Fix Windows-only postmaster code to reject a connection request and continue,

rather than elog(FATAL), when there is no more room in ShmemBackendArray.
This is a security issue since too many connection requests arriving close
together could cause the postmaster to shut down, resulting in denial of
service.  Reported by Yoshiyuki Asaba, fixed by Magnus Hagander.

diff --git a/src/backend/postmaster/postmaster.c b/src/backend/postmaster/postmaster.c
index 31d370ebbb2efda7192e2ed4e604ce47606612b5..43deb57aa2c2ca1e744e7f73e2d47ea6415156eb 100644 (file)
--- a/src/backend/postmaster/postmaster.c
+++ b/src/backend/postmaster/postmaster.c
@@ -37,7 +37,7 @@
  *
  *
  * IDENTIFICATION
- *       $PostgreSQL: pgsql/src/backend/postmaster/postmaster.c,v 1.478 2006/01/05 10:07:45 petere Exp $
+ *       $PostgreSQL: pgsql/src/backend/postmaster/postmaster.c,v 1.479 2006/01/06 02:58:25 tgl Exp $
  *
  * NOTES
  *
@@ -147,7 +147,11 @@ typedef struct bkend
 static Dllist *BackendList;
 
 #ifdef EXEC_BACKEND
-#define NUM_BACKENDARRAY_ELEMS (2*MaxBackends)
+/* 
+ * Number of entries in the backend table. Twice the number of backends,
+ * plus four other subprocesses (stats, bgwriter, autovac, logger). 
+ */
+#define NUM_BACKENDARRAY_ELEMS (2*MaxBackends + 4)
 static Backend *ShmemBackendArray;
 #endif
 
@@ -3083,6 +3087,15 @@ internal_forkexec(int argc, char *argv[], Port *port)
        Assert(strncmp(argv[1], "-fork", 5) == 0);
        Assert(argv[2] == NULL);
 
+       /* Verify that there is room in the child list */
+       if (win32_numChildren >= NUM_BACKENDARRAY_ELEMS)
+       {
+               elog(LOG, "no room for child entry in backend list");
+               /* Report same error as for a fork failure on Unix */
+               errno = EAGAIN;
+               return -1;
+       }
+
        /* Set up shared memory for parameter passing */
        ZeroMemory(&sa, sizeof(sa));
        sa.nLength = sizeof(sa);