Make bit/varbit substring() treat any negative length as meaning "all the rest

of the string".  The previous coding treated only -1 that way, and would
produce an invalid result value for other negative values.

We ought to fix it so that 2-parameter bit substring() is a different C
function and the 3-parameter form throws error for negative length, but
that takes a pg_proc change which is impractical in the back branches;
and in any case somebody might be relying on -1 working this way.
So just do this as a back-patchable fix.

diff --git a/src/backend/utils/adt/varbit.c b/src/backend/utils/adt/varbit.c
index 6882231e617fb74ecdfa3b380f92e8619600a719..d98a8a613eefd6d127ceb0e07ae2799786890903 100644 (file)
--- a/src/backend/utils/adt/varbit.c
+++ b/src/backend/utils/adt/varbit.c
@@ -9,7 +9,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *       $PostgreSQL: pgsql/src/backend/utils/adt/varbit.c,v 1.61 2010/01/07 04:53:34 tgl Exp $
+ *       $PostgreSQL: pgsql/src/backend/utils/adt/varbit.c,v 1.62 2010/01/07 19:53:11 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -945,13 +945,23 @@ bitsubstr(PG_FUNCTION_ARGS)
                           *ps;
 
        bitlen = VARBITLEN(arg);
-       /* If we do not have an upper bound, set bitlen */
-       if (l == -1)
-               l = bitlen;
-       e = s + l;
        s1 = Max(s, 1);
-       e1 = Min(e, bitlen + 1);
-       if (s1 > bitlen || e1 < 1)
+       /* If we do not have an upper bound, use end of string */
+       if (l < 0)
+       {
+               e1 = bitlen + 1;
+       }
+       else
+       {
+               e = s + l;
+               /* guard against overflow, even though we don't allow L<0 here */
+               if (e < s)
+                       ereport(ERROR,
+                                       (errcode(ERRCODE_SUBSTRING_ERROR),
+                                        errmsg("negative substring length not allowed")));
+               e1 = Min(e, bitlen + 1);
+       }
+       if (s1 > bitlen || e1 <= s1)
        {
                /* Need to return a zero-length bitstring */
                len = VARBITTOTALLEN(0);