- 根目录:
- net
- ipv4
- netfilter
- nf_nat_snmp_basic.c
/*
* nf_nat_snmp_basic.c
*
* Basic SNMP Application Layer Gateway
*
* This IP NAT module is intended for use with SNMP network
* discovery and monitoring applications where target networks use
* conflicting private address realms.
*
* Static NAT is used to remap the networks from the view of the network
* management system at the IP layer, and this module remaps some application
* layer addresses to match.
*
* The simplest form of ALG is performed, where only tagged IP addresses
* are modified. The module does not need to be MIB aware and only scans
* messages at the ASN.1/BER level.
*
* Currently, only SNMPv1 and SNMPv2 are supported.
*
* More information on ALG and associated issues can be found in
* RFC 2962
*
* The ASB.1/BER parsing code is derived from the gxsnmp package by Gregory
* McLean & Jochen Friedrich, stripped down for use in the kernel.
*
* Copyright (c) 2000 RP Internet (www.rpi.net.au).
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
* You should have received a copy of the GNU General Public License
* along with this program; if not, see <http://www.gnu.org/licenses/>.
*
* Author: James Morris <jmorris@intercode.com.au>
*
* Copyright (c) 2006-2010 Patrick McHardy <kaber@trash.net>
*/
#include <linux/module.h>
#include <linux/moduleparam.h>
#include <linux/types.h>
#include <linux/kernel.h>
#include <linux/slab.h>
#include <linux/in.h>
#include <linux/ip.h>
#include <linux/udp.h>
#include <net/checksum.h>
#include <net/udp.h>
#include <net/netfilter/nf_nat.h>
#include <net/netfilter/nf_conntrack_expect.h>
#include <net/netfilter/nf_conntrack_helper.h>
#include <net/netfilter/nf_nat_helper.h>
#include <linux/netfilter/nf_conntrack_snmp.h>
MODULE_LICENSE("GPL");
MODULE_AUTHOR("James Morris <jmorris@intercode.com.au>");
MODULE_DESCRIPTION("Basic SNMP Application Layer Gateway");
MODULE_ALIAS("ip_nat_snmp_basic");
#define SNMP_PORT 161
#define SNMP_TRAP_PORT 162
#define NOCT1(n) (*(u8 *)(n))
static int debug;
static DEFINE_SPINLOCK(snmp_lock);
/*
* Application layer address mapping mimics the NAT mapping, but
* only for the first octet in this case (a more flexible system
* can be implemented if needed).
*/
struct oct1_map
{
u_int8_t from;
u_int8_t to;
};
/*****************************************************************************
*
* Basic ASN.1 decoding routines (gxsnmp author Dirk Wisse)
*
*****************************************************************************/
/* Class */
#define ASN1_UNI 0 /* Universal */
#define ASN1_APL 1 /* Application */
#define ASN1_CTX 2 /* Context */
#define ASN1_PRV 3 /* Private */
/* Tag */
#define ASN1_EOC 0 /* End Of Contents */
#define ASN1_BOL 1 /* Boolean */
#define ASN1_INT 2 /* Integer */
#define ASN1_BTS 3 /* Bit String */
#define ASN1_OTS 4 /* Octet String */
#define ASN1_NUL 5 /* Null */
#define ASN1_OJI 6 /* Object Identifier */
#define ASN1_OJD 7 /* Object Description */
#define ASN1_EXT 8 /* External */
#define ASN1_SEQ 16 /* Sequence */
#define ASN1_SET 17 /* Set */
#define ASN1_NUMSTR 18 /* Numerical String */
#define ASN1_PRNSTR 19 /* Printable String */
#define ASN1_TEXSTR 20 /* Teletext String */
#define ASN1_VIDSTR 21 /* Video String */
#define ASN1_IA5STR 22 /* IA5 String */
#define ASN1_UNITIM 23 /* Universal Time */
#define ASN1_GENTIM 24 /* General Time */
#define ASN1_GRASTR 25 /* Graphical String */
#define ASN1_VISSTR 26 /* Visible String */
#define ASN1_GENSTR 27 /* General String */
/* Primitive / Constructed methods*/
#define ASN1_PRI 0 /* Primitive */
#define ASN1_CON 1 /* Constructed */
/*
* Error codes.
*/
#define ASN1_ERR_NOERROR 0
#define ASN1_ERR_DEC_EMPTY 2
#define ASN1_ERR_DEC_EOC_MISMATCH 3
#define ASN1_ERR_DEC_LENGTH_MISMATCH 4
#define ASN1_ERR_DEC_BADVALUE 5
/*
* ASN.1 context.
