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bpo-37947: Avoid double-decrement in symtable recursion counting #15593

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Merged
merged 3 commits into from
Aug 29, 2019
Merged

bpo-37947: Avoid double-decrement in symtable recursion counting #15593

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eb863e1
bpo-37947: Avoid double-decrement in symtable recursion counting
ncoghlan Aug 29, 2019
b4a341e
Ensure the symtable recursion accounting balances
ncoghlan Aug 29, 2019
6e83dc2
Remove spurious line
ncoghlan Aug 29, 2019
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18 changes: 14 additions & 4 deletions Python/symtable.c
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Original file line number Diff line number Diff line change
Expand Up @@ -266,6 +266,7 @@ PySymtable_BuildObject(mod_ty mod, PyObject *filename, PyFutureFeatures *future)
int i;
PyThreadState *tstate;
int recursion_limit = Py_GetRecursionLimit();
int starting_recursion_depth;

if (st == NULL)
return NULL;
Expand All @@ -284,8 +285,9 @@ PySymtable_BuildObject(mod_ty mod, PyObject *filename, PyFutureFeatures *future)
return NULL;
}
/* Be careful here to prevent overflow. */
st->recursion_depth = (tstate->recursion_depth < INT_MAX / COMPILER_STACK_FRAME_SCALE) ?
starting_recursion_depth = (tstate->recursion_depth < INT_MAX / COMPILER_STACK_FRAME_SCALE) ?
tstate->recursion_depth * COMPILER_STACK_FRAME_SCALE : tstate->recursion_depth;
st->recursion_depth = starting_recursion_depth;
st->recursion_limit = (recursion_limit < INT_MAX / COMPILER_STACK_FRAME_SCALE) ?
recursion_limit * COMPILER_STACK_FRAME_SCALE : recursion_limit;

Expand Down Expand Up @@ -329,6 +331,14 @@ PySymtable_BuildObject(mod_ty mod, PyObject *filename, PyFutureFeatures *future)
PySymtable_Free(st);
return NULL;
}
/* Check that the recursion depth counting balanced correctly */
if (st->recursion_depth != starting_recursion_depth) {
PyErr_Format(PyExc_SystemError,
"symtable analysis recursion depth mismatch (before=%d, after=%d)",
starting_recursion_depth, st->recursion_depth);
PySymtable_Free(st);
return NULL;
}
/* Make the second symbol analysis pass */
if (symtable_analyze(st))
return st;
Expand Down Expand Up @@ -1501,16 +1511,16 @@ symtable_handle_namedexpr(struct symtable *st, expr_ty e)
PyErr_SyntaxLocationObject(st->st_filename,
e->lineno,
e->col_offset);
VISIT_QUIT(st, 0);
return 0;
}
if (st->st_cur->ste_comprehension) {
/* Inside a comprehension body, so find the right target scope */
if (!symtable_extend_namedexpr_scope(st, e->v.NamedExpr.target))
VISIT_QUIT(st, 0);
return 0;
}
VISIT(st, expr, e->v.NamedExpr.value);
VISIT(st, expr, e->v.NamedExpr.target);
VISIT_QUIT(st, 1);
return 1;
}

static int
Expand Down