RE: [PATCH] fs/exec: require argv[0] presence in do_execveat_common()

From: David Laight <David.Laight@ACULAB.COM>
To: 'Kees Cook' <keescook@chromium.org>,
	Ariadne Conill <ariadne@dereferenced.org>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
	"Eric Biederman" <ebiederm@xmission.com>,
	Alexander Viro <viro@zeniv.linux.org.uk>
Subject: RE: [PATCH] fs/exec: require argv[0] presence in do_execveat_common()
Date: Wed, 26 Jan 2022 16:59:53 +0000	[thread overview]
Message-ID: <a33e8f5318e94e01ac4126bc4870b59a@AcuMS.aculab.com> (raw)
In-Reply-To: <39480927-B17F-4573-B335-7FCFD81AB997@chromium.org>

From: Kees Cook
> Sent: 26 January 2022 07:28
...
> >
> >There shouldn't be anything legitimate actually doing this in userspace.
> 
> I spoke too soon.
> 
> Unfortunately, this is not the case:
> https://codesearch.debian.net/search?q=execve%5C+*%5C%28%5B%5E%2C%5D%2B%2C+*NULL&literal=0
> 
> Lots of stuff likes to do:
> execve(path, NULL, NULL);
> 
> Do these things depend on argc==0 would be my next question...

What about ensuring that argv[0] and argv[1] are always present
and both NULL when argc is 0?

Then programs that just scan from argv[1] until they get a NULL
will always be fine.

	David

-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)