netdev - RE: [net] tipc: fix uninit-value in tipc_nl_node_reset_link

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Date:   Thu, 7 Jul 2022 00:22:06 +0000
From:   Hoang Huu Le <hoang.h.le@...tech.com.au>
To:     Jakub Kicinski <kuba@...nel.org>
CC:     "jmaloy@...hat.com" <jmaloy@...hat.com>,
        "maloy@...jonn.com" <maloy@...jonn.com>,
        "ying.xue@...driver.com" <ying.xue@...driver.com>,
        Tung Quang Nguyen <tung.q.nguyen@...tech.com.au>,
        "pabeni@...hat.com" <pabeni@...hat.com>,
        "edumazet@...gle.com" <edumazet@...gle.com>,
        "tipc-discussion@...ts.sourceforge.net" 
        <tipc-discussion@...ts.sourceforge.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "syzbot+a73d24a22eeeebe5f244@...kaller.appspotmail.com" 
        <syzbot+a73d24a22eeeebe5f244@...kaller.appspotmail.com>
Subject: RE: [net] tipc: fix uninit-value in tipc_nl_node_reset_link_stats

> -----Original Message-----
> From: Jakub Kicinski <kuba@...nel.org>
> Sent: Thursday, July 7, 2022 3:34 AM
> To: Hoang Huu Le <hoang.h.le@...tech.com.au>
> Cc: jmaloy@...hat.com; maloy@...jonn.com; ying.xue@...driver.com; Tung Quang Nguyen <tung.q.nguyen@...tech.com.au>;
> pabeni@...hat.com; edumazet@...gle.com; tipc-discussion@...ts.sourceforge.net; netdev@...r.kernel.org;
> davem@...emloft.net; syzbot+a73d24a22eeeebe5f244@...kaller.appspotmail.com
> Subject: Re: [net] tipc: fix uninit-value in tipc_nl_node_reset_link_stats
> 
> On Wed,  6 Jul 2022 10:47:52 +0700 Hoang Le wrote:
> > diff --git a/net/tipc/node.c b/net/tipc/node.c
> > index b48d97cbbe29..80885780caa2 100644
> > --- a/net/tipc/node.c
> > +++ b/net/tipc/node.c
> > @@ -2574,8 +2574,10 @@ int tipc_nl_node_reset_link_stats(struct sk_buff *skb, struct genl_info *info)
> >  	if (!attrs[TIPC_NLA_LINK_NAME])
> >  		return -EINVAL;
> >
> > -	link_name = nla_data(attrs[TIPC_NLA_LINK_NAME]);
> > +	if (nla_len(attrs[TIPC_NLA_LINK_NAME]) <= 0)
> > +		return -EINVAL;
> >
> > +	link_name = nla_data(attrs[TIPC_NLA_LINK_NAME]);
> >  	err = -EINVAL;
> >  	if (!strcmp(link_name, tipc_bclink_name)) {
> >  		err = tipc_bclink_reset_stats(net, tipc_bc_sndlink(net));
> 
> I think you misunderstood me. Let me try to explain in more detail.
> 
> AFAICT the attrs in this function get validated using the
> tipc_nl_link_policy:
> 
> https://elixir.bootlin.com/linux/v5.19-rc4/source/net/tipc/node.c#L2567
> 
> This policy specifies the type for TIPC_NLA_LINK_NAME as NLA_STRING:
> 
> https://elixir.bootlin.com/linux/v5.19-rc4/source/net/tipc/netlink.c#L91
> 
> Therefore we can assume that the attribute is a valid (but not
> necessarily null-terminated) string. Otherwise
> nla_parse_nested_deprecated() would have returned an error.
> 
> The code for NLA_STRING validation is here:
> 
> https://elixir.bootlin.com/linux/v5.19-rc4/source/lib/nlattr.c#L437
> 
> So we can already assume that the attribute is not empty.
> 
> The bug you're fixing is that the string is not null-terminated,
> so strcmp() can read past the end of the attribute.
> 
No, I'm trying to fix below issues:

BUG: KMSAN: uninit-value in strlen lib/string.c:495 [inline]
BUG: KMSAN: uninit-value in strstr+0xb4/0x2e0 lib/string.c:840
 strlen lib/string.c:495 [inline]
 strstr+0xb4/0x2e0 lib/string.c:840
 tipc_nl_node_reset_link_stats+0x41e/0xba0 net/tipc/node.c:2582

I assume the link name attribute is empty as root cause. 
So, just checking length is enough for fixing this issue.

> What I was trying to suggest is that you change the policy from
> NLA_STRING to NLA_NUL_STRING, which also checks that the string
> is NULL-terminated.
> 
> Please note that it'd be a slight uAPI change, and could break
> applications which expect kernel to not require null-termination.
> Perhaps tipc developers can guide us on how likely that is.
> Alternative is to use strncmp(..., nla_len(attr)).