netdev - RE: [PATCH 25/26] net: pass a sockptr

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Date:   Fri, 7 Aug 2020 09:18:03 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Eric Dumazet' <eric.dumazet@...il.com>,
        Christoph Hellwig <hch@....de>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Alexey Kuznetsov <kuznet@....inr.ac.ru>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        Eric Dumazet <edumazet@...gle.com>
CC:     "linux-crypto@...r.kernel.org" <linux-crypto@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "bpf@...r.kernel.org" <bpf@...r.kernel.org>,
        "netfilter-devel@...r.kernel.org" <netfilter-devel@...r.kernel.org>,
        "coreteam@...filter.org" <coreteam@...filter.org>,
        "linux-sctp@...r.kernel.org" <linux-sctp@...r.kernel.org>,
        "linux-hams@...r.kernel.org" <linux-hams@...r.kernel.org>,
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        <bridge@...ts.linux-foundation.org>,
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        "dccp@...r.kernel.org" <dccp@...r.kernel.org>,
        "linux-decnet-user@...ts.sourceforge.net" 
        <linux-decnet-user@...ts.sourceforge.net>,
        "linux-wpan@...r.kernel.org" <linux-wpan@...r.kernel.org>,
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        "rds-devel@....oracle.com" <rds-devel@....oracle.com>,
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        <tipc-discussion@...ts.sourceforge.net>,
        "linux-x25@...r.kernel.org" <linux-x25@...r.kernel.org>,
        Stefan Schmidt <stefan@...enfreihafen.org>
Subject: RE: [PATCH 25/26] net: pass a sockptr_t into ->setsockopt

From: Eric Dumazet
> Sent: 06 August 2020 23:21
> 
> On 7/22/20 11:09 PM, Christoph Hellwig wrote:
> > Rework the remaining setsockopt code to pass a sockptr_t instead of a
> > plain user pointer.  This removes the last remaining set_fs(KERNEL_DS)
> > outside of architecture specific code.
> >
> > Signed-off-by: Christoph Hellwig <hch@....de>
> > Acked-by: Stefan Schmidt <stefan@...enfreihafen.org> [ieee802154]
> > ---
> 
> 
> ...
> 
> > diff --git a/net/ipv6/raw.c b/net/ipv6/raw.c
> > index 594e01ad670aa6..874f01cd7aec42 100644
> > --- a/net/ipv6/raw.c
> > +++ b/net/ipv6/raw.c
> > @@ -972,13 +972,13 @@ static int rawv6_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
> >  }
> >
> 
> ...
> 
> >  static int do_rawv6_setsockopt(struct sock *sk, int level, int optname,
> > -			    char __user *optval, unsigned int optlen)
> > +			       sockptr_t optval, unsigned int optlen)
> >  {
> >  	struct raw6_sock *rp = raw6_sk(sk);
> >  	int val;
> >
> > -	if (get_user(val, (int __user *)optval))
> > +	if (copy_from_sockptr(&val, optval, sizeof(val)))
> >  		return -EFAULT;
> >
> 
> converting get_user(...)   to  copy_from_sockptr(...) really assumed the optlen
> has been validated to be >= sizeof(int) earlier.
> 
> Which is not always the case, for example here.
> 
> User application can fool us passing optlen=0, and a user pointer of exactly TASK_SIZE-1

Won't the user pointer force copy_from_sockptr() to call
copy_from_user() which will then do access_ok() on the entire
range and so return -EFAULT.

The only problems arise if the kernel code adds an offset to the
user address.
And the later patch added an offset to the copy functions.

	David

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