
}
/*
* Custom GSSAPI DLL.
*/
module = NULL;
path = conf_get_filename(conf, CONF_ssh_gss_custom)->path;
if (*path) {
if(p_AddDllDirectory) {
/* Add the custom directory as well in case it chainloads
* some other DLLs (e.g a non-installed MIT Kerberos
* instance) */
int pathlen = strlen(path);
while (pathlen > 0 && path[pathlen-1] != ':' &&
path[pathlen-1] != '\\')
pathlen--;
if (pathlen > 0 && path[pathlen-1] != '\\')
pathlen--;
if (pathlen > 0) {
char *dirpath = dupprintf("%.*s", pathlen, path);
wchar_t *dllPath = dup_mb_to_wc(DEFAULT_CODEPAGE, 0, dirpath);
p_AddDllDirectory(dllPath);
sfree(dllPath);
sfree(dirpath);
}
}
module = LoadLibraryEx(path, NULL,
LOAD_LIBRARY_SEARCH_SYSTEM32 |
LOAD_LIBRARY_SEARCH_DLL_LOAD_DIR |
LOAD_LIBRARY_SEARCH_USER_DIRS);
}
if (module) {
struct ssh_gss_library *lib =
&list->libraries[list->nlibraries++];
lib->id = 2;
lib->gsslogmsg = dupprintf("Using GSSAPI from user-specified"
" library '%s'", path);
lib->handle = (void *)module;
#define BIND_GSS_FN(name) \
lib->u.gssapi.name = (t_gss_##name) GetProcAddress(module, "gss_" #name)
BIND_GSS_FN(delete_sec_context);
BIND_GSS_FN(display_status);
BIND_GSS_FN(get_mic);
BIND_GSS_FN(verify_mic);
BIND_GSS_FN(import_name);
BIND_GSS_FN(init_sec_context);
BIND_GSS_FN(release_buffer);
BIND_GSS_FN(release_cred);
BIND_GSS_FN(release_name);
#undef BIND_GSS_FN
ssh_gssapi_bind_fns(lib);
}
return list;
}
void ssh_gss_cleanup(struct ssh_gss_liblist *list)
{
int i;
/*
* LoadLibrary and FreeLibrary are defined to employ reference
* counting in the case where the same library is repeatedly
* loaded, so even in a multiple-sessions-per-process context
* (not that we currently expect ever to have such a thing on
* Windows) it's safe to naively FreeLibrary everything here
* without worrying about destroying it under the feet of
* another SSH instance still using it.
*/
for (i = 0; i < list->nlibraries; i++) {
FreeLibrary((HMODULE)list->libraries[i].handle);
if (list->libraries[i].id == 2) {
/* The 'custom' id involves a dynamically allocated message.
* Note that we must cast away the 'const' to free it. */
sfree((char *)list->libraries[i].gsslogmsg);
}
}
sfree(list->libraries);
sfree(list);
}
static Ssh_gss_stat ssh_sspi_indicate_mech(struct ssh_gss_library *lib,
Ssh_gss_buf *mech)
{
*mech = gss_mech_krb5;
return SSH_GSS_OK;
}
static Ssh_gss_stat ssh_sspi_import_name(struct ssh_gss_library *lib,
char *host, Ssh_gss_name *srv_name)
{
char *pStr;
/* Check hostname */
if (host == NULL) return SSH_GSS_FAILURE;
/* copy it into form host/FQDN */
pStr = dupcat("host/", host, NULL);
*srv_name = (Ssh_gss_name) pStr;
return SSH_GSS_OK;
}
static Ssh_gss_stat ssh_sspi_acquire_cred(struct ssh_gss_library *lib,
Ssh_gss_ctx *ctx,
time_t *expiry)
{
winSsh_gss_ctx *winctx = snew(winSsh_gss_ctx);
memset(winctx, 0, sizeof(winSsh_gss_ctx));
/* prepare our "wrapper" structure */
winctx->maj_stat = winctx->min_stat = SEC_E_OK;
winctx->context_handle = NULL;
/* Specifying no principal name here means use the credentials of
the current logged-in user */
winctx->maj_stat = p_AcquireCredentialsHandleA(NULL,
"Kerberos",
SECPKG_CRED_OUTBOUND,
NULL,
NULL,
NULL,
NULL,
&winctx->cred_handle,
NULL);
if (winctx->maj_stat != SEC_E_OK) {
p_FreeCredentialsHandle(&winctx->cred_handle);
sfree(winctx);
return SSH_GSS_FAILURE;
}
/* Windows does not return a valid expiration from AcquireCredentials */
if (expiry)
*expiry = GSS_NO_EXPIRATION;
*ctx = (Ssh_gss_ctx) winctx;
return SSH_GSS_OK;
}
static void localexp_to_exp_lifetime(TimeStamp *localexp,
time_t *expiry, unsigned long *lifetime)
{
FILETIME nowUTC;
FILETIME expUTC;
time_t now;
time_t exp;
time_t delta;
