Fix array- and path-creating functions to ensure padding bytes are zeroes.

Per recent discussion, it's important for all computed datums (not only the
results of input functions) to not contain any ill-defined (uninitialized)
bits.  Failing to ensure that can result in equal() reporting that
semantically indistinguishable Consts are not equal, which in turn leads to
bizarre and undesirable planner behavior, such as in a recent example from
David Johnston.  We might eventually try to fix this in a general manner by
allowing datatypes to define identity-testing functions, but for now the
path of least resistance is to expect datatypes to force all unused bits
into consistent states.

Per some testing by Noah Misch, array and path functions seem to be the
only ones presenting risks at the moment, so I looked through all the
functions in adt/array*.c and geo_ops.c and fixed them as necessary.  In
the array functions, the easiest/safest fix is to allocate result arrays
with palloc0 instead of palloc.  Possibly in future someone will want to
look into whether we can just zero the padding bytes, but that looks too
complex for a back-patchable fix.  In the path functions, we already had a
precedent in path_in for just zeroing the one known pad field, so duplicate
that code as needed.

Back-patch to all supported branches.

diff --git a/src/backend/utils/adt/array_userfuncs.c b/src/backend/utils/adt/array_userfuncs.c
index 67222b199411f27c1b5591e12c0cb6c262478a6a..62ff6f49f33a7332a357753382997e54259337e8 100644 (file)
--- a/src/backend/utils/adt/array_userfuncs.c
+++ b/src/backend/utils/adt/array_userfuncs.c
@@ -376,7 +376,7 @@ array_cat(PG_FUNCTION_ARGS)
        dataoffset = 0;         /* marker for no null bitmap */
        nbytes = ndatabytes + ARR_OVERHEAD_NONULLS(ndims);
    }
-   result = (ArrayType *) palloc(nbytes);
+   result = (ArrayType *) palloc0(nbytes);
    SET_VARSIZE(result, nbytes);
    result->ndim = ndims;
    result->dataoffset = dataoffset;

diff --git a/src/backend/utils/adt/arrayfuncs.c b/src/backend/utils/adt/arrayfuncs.c
index b36af2c0f09b55646db3da61671737edf8b7f101..87e611573abdf5a9f649e43e8ce6ab5cbc93a1b6 100644 (file)
--- a/src/backend/utils/adt/arrayfuncs.c
+++ b/src/backend/utils/adt/arrayfuncs.c
@@ -1273,7 +1273,7 @@ array_recv(PG_FUNCTION_ARGS)
        dataoffset = 0;         /* marker for no null bitmap */
        nbytes += ARR_OVERHEAD_NONULLS(ndim);
    }
-   retval = (ArrayType *) palloc(nbytes);
+   retval = (ArrayType *) palloc0(nbytes);
    SET_VARSIZE(retval, nbytes);
    retval->ndim = ndim;
    retval->dataoffset = dataoffset;
@@ -1911,7 +1911,7 @@ array_get_slice(ArrayType *array,
        bytes += ARR_OVERHEAD_NONULLS(ndim);
    }
 
-   newarray = (ArrayType *) palloc(bytes);
+   newarray = (ArrayType *) palloc0(bytes);
    SET_VARSIZE(newarray, bytes);
    newarray->ndim = ndim;
    newarray->dataoffset = dataoffset;
@@ -2164,7 +2164,7 @@ array_set(ArrayType *array,
    /*
     * OK, create the new array and fill in header/dimensions
     */
-   newarray = (ArrayType *) palloc(newsize);
+   newarray = (ArrayType *) palloc0(newsize);
    SET_VARSIZE(newarray, newsize);
    newarray->ndim = ndim;
    newarray->dataoffset = newhasnulls ? overheadlen : 0;
@@ -2494,7 +2494,7 @@ array_set_slice(ArrayType *array,
 
    newsize = overheadlen + olddatasize - olditemsize + newitemsize;
 
-   newarray = (ArrayType *) palloc(newsize);
+   newarray = (ArrayType *) palloc0(newsize);
    SET_VARSIZE(newarray, newsize);
    newarray->ndim = ndim;
    newarray->dataoffset = newhasnulls ? overheadlen : 0;
@@ -2753,7 +2753,7 @@ array_map(FunctionCallInfo fcinfo, Oid inpType, Oid retType,
        dataoffset = 0;         /* marker for no null bitmap */
        nbytes += ARR_OVERHEAD_NONULLS(ndim);
    }
-   result = (ArrayType *) palloc(nbytes);
+   result = (ArrayType *) palloc0(nbytes);
    SET_VARSIZE(result, nbytes);
    result->ndim = ndim;
    result->dataoffset = dataoffset;
@@ -2889,7 +2889,7 @@ construct_md_array(Datum *elems,
        dataoffset = 0;         /* marker for no null bitmap */
        nbytes += ARR_OVERHEAD_NONULLS(ndims);
    }
-   result = (ArrayType *) palloc(nbytes);
+   result = (ArrayType *) palloc0(nbytes);
    SET_VARSIZE(result, nbytes);
    result->ndim = ndims;
    result->dataoffset = dataoffset;
@@ -2913,7 +2913,7 @@ construct_empty_array(Oid elmtype)
 {
    ArrayType  *result;
 
-   result = (ArrayType *) palloc(sizeof(ArrayType));
+   result = (ArrayType *) palloc0(sizeof(ArrayType));
    SET_VARSIZE(result, sizeof(ArrayType));
    result->ndim = 0;
    result->dataoffset = 0;

diff --git a/src/backend/utils/adt/geo_ops.c b/src/backend/utils/adt/geo_ops.c
index 10fc79f1162ca066dd6e6595273a8a95487b239f..c1276b78c12d57c4076e631a3acbc13261e0ff6a 100644 (file)
--- a/src/backend/utils/adt/geo_ops.c
+++ b/src/backend/utils/adt/geo_ops.c
@@ -1476,6 +1476,8 @@ path_recv(PG_FUNCTION_ARGS)
    SET_VARSIZE(path, size);
    path->npts = npts;
    path->closed = (closed ? 1 : 0);
+   /* prevent instability in unused pad bytes */
+   path->dummy = 0;
 
    for (i = 0; i < npts; i++)
    {
@@ -4090,6 +4092,8 @@ path_add(PG_FUNCTION_ARGS)
    SET_VARSIZE(result, size);
    result->npts = (p1->npts + p2->npts);
    result->closed = p1->closed;
+   /* prevent instability in unused pad bytes */
+   result->dummy = 0;
 
    for (i = 0; i < p1->npts; i++)
    {
@@ -4323,6 +4327,8 @@ poly_path(PG_FUNCTION_ARGS)
    SET_VARSIZE(path, size);
    path->npts = poly->npts;
    path->closed = TRUE;
+   /* prevent instability in unused pad bytes */
+   path->dummy = 0;
 
    for (i = 0; i < poly->npts; i++)
    {