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pktbuff(3) libnetfilter_queue pktbuff(3)

NAME

pktbuff - User-space network packet buffer

SYNOPSIS

Modules


Other functions

Functions


struct pkt_buff * pktb_alloc (int family, void *data, size_t len, size_t extra)
uint8_t * pktb_data (struct pkt_buff *pktb)
uint32_t pktb_len (struct pkt_buff *pktb)
void pktb_free (struct pkt_buff *pktb)
int pktb_mangle (struct pkt_buff *pktb, int dataoff, unsigned int match_offset, unsigned int match_len, const char *rep_buffer, unsigned int rep_len)
bool pktb_mangled (const struct pkt_buff *pktb)

Detailed Description

This library provides the user-space network packet buffer. This abstraction is strongly inspired by Linux kernel network buffer, the so-called sk_buff.

Function Documentation

struct pkt_buff* pktb_alloc (int family, void * data, size_t len, size_t extra)

pktb_alloc - allocate a new packet buffer

Parameters

family Indicate what family. Currently supported families are AF_BRIDGE, AF_INET & AF_INET6.
data Pointer to packet data
len Packet length
extra Extra memory in the tail to be allocated (for mangling)

This function returns a packet buffer that contains the packet data and some extra memory room in the tail (if requested).

Returns

Pointer to a new userspace packet buffer or NULL on failure.

Errors

ENOMEM From calloc()
EPROTONOSUPPORT family was AF_BRIDGE and this is not an IP packet (v4 or v6)

See also

calloc(3)

Definition at line 52 of file pktbuff.c.

uint8_t* pktb_data (struct pkt_buff * pktb)

pktb_data - get pointer to network packet

Parameters

pktb Pointer to userspace packet buffer

Returns

Pointer to start of network packet data within pktb

It is appropriate to use pktb_data as the second argument of nfq_nlmsg_verdict_put_pkt()

Definition at line 105 of file pktbuff.c.

void pktb_free (struct pkt_buff * pktb)

pktb_free - release packet buffer

Parameters

pktb Pointer to userspace packet buffer

Definition at line 129 of file pktbuff.c.

uint32_t pktb_len (struct pkt_buff * pktb)

pktb_len - get length of packet buffer

Parameters

pktb Pointer to userspace packet buffer

Returns

Length of packet contained within pktb

It is appropriate to use pktb_len as the third argument of nfq_nlmsg_verdict_put_pkt()

Definition at line 119 of file pktbuff.c.

int pktb_mangle (struct pkt_buff * pktb, int dataoff, unsigned int match_offset, unsigned int match_len, const char * rep_buffer, unsigned int rep_len)

pktb_mangle - adjust contents of a packet

Parameters

pktb Pointer to userspace packet buffer
dataoff Supplementary offset, usually offset from layer 3 (IP) header to the layer 4 (TCP or UDP) header. Specify zero to access the layer 3 header. If pktb was created in family AF_BRIDGE, specify -ETH_HLEN (a negative offset) to access the layer 2 (MAC) header.
match_offset Further offset to content that you want to mangle
match_len Length of the existing content you want to mangle
rep_buffer Pointer to data you want to use to replace current content
rep_len Length of data you want to use to replace current content

Returns

1 for success and 0 for failure. Failure will occur if the extra argument to the pktb_alloc() call that created pktb is less than the excess of rep_len over match_len

Warning

pktb_mangle does not update any checksums. Developers should use the appropriate mangler for the protocol level: nfq_ip_mangle(), nfq_tcp_mangle_ipv4() or nfq_udp_mangle_ipv4(). IPv6 versions are planned.
It is appropriate to use pktb_mangle to change the MAC header.

Definition at line 314 of file pktbuff.c.

bool pktb_mangled (const struct pkt_buff * pktb)

pktb_mangled - test whether packet has been mangled

Parameters

pktb Pointer to userspace packet buffer

Returns

true if packet has been mangled (modified), else false

When assembling a verdict, it is not necessary to return the contents of un-modified packets. Use pktb_mangled to decide whether packet contents need to be returned.

Definition at line 359 of file pktbuff.c.

Author

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Thu Jan 28 2021 Version 1.0.5