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>
diff --git a/include/linux/filter.h b/include/linux/filter.h
index b6ea9aa..1354aaf 100644
--- a/include/linux/filter.h
+++ b/include/linux/filter.h
@@ -122,7 +122,8 @@
#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)
diff --git a/net/core/filter.c b/net/core/filter.c
index df37443..d1d779c 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -319,6 +319,25 @@
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;
}