pktbuff(3)

📦
version 1.0.5 · 5 versions
, in ubuntu noble, ubuntu questing

💖 pktbuff — the user-space network packet buffer 💖

okay bestie, so pktbuff is a library function set from libnetfilter_queue and it's literally the moment your packets get a lil home in userspace 🏠✨

✨ 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 hands you the user-space network packet buffer. The whole abstraction is strongly inspired by the Linux kernel network buffer — you know, the one and only sk_buff 👑 iykyk.

🌈 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 — tell it which family you're on. Currently supported families are AF_BRIDGE, AF_INET & AF_INET6. periodt.
  • 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 ✂️✨ (glow up but for bytes)

Parameters

  • pktb — pointer to userspace packet buffer
  • dataoff — supplementary offset, usually the offset from the 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 🚨 bestie listen to me: 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. lowkey efficient 💅

Definition at line 359 of file pktbuff.c.

👑 Author 👑

Generated automatically by Doxygen for libnetfilter_queue from the source code. no cap, a robot wrote the author section and honestly? slay 🤖✨

and that's the whole page bestie 🫶 this was Version 1.0.5, dated with the libnetfilter_queue manpage energy, and yes the footer said pktbuff(3) too — go forth and mangle responsibly 🌸💖🧚

📦 where this page comes from