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

Al Viro viro at zeniv.linux.org.uk
Sat Sep 19 16:55:58 UTC 2020

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(;;) {

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