Commit d214c753 authored Nov 20, 2008 by Pablo Neira Ayuso Committed by David S. Miller Nov 20, 2008

filter: add SKF_AD_NLATTR_NEST to look for nested attributes



SKF_AD_NLATTR allows us to find the first matching attribute in a
stream of netlink attributes from one offset to the end of the
netlink message. This is not suitable to look for a specific
matching inside a set of nested attributes.

For example, in ctnetlink messages, if we look for the CTA_V6_SRC
attribute in a message that talks about an IPv4 connection,
SKF_AD_NLATTR returns the offset of CTA_STATUS which has the same
value of CTA_V6_SRC but outside the nest. To differenciate
CTA_STATUS and CTA_V6_SRC, we would have to make assumptions on the
size of the attribute and the usual offset, resulting in horrible
BSF code.

This patch adds SKF_AD_NLATTR_NEST, which is a variant of
SKF_AD_NLATTR, that looks for an attribute inside the limits of
a nested attributes, but not further.

This patch validates that we have enough room to look for the
nested attributes - based on a suggestion from Patrick McHardy.

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Acked-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent 68fd9910

include/linux/filter.h

+2 −1

Original line number	Diff line number	Diff line
		@@ -122,7 +122,8 @@ struct sock_fprog /* Required for SO_ATTACH_FILTER. */
		#define SKF_AD_PKTTYPE 4
		#define SKF_AD_IFINDEX 8
		#define SKF_AD_NLATTR 12
		#define SKF_AD_MAX 16
		#define SKF_AD_NLATTR_NEST 16
		#define SKF_AD_MAX 20
		#define SKF_NET_OFF (-0x100000)
		#define SKF_LL_OFF (-0x200000)

net/core/filter.c

+19 −0

Original line number	Diff line number	Diff line
		@@ -319,6 +319,25 @@ load_b:
		A = 0;
		continue;
		}
		case SKF_AD_NLATTR_NEST: {
		struct nlattr *nla;

		if (skb_is_nonlinear(skb))
		return 0;
		if (A > skb->len - sizeof(struct nlattr))
		return 0;

		nla = (struct nlattr *)&skb->data[A];
		if (nla->nla_len > A - skb->len)
		return 0;

		nla = nla_find_nested(nla, X);
		if (nla)
		A = (void )nla - (void )skb->data;
		else
		A = 0;
		continue;
		}
		default:
		return 0;
		}

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