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.
Signed-off-by: Pablo Neira Ayuso <pablo@xxxxxxxxxxxxx>
---
include/linux/filter.h | 3 ++-
net/core/filter.c | 15 +++++++++++++++
2 files changed, 17 insertions(+), 1 deletions(-)
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 @@ 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)
diff --git a/net/core/filter.c b/net/core/filter.c
index df37443..2f9c7ea 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -319,6 +319,21 @@ 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 = nla_find_nested((struct nlattr *)&skb->data[A],X);
+ if (nla)
+ A = (void *)nla - (void *)skb->data;
+ else
+ A = 0;
+ continue;
+ }
default:
return 0;
}
--
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