*/
struct asn1_ctx
{
int error; /* Error condition */
unsigned char *pointer; /* Octet just to be decoded */
unsigned char *begin; /* First octet */
unsigned char *end; /* Octet after last octet */
};
/*
* Octet string (not null terminated)
*/
struct asn1_octstr
{
unsigned char *data;
unsigned int len;
};
static void asn1_open(struct asn1_ctx *ctx,
unsigned char *buf,
unsigned int len)
{
ctx->begin = buf;
ctx->end = buf + len;
ctx->pointer = buf;
ctx->error = ASN1_ERR_NOERROR;
}
static unsigned char asn1_octet_decode(struct asn1_ctx *ctx, unsigned char *ch)
{
if (ctx->pointer >= ctx->end) {
ctx->error = ASN1_ERR_DEC_EMPTY;
return 0;
}
*ch = *(ctx->pointer)++;
return 1;
}
static unsigned char asn1_tag_decode(struct asn1_ctx *ctx, unsigned int *tag)
{
unsigned char ch;
*tag = 0;
do
{
if (!asn1_octet_decode(ctx, &ch))
return 0;
*tag <<= 7;
*tag |= ch & 0x7F;
} while ((ch & 0x80) == 0x80);
return 1;
}
static unsigned char asn1_id_decode(struct asn1_ctx *ctx,
unsigned int *cls,
unsigned int *con,
unsigned int *tag)
{
unsigned char ch;
if (!asn1_octet_decode(ctx, &ch))
return 0;
*cls = (ch & 0xC0) >> 6;
*con = (ch & 0x20) >> 5;
*tag = (ch & 0x1F);
if (*tag == 0x1F) {
if (!asn1_tag_decode(ctx, tag))
return 0;
}
return 1;
}
static unsigned char asn1_length_decode(struct asn1_ctx *ctx,
unsigned int *def,
unsigned int *len)
{
unsigned char ch, cnt;
if (!asn1_octet_decode(ctx, &ch))
return 0;
if (ch == 0x80)
*def = 0;
else {
*def = 1;
if (ch < 0x80)
*len = ch;
else {
cnt = ch & 0x7F;
*len = 0;
while (cnt > 0) {
if (!asn1_octet_decode(ctx, &ch))
return 0;
*len <<= 8;
*len |= ch;
cnt--;
}
}
}
/* don't trust len bigger than ctx buffer */
if (*len > ctx->end - ctx->pointer)
return 0;
return 1;
}
static unsigned char asn1_header_decode(struct asn1_ctx *ctx,
unsigned char **eoc,
unsigned int *cls,
unsigned int *con,
unsigned int *tag)
{
unsigned int def, len;
if (!asn1_id_decode(ctx, cls, con, tag))
return 0;
def = len = 0;
if (!asn1_length_decode(ctx, &def, &len))
return 0;
/* primitive shall be definite, indefinite shall be constructed */
if (*con == ASN1_PRI && !def)
return 0;
if (def)
*eoc = ctx->pointer + len;
else
*eoc = NULL;
return 1;
}
static unsigned char asn1_eoc_decode(struct asn1_ctx *ctx, unsigned char *eoc)
{
unsigned char ch;
if (eoc == NULL) {
if (!asn1_octet_decode(ctx, &ch))
return 0;
if (ch != 0x00) {
ctx->error = ASN1_ERR_DEC_EOC_MISMATCH;
return 0;
}
if (!asn1_octet_decode(ctx, &ch))
return 0;
if (ch != 0x00) {
ctx->error = ASN1_ERR_DEC_EOC_MISMATCH;
return 0;
}
return 1;
} else {
if (ctx->pointer != eoc) {
ctx->error = ASN1_ERR_DEC_LENGTH_MISMATCH;
return 0;
}
return 1;
}
}
static unsigned char asn1_null_decode(struct asn1_ctx *ctx, unsigned char *eoc)
{
ctx->pointer = eoc;
return 1;
}
static unsigned char asn1_long_decode(struct asn1_ctx *ctx,
unsigned char *eoc,
long *integer)
{
unsigned char ch;
unsigned int len;
if (!asn1_octet_decode(ctx, &ch))
return 0;
*integer = (signed char) ch;
len = 1;
while (ctx->pointer < eoc) {
if (++len > sizeof (long)) {
ctx->error = ASN1_ERR_DEC_BADVALUE;
return 0;
}
if (!asn1_octet_decode(ctx, &ch))
return 0;
*integer <<= 8;
*integer |= ch;
}
return 1;
}
static unsigned char asn1_uint_decode(struct asn1_ctx *ctx,
unsigned char *eoc,
unsigned int *integer)
{
unsigned char ch;
