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filter: add SKF_AD_NLATTR_NEST to look for nested attributes

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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>
This commit is contained in:
Pablo Neira Ayuso 2008-11-20 00:49:27 -08:00 • committed by David S. Miller
commit d214c7537b
2 changed files with 21 additions and 1 deletions
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3
include/linux/filter.h
View file

@ -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)

19
net/core/filter.c
View file

@ -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;
}