Teach contain_leaked_vars that assignment SubscriptingRefs are leaky.

array_get_element and array_get_slice qualify as leakproof, since
they will silently return NULL for bogus subscripts.  But
array_set_element and array_set_slice throw errors for such cases,
making them clearly not leakproof.  contain_leaked_vars was evidently
written with only the former case in mind, as it gave the wrong answer
for assignment SubscriptingRefs (nee ArrayRefs).

This would be a live security bug, were it not that assignment
SubscriptingRefs can only occur in INSERT and UPDATE target lists,
while we only care about leakproofness for qual expressions; so the
wrong answer can't occur in practice.  Still, that's a rather shaky
answer for a security-related question; and maybe in future somebody
will want to ask about leakproofness of a tlist.  So it seems wise to
fix and even back-patch this correction.

(We would need some change here anyway for the upcoming
generic-subscripting patch, since extensions might make different
tradeoffs about whether to throw errors.  Commit 558d77f20 attempted
to lay groundwork for that by asking check_functions_in_node whether a
SubscriptingRef contains leaky functions; but that idea fails now that
the implementation methods of a SubscriptingRef are not SQL-visible
functions that could be marked leakproof or not.)

Back-patch to 9.6.  While 9.5 has the same issue, the code's a bit
different.  It seems quite unlikely that we'd introduce any actual bug
in the short time 9.5 has left to live, so the work/risk/reward balance
isn't attractive for changing 9.5.

Discussion: https://postgr.es/m/3143742.1607368115@sss.pgh.pa.us
This commit is contained in:
Tom Lane 2020-12-08 17:50:54 -05:00
parent 5303706b32
commit 1f229f4fdc
1 changed files with 17 additions and 1 deletions

View File

@ -1602,7 +1602,6 @@ contain_leaked_vars_walker(Node *node, void *context)
case T_Var:
case T_Const:
case T_Param:
case T_ArrayRef:
case T_ArrayExpr:
case T_FieldSelect:
case T_FieldStore:
@ -1643,6 +1642,23 @@ contain_leaked_vars_walker(Node *node, void *context)
return true;
break;
case T_ArrayRef:
{
ArrayRef *aref = (ArrayRef *) node;
/*
* array assignment is leaky, but subscripted fetches
* are not
*/
if (aref->refassgnexpr != NULL)
{
/* Node is leaky, so reject if it contains Vars */
if (contain_var_clause(node))
return true;
}
}
break;
case T_RowCompareExpr:
{
/*