unsigned int len;
if (!asn1_octet_decode(ctx, &ch))
return 0;
*integer = ch;
if (ch == 0) len = 0;
else len = 1;
while (ctx->pointer < eoc) {
if (++len > sizeof (unsigned int)) {
ctx->error = ASN1_ERR_DEC_BADVALUE;
return 0;
}
if (!asn1_octet_decode(ctx, &ch))
return 0;
*integer <<= 8;
*integer |= ch;
}
return 1;
}
static unsigned char asn1_ulong_decode(struct asn1_ctx *ctx,
unsigned char *eoc,
unsigned long *integer)
{
unsigned char ch;
unsigned int len;
if (!asn1_octet_decode(ctx, &ch))
return 0;
*integer = ch;
if (ch == 0) len = 0;
else len = 1;
while (ctx->pointer < eoc) {
if (++len > sizeof (unsigned long)) {
ctx->error = ASN1_ERR_DEC_BADVALUE;
return 0;
}
if (!asn1_octet_decode(ctx, &ch))
return 0;
*integer <<= 8;
*integer |= ch;
}
return 1;
}
static unsigned char asn1_octets_decode(struct asn1_ctx *ctx,
unsigned char *eoc,
unsigned char **octets,
unsigned int *len)
{
unsigned char *ptr;
*len = 0;
*octets = kmalloc(eoc - ctx->pointer, GFP_ATOMIC);
if (*octets == NULL)
return 0;
ptr = *octets;
while (ctx->pointer < eoc) {
if (!asn1_octet_decode(ctx, ptr++)) {
kfree(*octets);
*octets = NULL;
return 0;
}
(*len)++;
}
return 1;
}
static unsigned char asn1_subid_decode(struct asn1_ctx *ctx,
unsigned long *subid)
{
unsigned char ch;
*subid = 0;
do {
if (!asn1_octet_decode(ctx, &ch))
return 0;
*subid <<= 7;
*subid |= ch & 0x7F;
} while ((ch & 0x80) == 0x80);
return 1;
}
static unsigned char asn1_oid_decode(struct asn1_ctx *ctx,
unsigned char *eoc,
unsigned long **oid,
unsigned int *len)
{
unsigned long subid;
unsigned long *optr;
size_t size;
size = eoc - ctx->pointer + 1;
/* first subid actually encodes first two subids */
if (size < 2 || size > ULONG_MAX/sizeof(unsigned long))
return 0;
*oid = kmalloc(size * sizeof(unsigned long), GFP_ATOMIC);
if (*oid == NULL)
return 0;
optr = *oid;
if (!asn1_subid_decode(ctx, &subid)) {
kfree(*oid);
*oid = NULL;
return 0;
}
if (subid < 40) {
optr[0] = 0;
optr[1] = subid;
} else if (subid < 80) {
optr[0] = 1;
optr[1] = subid - 40;
} else {
optr[0] = 2;
optr[1] = subid - 80;
}
*len = 2;
optr += 2;
while (ctx->pointer < eoc) {
if (++(*len) > size) {
ctx->error = ASN1_ERR_DEC_BADVALUE;
kfree(*oid);
*oid = NULL;
return 0;
}
if (!asn1_subid_decode(ctx, optr++)) {
kfree(*oid);
*oid = NULL;
return 0;
}
}
return 1;
}
/*****************************************************************************
*
* SNMP decoding routines (gxsnmp author Dirk Wisse)
*
*****************************************************************************/
/* SNMP Versions */
#define SNMP_V1 0
#define SNMP_V2C 1
#define SNMP_V2 2
#define SNMP_V3 3
/* Default Sizes */
#define SNMP_SIZE_COMM 256
#define SNMP_SIZE_OBJECTID 128
#define SNMP_SIZE_BUFCHR 256
#define SNMP_SIZE_BUFINT 128
#define SNMP_SIZE_SMALLOBJECTID 16
/* Requests */
#define SNMP_PDU_GET 0
#define SNMP_PDU_NEXT 1
#define SNMP_PDU_RESPONSE 2
#define SNMP_PDU_SET 3
#define SNMP_PDU_TRAP1 4
#define SNMP_PDU_BULK 5
#define SNMP_PDU_INFORM 6
#define SNMP_PDU_TRAP2 7
/* Errors */
#define SNMP_NOERROR 0
#define SNMP_TOOBIG 1
#define SNMP_NOSUCHNAME 2
#define SNMP_BADVALUE 3
#define SNMP_READONLY 4
#define SNMP_GENERROR 5
#define SNMP_NOACCESS 6
#define SNMP_WRONGTYPE 7
#define SNMP_WRONGLENGTH 8
#define SNMP_WRONGENCODING 9
#define SNMP_WRONGVALUE 10
