krb5: fix `output_token` allocators in the GSS debug stub (Windows)

Before this patch system `malloc()`/`free()` were used to allocate
the buffer returned in the `output_token` object from the debug stub
of `gss_init_sec_context()` when enabled via `CURL_STUB_GSS_CREDS` in
debug-enabled libcurl builds. This object is later released via stock
`gss_release_buffer()`, which, in the Windows builds of MIT Kerberos,
doesn't use the system `free()`, but the Win32 `HeapFree()`.

Fix it by using the GSS alloc/free macros: `gssalloc_malloc()` and
`gssalloc_free()` from `gssapi_alloc.h`.

To make this work without MIT Kerberos feature detection, use a canary
macro to detect a version which installs `gssapi_alloc.h` for Windows.
For <1.15 (2016-11-30) releases, that do not install it, disable the GSS
debug stub in libcurl.

Strictly speaking, non-Windows builds would also need to use GSS
allocators, but, detecting support for `gssapi_alloc.h` is impossible
without build-level logic. Built-level logic is complex and overkill,
and MIT Kerberos, as of 1.22.1, uses standard malloc/free on
non-Windows platforms anyway. (except in GSS debug builds.)

Follow-up to 73840836a51c443e6b5d385014ce1c8f5be3e02b #17752

Closes #19064

diff --git a/lib/curl_gssapi.c b/lib/curl_gssapi.c
index 42ccaa3e2962ea8e1035cf45ff08666b31c94093..74128559c17268168b8591664fbbb84359b36510 100644 (file)
--- a/lib/curl_gssapi.c
+++ b/lib/curl_gssapi.c
@@ -29,6 +29,28 @@
 #include "curl_gssapi.h"
 #include "sendf.h"
 
+#ifdef DEBUGBUILD
+#if defined(HAVE_GSSGNU) || !defined(_WIN32)
+/* To avoid memdebug macro replacement, wrap the name in parentheses to call
+   the original version. It is freed via the GSS API gss_release_buffer(). */
+#define Curl_gss_alloc (malloc)
+#define Curl_gss_free  (free)
+#define CURL_GSS_STUB
+/* For correctness this would be required for all platforms, not only Windows,
+   but, as of v1.22.1, MIT Kerberos uses a special allocator only for Windows,
+   and the availability of 'gssapi/gssapi_alloc.h' is difficult to detect,
+   because GSS headers are not versioned, and there is also no other macro to
+   indicate 1.18+ vs. previous versions. On Windows we can use 'GSS_S_BAD_MIC'.
+ */
+#elif defined(_WIN32) && defined(GSS_S_BAD_MIC) /* MIT Kerberos 1.15+ */
+/* MIT Kerberos 1.10+ (Windows), 1.18+ (all platforms), missing from GNU GSS */
+#include <gssapi/gssapi_alloc.h>
+#define Curl_gss_alloc gssalloc_malloc
+#define Curl_gss_free  gssalloc_free
+#define CURL_GSS_STUB
+#endif
+#endif /* DEBUGBUILD */
+
 /* The last 2 #include files should be in this order */
 #include "curl_memory.h"
 #include "memdebug.h"
@@ -51,7 +73,7 @@ gss_OID_desc Curl_krb5_mech_oid CURL_ALIGN8 = {
   9, CURL_UNCONST("\x2a\x86\x48\x86\xf7\x12\x01\x02\x02")
 };
 
-#ifdef DEBUGBUILD
+#ifdef CURL_GSS_STUB
 enum min_err_code {
   STUB_GSS_OK = 0,
   STUB_GSS_NO_MEMORY,
@@ -212,9 +234,7 @@ stub_gss_init_sec_context(OM_uint32 *min,
     ctx->flags = req_flags;
   }
 
-  /* To avoid memdebug macro replacement, wrap the name in parentheses to call
-     the original version. It is freed via the GSS API gss_release_buffer(). */
-  token = (malloc)(length);
+  token = Curl_gss_alloc(length);
   if(!token) {
     free(ctx);
     *min = STUB_GSS_NO_MEMORY;
@@ -229,14 +249,14 @@ stub_gss_init_sec_context(OM_uint32 *min,
     major_status = gss_display_name(&minor_status, target_name,
                                     &target_desc, &name_type);
     if(GSS_ERROR(major_status)) {
-      (free)(token);
+      Curl_gss_free(token);
       free(ctx);
       *min = STUB_GSS_NO_MEMORY;
       return GSS_S_FAILURE;
     }
 
     if(strlen(creds) + target_desc.length + 5 >= sizeof(ctx->creds)) {
-      (free)(token);
+      Curl_gss_free(token);
       free(ctx);
       *min = STUB_GSS_NO_MEMORY;
       return GSS_S_FAILURE;
@@ -252,7 +272,7 @@ stub_gss_init_sec_context(OM_uint32 *min,
   }
 
   if(used >= length) {
-    (free)(token);
+    Curl_gss_free(token);
     free(ctx);
     *min = STUB_GSS_NO_MEMORY;
     return GSS_S_FAILURE;
@@ -294,7 +314,7 @@ stub_gss_delete_sec_context(OM_uint32 *min,
 
   return GSS_S_COMPLETE;
 }
-#endif /* DEBUGBUILD */
+#endif /* CURL_GSS_STUB */
 
 OM_uint32 Curl_gss_init_sec_context(struct Curl_easy *data,
                                     OM_uint32 *minor_status,
@@ -324,7 +344,7 @@ OM_uint32 Curl_gss_init_sec_context(struct Curl_easy *data,
   if(data->set.gssapi_delegation & CURLGSSAPI_DELEGATION_FLAG)
     req_flags |= GSS_C_DELEG_FLAG;
 
-#ifdef DEBUGBUILD
+#ifdef CURL_GSS_STUB
   if(getenv("CURL_STUB_GSS_CREDS"))
     return stub_gss_init_sec_context(minor_status,
                                      GSS_C_NO_CREDENTIAL, /* cred_handle */
@@ -339,7 +359,7 @@ OM_uint32 Curl_gss_init_sec_context(struct Curl_easy *data,
                                      output_token,
                                      ret_flags,
                                      NULL /* time_rec */);
-#endif /* DEBUGBUILD */
+#endif /* CURL_GSS_STUB */
 
   return gss_init_sec_context(minor_status,
                               GSS_C_NO_CREDENTIAL, /* cred_handle */
@@ -360,12 +380,12 @@ OM_uint32 Curl_gss_delete_sec_context(OM_uint32 *min,
                                       gss_ctx_id_t *context,
                                       gss_buffer_t output_token)
 {
-#ifdef DEBUGBUILD
+#ifdef CURL_GSS_STUB
   if(getenv("CURL_STUB_GSS_CREDS"))
     return stub_gss_delete_sec_context(min,
                                      (struct stub_gss_ctx_id_t_desc **)context,
                                      output_token);
-#endif /* DEBUGBUILD */
+#endif /* CURL_GSS_STUB */
 
   return gss_delete_sec_context(min, context, output_token);
 }