krb5 commit [krb5-1.17]: Fix gssalloc_realloc() on Windows

[Greg Hudson]

https://github.com/krb5/krb5/commit/c1f08b6ff1b3988da72e64093e9818f15c83619f
commit c1f08b6ff1b3988da72e64093e9818f15c83619f
Author: Greg Hudson <ghudson at mit.edu>
Date:   Mon Oct 21 10:29:35 2019 -0400

    Fix gssalloc_realloc() on Windows
    
    gss_inquire_sec_context_by_oid(GSS_C_INQ_SSPI_SESSION_KEY) fails on
    Windows because generic_gss_add_buffer_set_member() relies on the
    ability to realloc() a null pointer.  Unlike realloc(), HeapReAlloc()
    requires an input pointer that (from the MSDN documentation) "is
    returned by an earlier call to the HeapAlloc or HeapReAlloc function".
    So gssalloc_realloc() must test for null inputs and call HeapAlloc()
    instead.
    
    Reported by Eric Pauly.
    
    (cherry picked from commit d66b311093f1782c3610bbc77bd78fce411e8f79)
    
    ticket: 8735
    version_fixed: 1.17.1

 src/lib/gssapi/generic/gssapi_alloc.h |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)

diff --git a/src/lib/gssapi/generic/gssapi_alloc.h b/src/lib/gssapi/generic/gssapi_alloc.h
index 9a5cd98..fff88fd 100644
--- a/src/lib/gssapi/generic/gssapi_alloc.h
+++ b/src/lib/gssapi/generic/gssapi_alloc.h
@@ -36,6 +36,9 @@ gssalloc_calloc(size_t count, size_t size)
 static inline void *
 gssalloc_realloc(void *value, size_t size)
 {
+    /* Unlike realloc(), HeapReAlloc() does not work on null values. */
+    if (value == NULL)
+        return HeapAlloc(GetProcessHeap(), 0, size);
     return HeapReAlloc(GetProcessHeap(), 0, value, size);
 }