#define SNMP_NOCREATION 11
#define SNMP_INCONSISTENTVALUE 12
#define SNMP_RESOURCEUNAVAILABLE 13
#define SNMP_COMMITFAILED 14
#define SNMP_UNDOFAILED 15
#define SNMP_AUTHORIZATIONERROR 16
#define SNMP_NOTWRITABLE 17
#define SNMP_INCONSISTENTNAME 18
/* General SNMP V1 Traps */
#define SNMP_TRAP_COLDSTART 0
#define SNMP_TRAP_WARMSTART 1
#define SNMP_TRAP_LINKDOWN 2
#define SNMP_TRAP_LINKUP 3
#define SNMP_TRAP_AUTFAILURE 4
#define SNMP_TRAP_EQPNEIGHBORLOSS 5
#define SNMP_TRAP_ENTSPECIFIC 6
/* SNMPv1 Types */
#define SNMP_NULL 0
#define SNMP_INTEGER 1 /* l */
#define SNMP_OCTETSTR 2 /* c */
#define SNMP_DISPLAYSTR 2 /* c */
#define SNMP_OBJECTID 3 /* ul */
#define SNMP_IPADDR 4 /* uc */
#define SNMP_COUNTER 5 /* ul */
#define SNMP_GAUGE 6 /* ul */
#define SNMP_TIMETICKS 7 /* ul */
#define SNMP_OPAQUE 8 /* c */
/* Additional SNMPv2 Types */
#define SNMP_UINTEGER 5 /* ul */
#define SNMP_BITSTR 9 /* uc */
#define SNMP_NSAP 10 /* uc */
#define SNMP_COUNTER64 11 /* ul */
#define SNMP_NOSUCHOBJECT 12
#define SNMP_NOSUCHINSTANCE 13
#define SNMP_ENDOFMIBVIEW 14
union snmp_syntax
{
unsigned char uc[0]; /* 8 bit unsigned */
char c[0]; /* 8 bit signed */
unsigned long ul[0]; /* 32 bit unsigned */
long l[0]; /* 32 bit signed */
};
struct snmp_object
{
unsigned long *id;
unsigned int id_len;
unsigned short type;
unsigned int syntax_len;
union snmp_syntax syntax;
};
struct snmp_request
{
unsigned long id;
unsigned int error_status;
unsigned int error_index;
};
struct snmp_v1_trap
{
unsigned long *id;
unsigned int id_len;
unsigned long ip_address; /* pointer */
unsigned int general;
unsigned int specific;
unsigned long time;
};
/* SNMP types */
#define SNMP_IPA 0
#define SNMP_CNT 1
#define SNMP_GGE 2
#define SNMP_TIT 3
#define SNMP_OPQ 4
#define SNMP_C64 6
/* SNMP errors */
#define SERR_NSO 0
#define SERR_NSI 1
#define SERR_EOM 2
static inline void mangle_address(unsigned char *begin,
unsigned char *addr,
const struct oct1_map *map,
__sum16 *check);
struct snmp_cnv
{
unsigned int class;
unsigned int tag;
int syntax;
};
static const struct snmp_cnv snmp_conv[] = {
{ASN1_UNI, ASN1_NUL, SNMP_NULL},
{ASN1_UNI, ASN1_INT, SNMP_INTEGER},
{ASN1_UNI, ASN1_OTS, SNMP_OCTETSTR},
{ASN1_UNI, ASN1_OTS, SNMP_DISPLAYSTR},
{ASN1_UNI, ASN1_OJI, SNMP_OBJECTID},
{ASN1_APL, SNMP_IPA, SNMP_IPADDR},
{ASN1_APL, SNMP_CNT, SNMP_COUNTER}, /* Counter32 */
{ASN1_APL, SNMP_GGE, SNMP_GAUGE}, /* Gauge32 == Unsigned32 */
{ASN1_APL, SNMP_TIT, SNMP_TIMETICKS},
{ASN1_APL, SNMP_OPQ, SNMP_OPAQUE},
/* SNMPv2 data types and errors */
{ASN1_UNI, ASN1_BTS, SNMP_BITSTR},
{ASN1_APL, SNMP_C64, SNMP_COUNTER64},
{ASN1_CTX, SERR_NSO, SNMP_NOSUCHOBJECT},
{ASN1_CTX, SERR_NSI, SNMP_NOSUCHINSTANCE},
{ASN1_CTX, SERR_EOM, SNMP_ENDOFMIBVIEW},
{0, 0, -1}
};
static unsigned char snmp_tag_cls2syntax(unsigned int tag,
unsigned int cls,
unsigned short *syntax)
{
const struct snmp_cnv *cnv;
cnv = snmp_conv;
while (cnv->syntax != -1) {
if (cnv->tag == tag && cnv->class == cls) {
*syntax = cnv->syntax;
return 1;
}
cnv++;
}
return 0;
}
static unsigned char snmp_object_decode(struct asn1_ctx *ctx,
struct snmp_object **obj)
{
unsigned int cls, con, tag, len, idlen;
unsigned short type;
unsigned char *eoc, *end, *p;
unsigned long *lp, *id;
unsigned long ul;
long l;
*obj = NULL;
id = NULL;
