Fix miscalculation of itemsafter in array_set_slice().

If the slice to be assigned to was before the existing array lower bound
(requiring at least one null element to spring into existence to fill the
gap), the code miscalculated how many entries needed to be copied from
the old array's null bitmap.  This could result in trashing the array's
data area (as seen in bug #5840 from Karsten Loesing), or worse.

This has been broken since we first allowed the behavior of assigning to
non-adjacent slices, in 8.2.  Back-patch to all affected versions.

diff --git a/src/backend/utils/adt/arrayfuncs.c b/src/backend/utils/adt/arrayfuncs.c
index 4e33bbe2ca9adc150116e08213a2f9c4b3e0666f..f06c4e565710db06ba803d8734c9f7f52ba2a400 100644 (file)
--- a/src/backend/utils/adt/arrayfuncs.c
+++ b/src/backend/utils/adt/arrayfuncs.c
@@ -2459,6 +2459,7 @@ array_set_slice(ArrayType *array,
        {
                /*
                 * here we must allow for possibility of slice larger than orig array
+                * and/or not adjacent to orig array subscripts
                 */
                int                     oldlb = ARR_LBOUND(array)[0];
                int                     oldub = oldlb + ARR_DIMS(array)[0] - 1;
@@ -2467,10 +2468,12 @@ array_set_slice(ArrayType *array,
                char       *oldarraydata = ARR_DATA_PTR(array);
                bits8      *oldarraybitmap = ARR_NULLBITMAP(array);
 
+               /* count/size of old array entries that will go before the slice */
                itemsbefore = Min(slicelb, oldub + 1) - oldlb;
                lenbefore = array_nelems_size(oldarraydata, 0, oldarraybitmap,
                                                                          itemsbefore,
                                                                          elmlen, elmbyval, elmalign);
+               /* count/size of old array entries that will be replaced by slice */
                if (slicelb > sliceub)
                {
                        nolditems = 0;
@@ -2484,7 +2487,8 @@ array_set_slice(ArrayType *array,
                                                                                        nolditems,
                                                                                        elmlen, elmbyval, elmalign);
                }
-               itemsafter = oldub - sliceub;
+               /* count/size of old array entries that will go after the slice */
+               itemsafter = oldub + 1 - Max(sliceub + 1, oldlb);
                lenafter = olddatasize - lenbefore - olditemsize;
        }