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bpf: support sending packets on loopback interfaces 

Previously sending packets on a loopback interface via bpf failed
because the packets are treated as AF_UNSPEC by bpf and the loopback
interface couldn't handle such packets.

This fix enables user programs to prepend a protocol family (AF_INET or
AF_INET6) to a payload.  bpf interprets it and treats a packet as so,
not just AF_UNSPEC.  The protocol family is encoded as 4 bytes, host byte
order as per DLT_NULL in the specification(*).

(*) https://www.tcpdump.org/linktypes.html

Proposed on tech-net and tech-kern
This commit is contained in:
ozaki-r 2022-11-30 06:02:37 +00:00
parent d2296b0783
commit 39ce7d7534
1 changed files with 20 additions and 8 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

28
sys/net/bpf.c
View File

@ -1,4 +1,4 @@
/* $NetBSD: bpf.c,v 1.248 2022/11/19 08:53:06 yamt Exp $ */
/* $NetBSD: bpf.c,v 1.249 2022/11/30 06:02:37 ozaki-r Exp $ */
/*
* Copyright (c) 1990, 1991, 1993
@ -39,7 +39,7 @@
*/
#include <sys/cdefs.h>
__KERNEL_RCSID(0, "$NetBSD: bpf.c,v 1.248 2022/11/19 08:53:06 yamt Exp $");
__KERNEL_RCSID(0, "$NetBSD: bpf.c,v 1.249 2022/11/30 06:02:37 ozaki-r Exp $");
#if defined(_KERNEL_OPT)
#include "opt_bpf.h"
@ -89,6 +89,7 @@ __KERNEL_RCSID(0, "$NetBSD: bpf.c,v 1.248 2022/11/19 08:53:06 yamt Exp $");
#include <net/if_arc.h>
#include <net/if_ether.h>
#include <net/if_types.h>
#include <netinet/in.h>
#include <netinet/if_inarp.h>
@ -244,7 +245,7 @@ static void bpf_freed(struct bpf_d *);
static void bpf_free_filter(struct bpf_filter *);
static void bpf_ifname(struct ifnet *, struct ifreq *);
static void *bpf_mcpy(void *, const void *, size_t);
static int bpf_movein(struct uio *, int, uint64_t,
static int bpf_movein(struct ifnet *, struct uio *, int, uint64_t,
struct mbuf **, struct sockaddr *,
struct bpf_filter **);
static void bpf_attachd(struct bpf_d *, struct bpf_if *);
@ -323,7 +324,7 @@ bpf_jit_freecode(bpfjit_func_t jcode)
}
static int
bpf_movein(struct uio *uio, int linktype, uint64_t mtu, struct mbuf **mp,
bpf_movein(struct ifnet *ifp, struct uio *uio, int linktype, uint64_t mtu, struct mbuf **mp,
struct sockaddr *sockp, struct bpf_filter **wfilter)
{
struct mbuf *m, *m0, *n;
@ -385,7 +386,11 @@ bpf_movein(struct uio *uio, int linktype, uint64_t mtu, struct mbuf **mp,
case DLT_NULL:
sockp->sa_family = AF_UNSPEC;
hlen = 0;
if (ifp->if_type == IFT_LOOP) {
/* Set here to apply the following validations */
hlen = sizeof(uint32_t);
} else
hlen = 0;
align = 0;
break;
@ -441,8 +446,15 @@ bpf_movein(struct uio *uio, int linktype, uint64_t mtu, struct mbuf **mp,
}
if (hlen != 0) {
/* move link level header in the top of mbuf to sa_data */
memcpy(sockp->sa_data, mtod(m0, void *), hlen);
if (linktype == DLT_NULL && ifp->if_type == IFT_LOOP) {
uint32_t af;
/* the link header indicates the address family */
memcpy(&af, mtod(m0, void *), sizeof(af));
sockp->sa_family = af;
} else {
/* move link level header in the top of mbuf to sa_data */
memcpy(sockp->sa_data, mtod(m0, void *), hlen);
}
m0->m_data += hlen;
m0->m_len -= hlen;
}
@ -853,7 +865,7 @@ bpf_write(struct file *fp, off_t *offp, struct uio *uio,
goto out;
}
error = bpf_movein(uio, (int)bp->bif_dlt, ifp->if_mtu, &m,
error = bpf_movein(ifp, uio, (int)bp->bif_dlt, ifp->if_mtu, &m,
(struct sockaddr *) &dst, &d->bd_wfilter);
if (error)
goto out;