if (!asn1_header_decode(ctx, &eoc, &cls, &con, &tag))
return 0;
if (cls != ASN1_UNI || con != ASN1_CON || tag != ASN1_SEQ)
return 0;
if (!asn1_header_decode(ctx, &end, &cls, &con, &tag))
return 0;
if (cls != ASN1_UNI || con != ASN1_PRI || tag != ASN1_OJI)
return 0;
if (!asn1_oid_decode(ctx, end, &id, &idlen))
return 0;
if (!asn1_header_decode(ctx, &end, &cls, &con, &tag)) {
kfree(id);
return 0;
}
if (con != ASN1_PRI) {
kfree(id);
return 0;
}
type = 0;
if (!snmp_tag_cls2syntax(tag, cls, &type)) {
kfree(id);
return 0;
}
l = 0;
switch (type) {
case SNMP_INTEGER:
len = sizeof(long);
if (!asn1_long_decode(ctx, end, &l)) {
kfree(id);
return 0;
}
*obj = kmalloc(sizeof(struct snmp_object) + len, GFP_ATOMIC);
if (*obj == NULL) {
kfree(id);
return 0;
}
(*obj)->syntax.l[0] = l;
break;
case SNMP_OCTETSTR:
case SNMP_OPAQUE:
if (!asn1_octets_decode(ctx, end, &p, &len)) {
kfree(id);
return 0;
}
*obj = kmalloc(sizeof(struct snmp_object) + len, GFP_ATOMIC);
if (*obj == NULL) {
kfree(p);
kfree(id);
return 0;
}
memcpy((*obj)->syntax.c, p, len);
kfree(p);
break;
case SNMP_NULL:
case SNMP_NOSUCHOBJECT:
case SNMP_NOSUCHINSTANCE:
case SNMP_ENDOFMIBVIEW:
len = 0;
*obj = kmalloc(sizeof(struct snmp_object), GFP_ATOMIC);
if (*obj == NULL) {
kfree(id);
return 0;
}
if (!asn1_null_decode(ctx, end)) {
kfree(id);
kfree(*obj);
*obj = NULL;
return 0;
}
break;
case SNMP_OBJECTID:
if (!asn1_oid_decode(ctx, end, &lp, &len)) {
kfree(id);
return 0;
}
len *= sizeof(unsigned long);
*obj = kmalloc(sizeof(struct snmp_object) + len, GFP_ATOMIC);
if (*obj == NULL) {
kfree(lp);
kfree(id);
return 0;
}
memcpy((*obj)->syntax.ul, lp, len);
kfree(lp);
break;
case SNMP_IPADDR:
if (!asn1_octets_decode(ctx, end, &p, &len)) {
kfree(id);
return 0;
}
if (len != 4) {
kfree(p);
kfree(id);
return 0;
}
*obj = kmalloc(sizeof(struct snmp_object) + len, GFP_ATOMIC);
if (*obj == NULL) {
kfree(p);
kfree(id);
return 0;
}
memcpy((*obj)->syntax.uc, p, len);
kfree(p);
break;
case SNMP_COUNTER:
case SNMP_GAUGE:
case SNMP_TIMETICKS:
len = sizeof(unsigned long);
if (!asn1_ulong_decode(ctx, end, &ul)) {
kfree(id);
return 0;
}
*obj = kmalloc(sizeof(struct snmp_object) + len, GFP_ATOMIC);
if (*obj == NULL) {
kfree(id);
return 0;
}
(*obj)->syntax.ul[0] = ul;
break;
default:
kfree(id);
return 0;
}
(*obj)->syntax_len = len;
(*obj)->type = type;
(*obj)->id = id;
(*obj)->id_len = idlen;
if (!asn1_eoc_decode(ctx, eoc)) {
kfree(id);
kfree(*obj);
*obj = NULL;
return 0;
}
return 1;
}
static unsigned char snmp_request_decode(struct asn1_ctx *ctx,
struct snmp_request *request)
{
unsigned int cls, con, tag;
unsigned char *end;
if (!asn1_header_decode(ctx, &end, &cls, &con, &tag))
return 0;
if (cls != ASN1_UNI || con != ASN1_PRI || tag != ASN1_INT)
return 0;
if (!asn1_ulong_decode(ctx, end, &request->id))
return 0;
if (!asn1_header_decode(ctx, &end, &cls, &con, &tag))
return 0;
if (cls != ASN1_UNI || con != ASN1_PRI || tag != ASN1_INT)
return 0;
if (!asn1_uint_decode(ctx, end, &request->error_status))
return 0;
if (!asn1_header_decode(ctx, &end, &cls, &con, &tag))
return 0;
if (cls != ASN1_UNI || con != ASN1_PRI || tag != ASN1_INT)
return 0;
if (!asn1_uint_decode(ctx, end, &request->error_index))
return 0;
return 1;
}
/*
* Fast checksum update for possibly oddly-aligned UDP byte, from the
* code example in the draft.