if (!lifetime && !expiry)
return;
GetSystemTimeAsFileTime(&nowUTC);
TIME_WIN_TO_POSIX(nowUTC, now);
if (lifetime)
*lifetime = 0;
if (expiry)
*expiry = GSS_NO_EXPIRATION;
if (!LocalFileTimeToFileTime(localexp, &expUTC))
return;
TIME_WIN_TO_POSIX(expUTC, exp);
delta = exp - now;
if (exp == 0 || delta <= 0)
return;
if (expiry)
*expiry = exp;
if (lifetime) {
if (delta <= ULONG_MAX)
*lifetime = (unsigned long)delta;
else
*lifetime = ULONG_MAX;
}
}
static Ssh_gss_stat ssh_sspi_init_sec_context(struct ssh_gss_library *lib,
Ssh_gss_ctx *ctx,
Ssh_gss_name srv_name,
int to_deleg,
Ssh_gss_buf *recv_tok,
Ssh_gss_buf *send_tok,
time_t *expiry,
unsigned long *lifetime)
{
winSsh_gss_ctx *winctx = (winSsh_gss_ctx *) *ctx;
SecBuffer wsend_tok = {send_tok->length,SECBUFFER_TOKEN,send_tok->value};
SecBuffer wrecv_tok = {recv_tok->length,SECBUFFER_TOKEN,recv_tok->value};
SecBufferDesc output_desc={SECBUFFER_VERSION,1,&wsend_tok};
SecBufferDesc input_desc ={SECBUFFER_VERSION,1,&wrecv_tok};
unsigned long flags=ISC_REQ_MUTUAL_AUTH|ISC_REQ_REPLAY_DETECT|
ISC_REQ_CONFIDENTIALITY|ISC_REQ_ALLOCATE_MEMORY;
unsigned long ret_flags=0;
TimeStamp localexp;
/* check if we have to delegate ... */
if (to_deleg) flags |= ISC_REQ_DELEGATE;
winctx->maj_stat = p_InitializeSecurityContextA(&winctx->cred_handle,
winctx->context_handle,
(char*) srv_name,
flags,
0, /* reserved */
SECURITY_NATIVE_DREP,
&input_desc,
0, /* reserved */
&winctx->context,
&output_desc,
&ret_flags,
&localexp);
localexp_to_exp_lifetime(&localexp, expiry, lifetime);
/* prepare for the next round */
winctx->context_handle = &winctx->context;
send_tok->value = wsend_tok.pvBuffer;
send_tok->length = wsend_tok.cbBuffer;
/* check & return our status */
if (winctx->maj_stat==SEC_E_OK) return SSH_GSS_S_COMPLETE;
if (winctx->maj_stat==SEC_I_CONTINUE_NEEDED) return SSH_GSS_S_CONTINUE_NEEDED;
return SSH_GSS_FAILURE;
}
static Ssh_gss_stat ssh_sspi_free_tok(struct ssh_gss_library *lib,
Ssh_gss_buf *send_tok)
{
/* check input */
if (send_tok == NULL) return SSH_GSS_FAILURE;
/* free Windows buffer */
p_FreeContextBuffer(send_tok->value);
SSH_GSS_CLEAR_BUF(send_tok);
return SSH_GSS_OK;
}
static Ssh_gss_stat ssh_sspi_release_cred(struct ssh_gss_library *lib,
Ssh_gss_ctx *ctx)
{
winSsh_gss_ctx *winctx= (winSsh_gss_ctx *) *ctx;
/* check input */
if (winctx == NULL) return SSH_GSS_FAILURE;
/* free Windows data */
p_FreeCredentialsHandle(&winctx->cred_handle);
p_DeleteSecurityContext(&winctx->context);
/* delete our "wrapper" structure */
sfree(winctx);
*ctx = (Ssh_gss_ctx) NULL;
return SSH_GSS_OK;
}
static Ssh_gss_stat ssh_sspi_release_name(struct ssh_gss_library *lib,
Ssh_gss_name *srv_name)
{
char *pStr= (char *) *srv_name;
if (pStr == NULL) return SSH_GSS_FAILURE;
sfree(pStr);
*srv_name = (Ssh_gss_name) NULL;
return SSH_GSS_OK;
}
static Ssh_gss_stat ssh_sspi_display_status(struct ssh_gss_library *lib,
Ssh_gss_ctx ctx, Ssh_gss_buf *buf)
{
winSsh_gss_ctx *winctx = (winSsh_gss_ctx *) ctx;
const char *msg;
if (winctx == NULL) return SSH_GSS_FAILURE;
/* decode the error code */
switch (winctx->maj_stat) {
case SEC_E_OK: msg="SSPI status OK"; break;
case SEC_E_INVALID_HANDLE: msg="The handle passed to the function"
" is invalid.";
break;
case SEC_E_TARGET_UNKNOWN: msg="The target was not recognized."; break;
case SEC_E_LOGON_DENIED: msg="The logon failed."; break;
case SEC_E_INTERNAL_ERROR: msg="The Local Security Authority cannot"
" be contacted.";
break;
case SEC_E_NO_CREDENTIALS: msg="No credentials are available in the"
" security package.";
break;
case SEC_E_NO_AUTHENTICATING_AUTHORITY:
msg="No authority could be contacted for authentication."
