linux-kernel - Re: [Linux-kernel-mentees] [PATCH net] ipvs: Fix uninit-value in do_ip_vs_set

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Message-ID: <20200811050929.GA821443@PWN>
Date:   Tue, 11 Aug 2020 01:09:29 -0400
From:   Peilin Ye <yepeilin.cs@...il.com>
To:     Cong Wang <xiyou.wangcong@...il.com>
Cc:     Wensong Zhang <wensong@...ux-vs.org>,
        Simon Horman <horms@...ge.net.au>,
        Julian Anastasov <ja@....bg>,
        Pablo Neira Ayuso <pablo@...filter.org>,
        Jozsef Kadlecsik <kadlec@...filter.org>,
        Florian Westphal <fw@...len.de>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        lvs-devel@...r.kernel.org,
        NetFilter <netfilter-devel@...r.kernel.org>,
        coreteam@...filter.org,
        linux-kernel-mentees@...ts.linuxfoundation.org,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [Linux-kernel-mentees] [PATCH net] ipvs: Fix uninit-value in
 do_ip_vs_set_ctl()

On Mon, Aug 10, 2020 at 08:57:19PM -0700, Cong Wang wrote:
> On Mon, Aug 10, 2020 at 3:10 PM Peilin Ye <yepeilin.cs@...il.com> wrote:
> >
> > do_ip_vs_set_ctl() is referencing uninitialized stack value when `len` is
> > zero. Fix it.
> 
> Which exact 'cmd' is it here?
> 
> I _guess_ it is one of those uninitialized in set_arglen[], which is 0.

Yes, it was `IP_VS_SO_SET_NONE`, implicitly initialized to zero.

> But if that is the case, should it be initialized to
> sizeof(struct ip_vs_service_user) instead because ip_vs_copy_usvc_compat()
> is called anyway. Or, maybe we should just ban len==0 case.

I see. I think the latter would be easier, but we cannot ban all of
them, since the function does something with `IP_VS_SO_SET_FLUSH`, which
is a `len == 0` case.

Maybe we do something like this?

@@ -2432,6 +2432,8 @@ do_ip_vs_set_ctl(struct sock *sk, int cmd, void __user *user, unsigned int len)

 	if (cmd < IP_VS_BASE_CTL || cmd > IP_VS_SO_SET_MAX)
 		return -EINVAL;
+	if (len == 0 && cmd != IP_VS_SO_SET_FLUSH)
+		return -EINVAL;
 	if (len != set_arglen[CMDID(cmd)]) {
 		IP_VS_DBG(1, "set_ctl: len %u != %u\n",
 			  len, set_arglen[CMDID(cmd)]);
@@ -2547,9 +2549,6 @@ do_ip_vs_set_ctl(struct sock *sk, int cmd, void __user *user, unsigned int len)
 		break;
 	case IP_VS_SO_SET_DELDEST:
 		ret = ip_vs_del_dest(svc, &udest);
-		break;
-	default:
-		ret = -EINVAL;
 	}

   out_unlock:

Thank you,
Peilin Ye

> In either case, it does not look like you fix it correctly.
> 
> Thanks.