linux-kernel - Re: [PATCH] KEYS: fix dereferencing NULL payload with nonzero length

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Mon, 3 Apr 2017 14:30:41 -0700
From:   Eric Biggers <ebiggers3@...il.com>
To:     David Howells <dhowells@...hat.com>
Cc:     keyrings@...r.kernel.org, linux-security-module@...r.kernel.org,
        linux-kernel@...r.kernel.org, Eric Biggers <ebiggers@...gle.com>,
        stable@...r.kernel.org
Subject: Re: [PATCH] KEYS: fix dereferencing NULL payload with nonzero length

On Mon, Apr 03, 2017 at 08:20:44PM +0100, David Howells wrote:
> Eric Biggers <ebiggers3@...il.com> wrote:
> 
> > > > -	if (_payload) {
> > > > +	if (plen) {
> > > 
> > > "if (_payload && plen)" would be better.
> > > 
> > > David
> > 
> > No, that doesn't solve the problem.  The problem is that userspace can pass
> > in a NULL payload with nonzero length, causing the kernel to dereference a
> > NULL pointer for some key types.  For example:
> 
> Okay, in that case, I think there should be an else-statement that clears plen
> if !_payload.
> 
> David

I think it's preferable to return EFAULT in the case in question.  Most syscalls
work like that, i.e. if you say you have 100 bytes (or any number > 0) at
address NULL you'll get EFAULT.

Also note that anyone doing this before would have been either crashing the
kernel or getting EINVAL.  So starting to return EFAULT would be very unlikely
to break anything.

- Eric