win32: let stat(2) report numeric uids for local users

Further extend file identification so stat(2) returns the relative
identifier as a numeric uid for files with owner SIDs that look like
a local or domain user.

See:

   https://blogs.technet.microsoft.com/markrussinovich/2009/11/03/the-machine-sid-duplication-myth-and-why-sysprep-matters/
   https://cygwin.com/cygwin-ug-net/ntsec.html

2 files changed, 49 insertions, 10 deletions

diff --git a/include/mingw.h b/include/mingw.h
index f8e833138..f99582ca5 100644
--- a/include/mingw.h
+++ b/include/mingw.h
@@ -8,8 +8,8 @@
 typedef int gid_t;
 typedef int uid_t;
 
-#define DEFAULT_UID 1000
-#define DEFAULT_GID 1000
+#define DEFAULT_UID 4095
+#define DEFAULT_GID 4095
 
 /*
  * arpa/inet.h
diff --git a/win32/mingw.c b/win32/mingw.c
index d7bdc10f6..f84cb76d3 100644
--- a/win32/mingw.c
+++ b/win32/mingw.c
@@ -391,13 +391,20 @@ static int has_exec_format(const char *name)
 }
 
 #if ENABLE_FEATURE_IDENTIFY_OWNER
-static int file_belongs_to_me(HANDLE fh)
+static uid_t file_owner(HANDLE fh)
 {
         PSID pSidOwner;
         PSECURITY_DESCRIPTOR pSD;
         static PTOKEN_USER user = NULL;
         static int initialised = 0;
         int equal;
+        uid_t uid = 0;
+        DWORD *ptr;
+        unsigned char prefix[] = {
+                        0x01, 0x05, 0x00, 0x00,
+                        0x00, 0x00, 0x00, 0x05,
+                        0x15, 0x00, 0x00, 0x00
+        };
 
         /*  get SID of current user */
         if (!initialised) {
@@ -418,16 +425,51 @@ static int file_belongs_to_me(HANDLE fh)
         }
 
         if (user == NULL)
-                return TRUE;
+                return DEFAULT_UID;
 
         /* get SID of file's owner */
         if (GetSecurityInfo(fh, SE_FILE_OBJECT, OWNER_SECURITY_INFORMATION,
                         &pSidOwner, NULL, NULL, NULL, &pSD) != ERROR_SUCCESS)
-                return FALSE;
+                return 0;
 
         equal = EqualSid(pSidOwner, user->User.Sid);
         LocalFree(pSD);
-        return equal;
+
+        if (equal)
+                return DEFAULT_UID;
+
+        /* for local or domain users use the RID as uid */
+        if (memcmp(pSidOwner, prefix, sizeof(prefix)) == 0) {
+                ptr = (DWORD *)pSidOwner;
+                if (ptr[6] >= 500 && ptr[6] < DEFAULT_UID)
+                        uid = (uid_t)ptr[6];
+        }
+        return uid;
+
+#if 0
+        /* this is how it would be done properly using the API */
+        {
+                PSID_IDENTIFIER_AUTHORITY auth;
+                unsigned char *count;
+                PDWORD subauth;
+                unsigned char nt_auth[] = {
+                                0x00, 0x00, 0x00, 0x00, 0x00, 0x05
+                };
+
+                if (IsValidSid(pSidOwner) ) {
+                        auth = GetSidIdentifierAuthority(pSidOwner);
+                        count = GetSidSubAuthorityCount(pSidOwner);
+                        subauth = GetSidSubAuthority(pSidOwner, 0);
+                        if (memcmp(auth, nt_auth, sizeof(nt_auth)) == 0 &&
+                                        *count == 5 && *subauth == 21) {
+                                subauth = GetSidSubAuthority(pSidOwner, 4);
+                                if (*subauth >= 500 && *subauth < DEFAULT_UID)
+                                        uid = (uid_t)*subauth;
+                        }
+                }
+                return uid;
+        }
+#endif
 }
 #endif
 
@@ -499,10 +541,7 @@ static int do_lstat(int follow, const char *file_name, struct mingw_stat *buf)
                                                         hdata.nNumberOfLinks;
                         }
 #if ENABLE_FEATURE_IDENTIFY_OWNER
-                        if (!file_belongs_to_me(fh)) {
-                                buf->st_uid = 0;
-                                buf->st_gid = 0;
-                        }
+                        buf->st_uid = buf->st_gid = file_owner(fh);
 #endif
                         CloseHandle(fh);
                 }