closes bpo-39510: Fix use-after-free in BufferedReader.readinto() (GH-18295)
When called on a closed object, readinto() segfaults on account
of a write to a freed buffer:
==220553== Process terminating with default action of signal 11 (SIGSEGV): dumping core
==220553== Access not within mapped region at address 0x2A
==220553== at 0x48408A0: memmove (vg_replace_strmem.c:1272)
==220553== by 0x58DB0C: _buffered_readinto_generic (bufferedio.c:972)
==220553== by 0x58DCBA: _io__Buffered_readinto_impl (bufferedio.c:1053)
==220553== by 0x58DCBA: _io__Buffered_readinto (bufferedio.c.h:253)
Reproducer:
reader = open ("/dev/zero", "rb")
_void = reader.read (42)
reader.close ()
reader.readinto (bytearray (42)) ### BANG!
The problem exists since 2012 when commit dc469454ec added code
to free the read buffer on close().
Signed-off-by: Philipp Gesang <philipp.gesang@intra2net.com>
diff --git a/Modules/_io/bufferedio.c b/Modules/_io/bufferedio.c
index 586e93f..ddd17a2 100644
--- a/Modules/_io/bufferedio.c
+++ b/Modules/_io/bufferedio.c
@@ -965,6 +965,7 @@
PyObject *res = NULL;
CHECK_INITIALIZED(self)
+ CHECK_CLOSED(self, "readinto of closed file")
n = Py_SAFE_DOWNCAST(READAHEAD(self), Py_off_t, Py_ssize_t);
if (n > 0) {