Re: [Linux-kernel-mentees] [PATCH] fs: fix KMSAN uninit-value bug by initializing nd in do_file_open_root

From: Al Viro
Date: Sat Sep 19 2020 - 12:56:14 EST

On Sat, Sep 19, 2020 at 05:17:27PM +0100, Al Viro wrote:

> Lovely... That would get an empty path and non-directory for a starting
> point, but it should end up with LAST_ROOT in nd->last_type. Which should
> not be able to reach the readers of those fields... Which kernel had
> that been on?

Yecchhh... I see what's going on; I suspect that this ought to be enough.
Folks, could somebody test it on the original reproducer setup?

diff --git a/fs/namei.c b/fs/namei.c
index e99e2a9da0f7..3f02cae7e73f 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -2113,8 +2113,10 @@ static int link_path_walk(const char *name, struct nameidata *nd)
return PTR_ERR(name);
while (*name=='/')
- if (!*name)
+ if (!*name) {
+ nd->dir_mode = 0; // short-circuit the 'hardening' idiocy
return 0;
+ }

/* At this point we know we have a real path component. */
for(;;) {