*/
static void fast_csum(__sum16 *csum,
const unsigned char *optr,
const unsigned char *nptr,
int offset)
{
unsigned char s[4];
if (offset & 1) {
s[0] = ~0;
s[1] = ~*optr;
s[2] = 0;
s[3] = *nptr;
} else {
s[0] = ~*optr;
s[1] = ~0;
s[2] = *nptr;
s[3] = 0;
}
*csum = csum_fold(csum_partial(s, 4, ~csum_unfold(*csum)));
}
/*
* Mangle IP address.
* - begin points to the start of the snmp messgae
* - addr points to the start of the address
*/
static inline void mangle_address(unsigned char *begin,
unsigned char *addr,
const struct oct1_map *map,
__sum16 *check)
{
if (map->from == NOCT1(addr)) {
u_int32_t old;
if (debug)
memcpy(&old, addr, sizeof(old));
*addr = map->to;
/* Update UDP checksum if being used */
if (*check) {
fast_csum(check,
&map->from, &map->to, addr - begin);
}
if (debug)
printk(KERN_DEBUG "bsalg: mapped %pI4 to %pI4\n",
&old, addr);
}
}
static unsigned char snmp_trap_decode(struct asn1_ctx *ctx,
struct snmp_v1_trap *trap,
const struct oct1_map *map,
__sum16 *check)
{
unsigned int cls, con, tag, len;
unsigned char *end;
if (!asn1_header_decode(ctx, &end, &cls, &con, &tag))
return 0;
if (cls != ASN1_UNI || con != ASN1_PRI || tag != ASN1_OJI)
return 0;
if (!asn1_oid_decode(ctx, end, &trap->id, &trap->id_len))
return 0;
if (!asn1_header_decode(ctx, &end, &cls, &con, &tag))
goto err_id_free;
if (!((cls == ASN1_APL && con == ASN1_PRI && tag == SNMP_IPA) ||
(cls == ASN1_UNI && con == ASN1_PRI && tag == ASN1_OTS)))
goto err_id_free;
if (!asn1_octets_decode(ctx, end, (unsigned char **)&trap->ip_address, &len))
goto err_id_free;
/* IPv4 only */
if (len != 4)
goto err_addr_free;
mangle_address(ctx->begin, ctx->pointer - 4, map, check);
if (!asn1_header_decode(ctx, &end, &cls, &con, &tag))
goto err_addr_free;
if (cls != ASN1_UNI || con != ASN1_PRI || tag != ASN1_INT)
goto err_addr_free;
if (!asn1_uint_decode(ctx, end, &trap->general))
goto err_addr_free;
if (!asn1_header_decode(ctx, &end, &cls, &con, &tag))
goto err_addr_free;
if (cls != ASN1_UNI || con != ASN1_PRI || tag != ASN1_INT)
goto err_addr_free;
if (!asn1_uint_decode(ctx, end, &trap->specific))
goto err_addr_free;
if (!asn1_header_decode(ctx, &end, &cls, &con, &tag))
goto err_addr_free;
if (!((cls == ASN1_APL && con == ASN1_PRI && tag == SNMP_TIT) ||
(cls == ASN1_UNI && con == ASN1_PRI && tag == ASN1_INT)))
goto err_addr_free;
if (!asn1_ulong_decode(ctx, end, &trap->time))
goto err_addr_free;
return 1;
err_addr_free:
kfree((unsigned long *)trap->ip_address);
err_id_free:
kfree(trap->id);
return 0;
}
/*****************************************************************************
*
* Misc. routines
*
*****************************************************************************/
static void hex_dump(const unsigned char *buf, size_t len)
{
size_t i;
for (i = 0; i < len; i++) {
if (i && !(i % 16))
printk("\n");
printk("%02x ", *(buf + i));
}
printk("\n");
}
/*
* Parse and mangle SNMP message according to mapping.
* (And this is the fucking 'basic' method).
