linux-kernel - Re: [PATCH] crypto_user: Fix out-of-bounds read

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Date:	Wed, 23 Apr 2014 08:48:34 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Dan Carpenter <dan.carpenter@...cle.com>
Cc:	linux-crypto@...r.kernel.org,
	"security@...nel.org" <security@...nel.org>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	"David S. Miller" <davem@...emloft.net>, stable@...r.kernel.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] crypto_user: Fix out-of-bounds read

On Apr 23, 2014 4:40 AM, "Dan Carpenter" <dan.carpenter@...cle.com> wrote:
>
> On Tue, Apr 22, 2014 at 12:30:28PM -0700, Andy Lutomirski wrote:
> > This is unlikely to be exploitable for anything except an OOPS.
> >
> > Cc: stable@...r.kernel.org
> > Signed-off-by: Andy Lutomirski <luto@...capital.net>
> > ---
> >
> > Notes:
> >     This is entirely untested, but it looks obviously correct to me.
> >
> >  crypto/crypto_user.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/crypto/crypto_user.c b/crypto/crypto_user.c
> > index 1512e41..bc7c4b5 100644
> > --- a/crypto/crypto_user.c
> > +++ b/crypto/crypto_user.c
> > @@ -460,7 +460,7 @@ static int crypto_user_rcv_msg(struct sk_buff *skb, struct nlmsghdr *nlh)
> >       int type, err;
> >
> >       type = nlh->nlmsg_type;
> > -     if (type > CRYPTO_MSG_MAX)
> > +     if (type < CRYPTO_MSG_BASE || type > CRYPTO_MSG_MAX)
> >               return -EINVAL;
>
> Adding a check here is obviously harmless but I think this is only
> called from netlink_rcv_skb() which already checks:
>
>         if (nlh->nlmsg_type < NLMSG_MIN_TYPE)
>                 goto ack;
>
> NLMSG_MIN_TYPE is 0x10 as well, so I don't think we can hit your
> condition.
>
> Your patch freaked me out a little because this is one of the bugs that
> I should have caught throught static analysis.

BUILD_BUG_ON(NLMSG_MIN_TYPE != CRYPTO_MSG_BASE) might be a better
thing to add, then.

I don't feel so bad for missing this.

>
> regards,
> dan carpenter
>
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