pythongh-131505: Move len boundary assertions before using len. (pythonGH-131536)

naya451 · miss-islington · commit 3ef70360bb0a · 2025-05-19T15:10:47.000Z
Move len boundary assertions before using len. (cherry picked from commit c45e661) Co-authored-by: naya451 <41294408+naya451@users.noreply.github.com>
diff --git a/Modules/_io/bytesio.c b/Modules/_io/bytesio.c
@@ -583,9 +583,9 @@ _io_BytesIO_readinto_impl(bytesio *self, Py_buffer *buffer)
             len = 0;
     }
 
-    memcpy(buffer->buf, PyBytes_AS_STRING(self->buf) + self->pos, len);
     assert(self->pos + len < PY_SSIZE_T_MAX);
     assert(len >= 0);
+    memcpy(buffer->buf, PyBytes_AS_STRING(self->buf) + self->pos, len);
     self->pos += len;
 
     return PyLong_FromSsize_t(len);

Original file line number	Diff line number	Diff line change
`@@ -583,9 +583,9 @@ _io_BytesIO_readinto_impl(bytesio self, Py_buffer buffer)`
`583`	`583`	`len = 0;`
`584`	`584`	`}`
`585`	`585`
`586`		`- memcpy(buffer->buf, PyBytes_AS_STRING(self->buf) + self->pos, len);`
`587`	`586`	`assert(self->pos + len < PY_SSIZE_T_MAX);`
`588`	`587`	`assert(len >= 0);`
	`588`	`+ memcpy(buffer->buf, PyBytes_AS_STRING(self->buf) + self->pos, len);`
`589`	`589`	`self->pos += len;`
`590`	`590`
`591`	`591`	`return PyLong_FromSsize_t(len);`