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 499d3578b31c0ad6d8d3c4c72640b60a383d89f2..274e867fdd169b7c6b48e6189c0945004df959b6 100644 (file)
--- a/src/backend/utils/adt/array_userfuncs.c
+++ b/src/backend/utils/adt/array_userfuncs.c
@@ -375,7 +375,7 @@ 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 a234f35eb8f561650add8cfd3fa4a44a36c550f7..f5218111db145d725e687d861829394de032b658 100644 (file)
--- a/src/backend/utils/adt/arrayfuncs.c
+++ b/src/backend/utils/adt/arrayfuncs.c
@@ -1339,7 +1339,7 @@ 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;
@@ -1977,7 +1977,7 @@ 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;
@@ -2230,7 +2230,7 @@ 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;
@@ -2560,7 +2560,7 @@ 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;
@@ -2819,7 +2819,7 @@ 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;
@@ -2955,7 +2955,7 @@ 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;
@@ -2979,7 +2979,7 @@ 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 b8cf9a8d0651b381235ef7f18c4fcd6ee81746ec..2cf2f6441173d2972879da83b3fa93fab978a22a 100644 (file)
--- a/src/backend/utils/adt/geo_ops.c
+++ b/src/backend/utils/adt/geo_ops.c
@@ -1478,6 +1478,8 @@ 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++)
    {
@@ -4253,6 +4255,8 @@ 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++)
    {
@@ -4486,6 +4490,8 @@ 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++)
    {