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

From	Eric Biggers <ebiggers3@gmail.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH] KEYS: fix dereferencing NULL payload with nonzero length
Date	2017-04-03 23:40 +0200
Message-ID	<tshRE-3X5-29@gated-at.bofh.it> (permalink)
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On Mon, Apr 03, 2017 at 08:20:44PM +0100, David Howells wrote:
> Eric Biggers <ebiggers3@gmail.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

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[PATCH] KEYS: fix dereferencing NULL payload with nonzero length Eric Biggers <ebiggers3@gmail.com> - 2017-04-01 23:40 +0200
  Re: [PATCH] KEYS: fix dereferencing NULL payload with nonzero length David Howells <dhowells@redhat.com> - 2017-04-03 17:50 +0200
    Re: [PATCH] KEYS: fix dereferencing NULL payload with nonzero length Eric Biggers <ebiggers3@gmail.com> - 2017-04-03 20:00 +0200
      Re: [PATCH] KEYS: fix dereferencing NULL payload with nonzero length David Howells <dhowells@redhat.com> - 2017-04-03 21:30 +0200
        Re: [PATCH] KEYS: fix dereferencing NULL payload with nonzero length Eric Biggers <ebiggers3@gmail.com> - 2017-04-03 23:40 +0200

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