*/
static int snmp_parse_mangle(unsigned char *msg,
u_int16_t len,
const struct oct1_map *map,
__sum16 *check)
{
unsigned char *eoc, *end;
unsigned int cls, con, tag, vers, pdutype;
struct asn1_ctx ctx;
struct asn1_octstr comm;
struct snmp_object *obj;
if (debug > 1)
hex_dump(msg, len);
asn1_open(&ctx, msg, len);
/*
* Start of SNMP message.
*/
if (!asn1_header_decode(&ctx, &eoc, &cls, &con, &tag))
return 0;
if (cls != ASN1_UNI || con != ASN1_CON || tag != ASN1_SEQ)
return 0;
/*
* Version 1 or 2 handled.
*/
if (!asn1_header_decode(&ctx, &end, &cls, &con, &tag))
return 0;
if (cls != ASN1_UNI || con != ASN1_PRI || tag != ASN1_INT)
return 0;
if (!asn1_uint_decode (&ctx, end, &vers))
return 0;
if (debug > 1)
printk(KERN_DEBUG "bsalg: snmp version: %u\n", vers + 1);
if (vers > 1)
return 1;
/*
* Community.
*/
if (!asn1_header_decode (&ctx, &end, &cls, &con, &tag))
return 0;
if (cls != ASN1_UNI || con != ASN1_PRI || tag != ASN1_OTS)
return 0;
if (!asn1_octets_decode(&ctx, end, &comm.data, &comm.len))
return 0;
if (debug > 1) {
unsigned int i;
printk(KERN_DEBUG "bsalg: community: ");
for (i = 0; i < comm.len; i++)
printk("%c", comm.data[i]);
printk("\n");
}
kfree(comm.data);
/*
* PDU type
*/
if (!asn1_header_decode(&ctx, &eoc, &cls, &con, &pdutype))
return 0;
if (cls != ASN1_CTX || con != ASN1_CON)
return 0;
if (debug > 1) {
static const unsigned char *const pdus[] = {
[SNMP_PDU_GET] = "get",
[SNMP_PDU_NEXT] = "get-next",
[SNMP_PDU_RESPONSE] = "response",
[SNMP_PDU_SET] = "set",
[SNMP_PDU_TRAP1] = "trapv1",
[SNMP_PDU_BULK] = "bulk",
[SNMP_PDU_INFORM] = "inform",
[SNMP_PDU_TRAP2] = "trapv2"
};
if (pdutype > SNMP_PDU_TRAP2)
printk(KERN_DEBUG "bsalg: bad pdu type %u\n", pdutype);
else
printk(KERN_DEBUG "bsalg: pdu: %s\n", pdus[pdutype]);
}
if (pdutype != SNMP_PDU_RESPONSE &&
pdutype != SNMP_PDU_TRAP1 && pdutype != SNMP_PDU_TRAP2)
return 1;
/*
* Request header or v1 trap
*/
if (pdutype == SNMP_PDU_TRAP1) {
struct snmp_v1_trap trap;
unsigned char ret = snmp_trap_decode(&ctx, &trap, map, check);
if (ret) {
kfree(trap.id);
kfree((unsigned long *)trap.ip_address);
} else
return ret;
} else {
struct snmp_request req;
if (!snmp_request_decode(&ctx, &req))
return 0;
if (debug > 1)
printk(KERN_DEBUG "bsalg: request: id=0x%lx error_status=%u "
"error_index=%u\n", req.id, req.error_status,
req.error_index);
}
/*
* Loop through objects, look for IP addresses to mangle.
*/
if (!asn1_header_decode(&ctx, &eoc, &cls, &con, &tag))
return 0;
if (cls != ASN1_UNI || con != ASN1_CON || tag != ASN1_SEQ)
return 0;
while (!asn1_eoc_decode(&ctx, eoc)) {
unsigned int i;
if (!snmp_object_decode(&ctx, &obj)) {
if (obj) {
kfree(obj->id);
kfree(obj);
}
return 0;
}
if (debug > 1) {
printk(KERN_DEBUG "bsalg: object: ");
for (i = 0; i < obj->id_len; i++) {
if (i > 0)
printk(".");
printk("%lu", obj->id[i]);
}
printk(": type=%u\n", obj->type);
}
if (obj->type == SNMP_IPADDR)
mangle_address(ctx.begin, ctx.pointer - 4, map, check);
kfree(obj->id);
kfree(obj);
}
if (!asn1_eoc_decode(&ctx, eoc))
return 0;
return 1;
}
/*****************************************************************************
*
* NAT routines.
*
*****************************************************************************/
/*
* SNMP translation routine.
