bpo-33706: Fix pymain_parse_cmdline_impl() (GH-7283)

vstinner · web-flow · commit 58d1683255ab · 2018-05-31T15:09:28.000+02:00
Fix a crash in Python initialization when parsing the command line
options.

Fix memcpy() size parameter: previously, we read one wchar_t after
the end of _PyOS_optarg. Moreover, don't copy the trailingg NUL
character: we write it manually anyway.

Thanks Christoph Gohlke for the bug report and the fix!
diff --git a/Misc/NEWS.d/next/Core and Builtins/2018-05-31-14-50-04.bpo-33706.ztlH04.rst b/Misc/NEWS.d/next/Core and Builtins/2018-05-31-14-50-04.bpo-33706.ztlH04.rst
@@ -0,0 +1,2 @@
+Fix a crash in Python initialization when parsing the command line options.
+Thanks Christoph Gohlke for the bug report and the fix!
diff --git a/Modules/main.c b/Modules/main.c
@@ -761,7 +761,7 @@ pymain_parse_cmdline_impl(_PyMain *pymain, _Py_CommandLineDetails *cmdline)
                 pymain->err = _Py_INIT_NO_MEMORY();
                 return -1;
             }
-            memcpy(command, _PyOS_optarg, len * sizeof(wchar_t));
+            memcpy(command, _PyOS_optarg, (len - 2) * sizeof(wchar_t));
             command[len - 2] = '\n';
             command[len - 1] = 0;
             pymain->command = command;

Original file line number	Diff line number	Diff line change
`@@ -0,0 +1,2 @@`
	`1`	`+Fix a crash in Python initialization when parsing the command line options.`
	`2`	`+Thanks Christoph Gohlke for the bug report and the fix!`
Original file line number	Diff line number	Diff line change
`@@ -761,7 +761,7 @@ pymain_parse_cmdline_impl(_PyMain pymain, _Py_CommandLineDetails cmdline)`
`761`	`761`	`pymain->err = _Py_INIT_NO_MEMORY();`
`762`	`762`	`return -1;`
`763`	`763`	`}`
`764`		`- memcpy(command, _PyOS_optarg, len * sizeof(wchar_t));`
	`764`	`+ memcpy(command, _PyOS_optarg, (len - 2) * sizeof(wchar_t));`
`765`	`765`	`command[len - 2] = '\n';`
`766`	`766`	`command[len - 1] = 0;`
`767`	`767`	`pymain->command = command;`