Issue #12973: Fix itertools bug caused by signed integer overflow. Thanks Stefan Krah.
diff --git a/Misc/NEWS b/Misc/NEWS
index fd98d02..1b03736 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -17,9 +17,9 @@
- Issue #13021: Missing decref on an error path. Thanks to Suman Saha for
finding the bug and providing a patch.
-- Issue #12973: Fix overflow check that relied on undefined behaviour in
- list_repeat. This bug caused test_list to fail with recent versions
- of Clang.
+- Issue #12973: Fix overflow checks that relied on undefined behaviour in
+ list_repeat (listobject.c) and islice_next (itertoolsmodule.c). These bugs
+ caused test failures with recent versions of Clang.
- Issue #12802: the Windows error ERROR_DIRECTORY (numbered 267) is now
mapped to POSIX errno ENOTDIR (previously EINVAL).
diff --git a/Modules/itertoolsmodule.c b/Modules/itertoolsmodule.c
index 71d5bb6..8b6fa85 100644
--- a/Modules/itertoolsmodule.c
+++ b/Modules/itertoolsmodule.c
@@ -1234,7 +1234,9 @@
return NULL;
lz->cnt++;
oldnext = lz->next;
- lz->next += lz->step;
+ /* The (size_t) cast below avoids the danger of undefined
+ behaviour from signed integer overflow. */
+ lz->next += (size_t)lz->step;
if (lz->next < oldnext || (stop != -1 && lz->next > stop))
lz->next = stop;
return item;