Re: [PATCH 1/1] netfilter: h323: avoid potential attack
From: Eric Dumazet <hidden>
Date: 2016-01-27 15:57:50
Also in:
lkml, netfilter-devel
On Wed, 2016-01-27 at 22:40 +0800, Zhouyi Zhou wrote:
quoted hunk ↗ jump to hunk
From: Zhouyi Zhou <redacted> 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 <redacted> --- net/netfilter/nf_conntrack_h323_main.c | 8 ++++++++ 1 file changed, 8 insertions(+)diff --git a/net/netfilter/nf_conntrack_h323_main.c b/net/netfilter/nf_conntrack_h323_main.c index 9511af0..3b3dd8c 100644 --- a/net/netfilter/nf_conntrack_h323_main.c +++ b/net/netfilter/nf_conntrack_h323_main.c@@ -110,6 +110,10 @@ int (*nat_q931_hook) (struct sk_buff *skb, static DEFINE_SPINLOCK(nf_h323_lock); static char *h323_buffer; +#define CHECK_BOUND(p, n) do { \ + if (((p - h323_buffer) + n) > 65536) \ + return 0; \ +} while (0)
Do not add 'return X;' or 'goto something;' in macros please. Even referring to 'h323_buffer' is not nice, and of course 65536 is another 'magic' value. Even if h323_buffer was allocated to hold 65536 bytes, the various skb_header_pointer() calls only populated a part of it. I understand there is a bad precedent in net/netfilter/nf_conntrack_h323_asn1.c, but it is not a good reason. Anyway, if the issue is real, you do not take into account the 2 extra bytes for the port. memcpy(port, p + len, sizeof(__be16));