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 bca0b894422a8d731daa1df34f835a35a1edccd7..159353598fa63992589bce2d2391497d325f2681 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 df7190dbfc88ba8bd5144d1f81f7423b71439a8b..add2a55e5de9cf05e62aaf025682531d91c601c1 100644 (file)
--- a/src/backend/utils/adt/arrayfuncs.c
+++ b/src/backend/utils/adt/arrayfuncs.c
@@ -1314,7 +1314,7 @@ 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;
@@ -1952,7 +1952,7 @@ 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;
@@ -2205,7 +2205,7 @@ 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;
@@ -2535,7 +2535,7 @@ 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;
@@ -2794,7 +2794,7 @@ 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;
@@ -2930,7 +2930,7 @@ 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;
@@ -2954,7 +2954,7 @@ 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 3e93bac282f068341058987dd9995cdb76dc7fb3..9fe9cef2042d6f9f3dbfa551a549d6bb52e0b25c 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++)
        {