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[SKFILTER]: Add SKF_ADF_NLATTR instruction
SKF_ADF_NLATTR searches for a netlink attribute, which avoids manually parsing and walking attributes. It takes the offset at which to start searching in the 'A' register and the attribute type in the 'X' register and returns the offset in the 'A' register. When the attribute is not found it returns zero. A top-level attribute can be located using a filter like this (example for nfnetlink, using struct nfgenmsg): ... { /* A = offset of first attribute */ .code = BPF_LD | BPF_IMM, .k = sizeof(struct nlmsghdr) + sizeof(struct nfgenmsg) }, { /* X = CTA_PROTOINFO */ .code = BPF_LDX | BPF_IMM, .k = CTA_PROTOINFO, }, { /* A = netlink attribute offset */ .code = BPF_LD | BPF_B | BPF_ABS, .k = SKF_AD_OFF + SKF_AD_NLATTR }, { /* Exit if not found */ .code = BPF_JMP | BPF_JEQ | BPF_K, .k = 0, .jt = <error> }, ... A nested attribute below the CTA_PROTOINFO attribute would then be parsed like this: ... { /* A += sizeof(struct nlattr) */ .code = BPF_ALU | BPF_ADD | BPF_K, .k = sizeof(struct nlattr), }, { /* X = CTA_PROTOINFO_TCP */ .code = BPF_LDX | BPF_IMM, .k = CTA_PROTOINFO_TCP, }, { /* A = netlink attribute offset */ .code = BPF_LD | BPF_B | BPF_ABS, .k = SKF_AD_OFF + SKF_AD_NLATTR }, ... The data of an attribute can be loaded into 'A' like this: ... { /* X = A (attribute offset) */ .code = BPF_MISC | BPF_TAX, }, { /* A = skb->data[X + k] */ .code = BPF_LD | BPF_B | BPF_IND, .k = sizeof(struct nlattr), }, ... Signed-off-by: Patrick McHardy <kaber@trash.net> Signed-off-by: David S. Miller <davem@davemloft.net>
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@ -121,7 +121,8 @@ struct sock_fprog /* Required for SO_ATTACH_FILTER. */
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#define SKF_AD_PROTOCOL 0
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#define SKF_AD_PKTTYPE 4
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#define SKF_AD_IFINDEX 8
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#define SKF_AD_MAX 12
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#define SKF_AD_NLATTR 12
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#define SKF_AD_MAX 16
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#define SKF_NET_OFF (-0x100000)
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#define SKF_LL_OFF (-0x200000)
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@ -27,6 +27,7 @@
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#include <linux/if_packet.h>
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#include <net/ip.h>
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#include <net/protocol.h>
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#include <net/netlink.h>
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#include <linux/skbuff.h>
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#include <net/sock.h>
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#include <linux/errno.h>
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@ -303,6 +304,22 @@ unsigned int sk_run_filter(struct sk_buff *skb, struct sock_filter *filter, int
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case SKF_AD_IFINDEX:
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A = skb->dev->ifindex;
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continue;
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case SKF_AD_NLATTR: {
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struct nlattr *nla;
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if (skb_is_nonlinear(skb))
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return 0;
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if (A > skb->len - sizeof(struct nlattr))
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return 0;
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nla = nla_find((struct nlattr *)&skb->data[A],
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skb->len - A, X);
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if (nla)
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A = (void *)nla - (void *)skb->data;
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else
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A = 0;
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continue;
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}
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default:
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return 0;
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}
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