linux-kernel - Re: [PATCH] fs/pidfs: when time ns disabled add check for ioctl

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Message-ID: <20240722-graben-narren-76c25de0f0dd@brauner>
Date: Mon, 22 Jul 2024 10:00:58 +0200
From: Christian Brauner <brauner@...nel.org>
To: Edward Adam Davis <eadavis@...com>
Cc: syzbot+34a0ee986f61f15da35d@...kaller.appspotmail.com, jack@...e.cz, 
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org, syzkaller-bugs@...glegroups.com, 
	viro@...iv.linux.org.uk
Subject: Re: [PATCH] fs/pidfs: when time ns disabled add check for ioctl

On Sun, Jul 21, 2024 at 02:23:12PM GMT, Edward Adam Davis wrote:
> syzbot call pidfd_ioctl() with cmd "PIDFD_GET_TIME_NAMESPACE" and disabled
> CONFIG_TIME_NS, since time_ns is NULL, it will make NULL ponter deref in
> open_namespace.
> 
> Reported-and-tested-by: syzbot+34a0ee986f61f15da35d@...kaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=34a0ee986f61f15da35d
> Signed-off-by: Edward Adam Davis <eadavis@...com>
> ---

Hm, nsproxy is really messy in that regard. Some namespaces will always
be set to init_<type>_ns and others will be set to NULL.

That's an invitation for bugs such as this. Imho the correct fix is to
change nsproxy to always set nsp-><type>_ns to init_<type>_ns and no
code ever needs to worry about dereferencing NULL.

But that'll require more changes so this seems an appropriate fix for now.