*/
static int snmp_translate(struct nf_conn *ct,
enum ip_conntrack_info ctinfo,
struct sk_buff *skb)
{
struct iphdr *iph = ip_hdr(skb);
struct udphdr *udph = (struct udphdr *)((__be32 *)iph + iph->ihl);
u_int16_t udplen = ntohs(udph->len);
u_int16_t paylen = udplen - sizeof(struct udphdr);
int dir = CTINFO2DIR(ctinfo);
struct oct1_map map;
/*
* Determine mappping for application layer addresses based
* on NAT manipulations for the packet.
*/
if (dir == IP_CT_DIR_ORIGINAL) {
/* SNAT traps */
map.from = NOCT1(&ct->tuplehash[dir].tuple.src.u3.ip);
map.to = NOCT1(&ct->tuplehash[!dir].tuple.dst.u3.ip);
} else {
/* DNAT replies */
map.from = NOCT1(&ct->tuplehash[!dir].tuple.src.u3.ip);
map.to = NOCT1(&ct->tuplehash[dir].tuple.dst.u3.ip);
}
if (map.from == map.to)
return NF_ACCEPT;
if (!snmp_parse_mangle((unsigned char *)udph + sizeof(struct udphdr),
paylen, &map, &udph->check)) {
net_warn_ratelimited("bsalg: parser failed\n");
return NF_DROP;
}
return NF_ACCEPT;
}
/* We don't actually set up expectations, just adjust internal IP
* addresses if this is being NATted */
static int help(struct sk_buff *skb, unsigned int protoff,
struct nf_conn *ct,
enum ip_conntrack_info ctinfo)
{
int dir = CTINFO2DIR(ctinfo);
unsigned int ret;
const struct iphdr *iph = ip_hdr(skb);
const struct udphdr *udph = (struct udphdr *)((__be32 *)iph + iph->ihl);
/* SNMP replies and originating SNMP traps get mangled */
if (udph->source == htons(SNMP_PORT) && dir != IP_CT_DIR_REPLY)
return NF_ACCEPT;
if (udph->dest == htons(SNMP_TRAP_PORT) && dir != IP_CT_DIR_ORIGINAL)
return NF_ACCEPT;
/* No NAT? */
if (!(ct->status & IPS_NAT_MASK))
return NF_ACCEPT;
/*
* Make sure the packet length is ok. So far, we were only guaranteed
* to have a valid length IP header plus 8 bytes, which means we have
* enough room for a UDP header. Just verify the UDP length field so we
* can mess around with the payload.
*/
if (ntohs(udph->len) != skb->len - (iph->ihl << 2)) {
net_warn_ratelimited("SNMP: dropping malformed packet src=%pI4 dst=%pI4\n",
&iph->saddr, &iph->daddr);
return NF_DROP;
}
if (!skb_make_writable(skb, skb->len))
return NF_DROP;
spin_lock_bh(&snmp_lock);
ret = snmp_translate(ct, ctinfo, skb);
spin_unlock_bh(&snmp_lock);
return ret;
}
static const struct nf_conntrack_expect_policy snmp_exp_policy = {
.max_expected = 0,
.timeout = 180,
};
static struct nf_conntrack_helper snmp_helper __read_mostly = {
.me = THIS_MODULE,
.help = help,
.expect_policy = &snmp_exp_policy,
.name = "snmp",
.tuple.src.l3num = AF_INET,
.tuple.src.u.udp.port = cpu_to_be16(SNMP_PORT),
.tuple.dst.protonum = IPPROTO_UDP,
};
static struct nf_conntrack_helper snmp_trap_helper __read_mostly = {
.me = THIS_MODULE,
.help = help,
.expect_policy = &snmp_exp_policy,
.name = "snmp_trap",
.tuple.src.l3num = AF_INET,
.tuple.src.u.udp.port = cpu_to_be16(SNMP_TRAP_PORT),
.tuple.dst.protonum = IPPROTO_UDP,
};
/*****************************************************************************
*
* Module stuff.
*
*****************************************************************************/
static int __init nf_nat_snmp_basic_init(void)
{
int ret = 0;
BUG_ON(nf_nat_snmp_hook != NULL);
RCU_INIT_POINTER(nf_nat_snmp_hook, help);
ret = nf_conntrack_helper_register(&snmp_trap_helper);
if (ret < 0) {
nf_conntrack_helper_unregister(&snmp_helper);
return ret;
}
return ret;
}
static void __exit nf_nat_snmp_basic_fini(void)
{
RCU_INIT_POINTER(nf_nat_snmp_hook, NULL);
nf_conntrack_helper_unregister(&snmp_trap_helper);
}
module_init(nf_nat_snmp_basic_init);
module_exit(nf_nat_snmp_basic_fini);
module_param(debug, int, 0600);