"The domain name of the authenticating party could be wrong,"
" the domain could be unreachable, or there might have been"
" a trust relationship failure.";
break;
case SEC_E_INSUFFICIENT_MEMORY:
msg="One or more of the SecBufferDesc structures passed as"
" an OUT parameter has a buffer that is too small.";
break;
case SEC_E_INVALID_TOKEN:
msg="The error is due to a malformed input token, such as a"
" token corrupted in transit, a token"
" of incorrect size, or a token passed into the wrong"
" security package. Passing a token to"
" the wrong package can happen if client and server did not"
" negotiate the proper security package.";
break;
default:
msg = "Internal SSPI error";
break;
}
buf->value = dupstr(msg);
buf->length = strlen(buf->value);
return SSH_GSS_OK;
}
static Ssh_gss_stat ssh_sspi_get_mic(struct ssh_gss_library *lib,
Ssh_gss_ctx ctx, Ssh_gss_buf *buf,
Ssh_gss_buf *hash)
{
winSsh_gss_ctx *winctx= (winSsh_gss_ctx *) ctx;
SecPkgContext_Sizes ContextSizes;
SecBufferDesc InputBufferDescriptor;
SecBuffer InputSecurityToken[2];
if (winctx == NULL) return SSH_GSS_FAILURE;
winctx->maj_stat = 0;
memset(&ContextSizes, 0, sizeof(ContextSizes));
winctx->maj_stat = p_QueryContextAttributesA(&winctx->context,
SECPKG_ATTR_SIZES,
&ContextSizes);
if (winctx->maj_stat != SEC_E_OK ||
ContextSizes.cbMaxSignature == 0)
return winctx->maj_stat;
InputBufferDescriptor.cBuffers = 2;
InputBufferDescriptor.pBuffers = InputSecurityToken;
InputBufferDescriptor.ulVersion = SECBUFFER_VERSION;
InputSecurityToken[0].BufferType = SECBUFFER_DATA;
InputSecurityToken[0].cbBuffer = buf->length;
InputSecurityToken[0].pvBuffer = buf->value;
InputSecurityToken[1].BufferType = SECBUFFER_TOKEN;
InputSecurityToken[1].cbBuffer = ContextSizes.cbMaxSignature;
InputSecurityToken[1].pvBuffer = snewn(ContextSizes.cbMaxSignature, char);
winctx->maj_stat = p_MakeSignature(&winctx->context,
0,
&InputBufferDescriptor,
0);
if (winctx->maj_stat == SEC_E_OK) {
hash->length = InputSecurityToken[1].cbBuffer;
hash->value = InputSecurityToken[1].pvBuffer;
}
return winctx->maj_stat;
}
static Ssh_gss_stat ssh_sspi_verify_mic(struct ssh_gss_library *lib,
Ssh_gss_ctx ctx,
Ssh_gss_buf *buf,
Ssh_gss_buf *mic)
{
winSsh_gss_ctx *winctx= (winSsh_gss_ctx *) ctx;
SecBufferDesc InputBufferDescriptor;
SecBuffer InputSecurityToken[2];
ULONG qop;
if (winctx == NULL) return SSH_GSS_FAILURE;
winctx->maj_stat = 0;
InputBufferDescriptor.cBuffers = 2;
InputBufferDescriptor.pBuffers = InputSecurityToken;
InputBufferDescriptor.ulVersion = SECBUFFER_VERSION;
InputSecurityToken[0].BufferType = SECBUFFER_DATA;
InputSecurityToken[0].cbBuffer = buf->length;
InputSecurityToken[0].pvBuffer = buf->value;
InputSecurityToken[1].BufferType = SECBUFFER_TOKEN;
InputSecurityToken[1].cbBuffer = mic->length;
InputSecurityToken[1].pvBuffer = mic->value;
winctx->maj_stat = p_VerifySignature(&winctx->context,
&InputBufferDescriptor,
0, &qop);
return winctx->maj_stat;
}
static Ssh_gss_stat ssh_sspi_free_mic(struct ssh_gss_library *lib,
Ssh_gss_buf *hash)
{
sfree(hash->value);
return SSH_GSS_OK;
}
static void ssh_sspi_bind_fns(struct ssh_gss_library *lib)
{
lib->indicate_mech = ssh_sspi_indicate_mech;
lib->import_name = ssh_sspi_import_name;
lib->release_name = ssh_sspi_release_name;
lib->init_sec_context = ssh_sspi_init_sec_context;
lib->free_tok = ssh_sspi_free_tok;
lib->acquire_cred = ssh_sspi_acquire_cred;
lib->release_cred = ssh_sspi_release_cred;
lib->get_mic = ssh_sspi_get_mic;
lib->verify_mic = ssh_sspi_verify_mic;
lib->free_mic = ssh_sspi_free_mic;
lib->display_status = ssh_sspi_display_status;
}
#else
/* Dummy function so this source file defines something if NO_GSSAPI
is defined. */
void ssh_gss_init(void)
{
}
#endif
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