[PATCH V2] netfilter: h323: avoid potential attack

[PATCH V2] netfilter: h323: avoid potential attack

[Zhouyi Zhou]

Thanks Eric for your review and advice.

I think hackers chould build a malicious h323 packet to overflow
the pointer p which will panic during the memcpy(addr, p, len)

For example, he may fabricate a very large taddr->ipAddress.ip;

Signed-off-by: Zhouyi Zhou <yizhouzhou@ict.ac.cn>
---
 net/netfilter/nf_conntrack_h323_main.c |    7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/net/netfilter/nf_conntrack_h323_main.c b/net/netfilter/nf_conntrack_h323_main.c
index 9511af0..ccd08c5 100644
--- a/net/netfilter/nf_conntrack_h323_main.c
+++ b/net/netfilter/nf_conntrack_h323_main.c
@@ -110,6 +110,7 @@ int (*nat_q931_hook) (struct sk_buff *skb,
 
 static DEFINE_SPINLOCK(nf_h323_lock);
 static char *h323_buffer;
+#define CHECK_BOUND(p, n) ((void *)p + n - (void *)h323_buffer > 65536)
 
 static struct nf_conntrack_helper nf_conntrack_helper_h245;
 static struct nf_conntrack_helper nf_conntrack_helper_q931[];
@@ -247,6 +248,9 @@ static int get_h245_addr(struct nf_conn *ct, const unsigned char *data,
 		return 0;
 	}
 
+	if (CHECK_BOUND(p, len + sizeof(__be16)))
+		return 0;
+
 	memcpy(addr, p, len);
 	memset((void *)addr + len, 0, sizeof(*addr) - len);
 	memcpy(port, p + len, sizeof(__be16));
@@ -669,6 +673,9 @@ int get_h225_addr(struct nf_conn *ct, unsigned char *data,
 		return 0;
 	}
 
+	if (CHECK_BOUND(p, len + sizeof(__be16)))
+		return 0;
+
 	memcpy(addr, p, len);
 	memset((void *)addr + len, 0, sizeof(*addr) - len);
 	memcpy(port, p + len, sizeof(__be16));
-- 
1.7.10.4

Re: Re: [PATCH V2] netfilter: h323: avoid potential attack

[Zhouyi Zhou]

Thanks Eric for replying
> -----Original Messages-----
> From: "Eric Dumazet" <eric.dumazet@gmail.com>
> Sent Time: Thursday, January 28, 2016
> To: "Zhouyi Zhou" <zhouzhouyi@gmail.com>
> Cc: pablo@netfilter.org, kaber@trash.net, kadlec@blackhole.kfki.hu, davem@davemloft.net, netfilter-devel@vger.kernel.org, coreteam@netfilter.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.or, "Zhouyi Zhou" <yizhouzhou@ict.ac.cn>
> Subject: Re: [PATCH V2] netfilter: h323: avoid potential attack
> 
> On Thu, 2016-01-28 at 16:59 +0800, Zhouyi Zhou wrote:
> > Thanks Eric for your review and advice.
> > 
> > I think hackers chould build a malicious h323 packet to overflow
> > the pointer p which will panic during the memcpy(addr, p, len)
> > 
> > For example, he may fabricate a very large taddr->ipAddress.ip;
> > 
> > Signed-off-by: Zhouyi Zhou <yizhouzhou@ict.ac.cn>
> > ---
> 
> Except you did not address my feedback about potentially reading not
> initialized memory.
> 
> if the frame length was 1000 bytes, then surely accessing memory at
> offset 8000 will either read garbage, or read data from a prior frame
> and leak secrets.
My patch is intend to prevent kernel panic, to prevent reading garbage
or read data from a prior frame and leak secrets, the prototypes of the 
get_h2x5_addr functions and the functions that call get_h2x5_addr should
be changed, should we do this? 
> 
> 
> 
Cheers 
Zhouyi

Re: Re: [PATCH V2] netfilter: h323: avoid potential attack

[Eric Dumazet]

On Thu, 2016-01-28 at 21:14 +0800, Zhouyi Zhou wrote:

> My patch is intend to prevent kernel panic, to prevent reading garbage
> or read data from a prior frame and leak secrets, the prototypes of the 
> get_h2x5_addr functions and the functions that call get_h2x5_addr should
> be changed, should we do this? 

In term of security, panics are better than allowing attacker to read
data from other people, like a password.

BTW, are you able to trigger any panic ?

I am not familiar with this code, it is not obvious.

If a fix is needed, better doing it right.

Re: [PATCH V2] netfilter: h323: avoid potential attack

[One Thousand Gnomes]

On Thu, 28 Jan 2016 06:00:50 -0800
Eric Dumazet <eric.dumazet@gmail.com> wrote:

> On Thu, 2016-01-28 at 21:14 +0800, Zhouyi Zhou wrote:
> 
> > My patch is intend to prevent kernel panic, to prevent reading garbage
> > or read data from a prior frame and leak secrets, the prototypes of the 
> > get_h2x5_addr functions and the functions that call get_h2x5_addr should
> > be changed, should we do this?   
> 
> In term of security, panics are better than allowing attacker to read
> data from other people, like a password.
> 
> BTW, are you able to trigger any panic ?

We have a smattering of panics in this code in bugzilla going back years.

https://bugzilla.kernel.org/show_bug.cgi?id=12473

etc

Alan