[ net-snmp-Bugs-3428506 ] netsnmp_gethostbyaddr() broken (called inconsistently)

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Bugs item #3428506, was opened at 2011-10-26 04:12
Message generated for change (Comment added) made by bvassche
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Category: library
Group: None
Status: Open
Resolution: None
Priority: 5
Private: No
Submitted By: Dan Lukes (dlukes)
Assigned to: Nobody/Anonymous (nobody)
Summary: netsnmp_gethostbyaddr() broken (called inconsistently)

Initial Comment:
netsnmp_gethostbyaddr() in snmplib/system.c is broken, so functions that depend on it (for example %A and %B formats of snmptrapd) doesn't work.

Following fragment is copied from git (HEAD):

  ------------------------------
 928 struct hostent *
 929 netsnmp_gethostbyaddr(const void *addr, socklen_t len, int type)
 930 {
...
 933     struct sockaddr_in *saddr_in =
 934         NETSNMP_REMOVE_CONST(struct sockaddr_in *,addr);
 935 
 936     DEBUGMSGTL(("dns:gethostbyaddr", "resolving { AF_INET, %s:%hu }\n",
 937                 inet_ntoa(saddr_in->sin_addr), ntohs(saddr_in->sin_port)));
...
 959     hp = gethostbyaddr((const void*) &saddr_in->sin_addr,
 960                        sizeof(struct in_addr), AF_INET);
  ------------------------------

A: The AF_INET case:
====================

The netsnmp_gethostbyaddr() is called with addr of type (struct in_addr), len=sizeof(struct in_addr) and type = AF_INET:

./apps/snmpnetstat/route.c:             hp = netsnmp_gethostbyaddr((char *)&in, sizeof (struct in_addr),
./apps/snmpnetstat/inet.c:                      hp = netsnmp_gethostbyaddr((char *)inp, sizeof (*inp),
./apps/snmptrapd_log.c:            host = netsnmp_gethostbyaddr((char *) pdu->agent_addr, 4, AF_INET);
./apps/snmptrapd_log.c:        host = netsnmp_gethostbyaddr((char *) pdu->agent_addr, 4, AF_INET);
./agent/mibgroup/disman/nslookup/lookupCtlTable.c:        lookup = netsnmp_gethostbyaddr(&addr_in, sizeof(addr_in), AF_INET);
./snmplib/transports/snmpIPv4BaseDomain.c:            host = netsnmp_gethostbyaddr((char *)&to->sin_addr, 4, AF_INET);

saddr_in variable is intialized incorrectly on line 933 - structures in_addr and sockaddr_in are not compatible (at least, they are not guaranteed to be compatible) so it's not possible to cast one of them to other. Resulting saddr_in->sin_addr_in does not contain value of addr. The gethostbyaddr on line 959 is called with uninitialized value and fail. The same is valid for val_gethostbyaddr() on 941

B: The AF_INET6 case:
====================
The netsnmp_gethostbyaddr() is called with addr of type (struct in_addr6), len=sizeof(struct in_addr6) and type = AF_INET6:

./agent/mibgroup/disman/nslookup/lookupCtlTable.c:        lookup = netsnmp_gethostbyaddr(&addr_in6, sizeof(addr_in6), AF_INET6);
./agent/mibgroup/disman/ping/pingCtlTable.c:        hp = netsnmp_gethostbyaddr((__u8 *) addr, sizeof(struct in6_addr),
./agent/mibgroup/disman/nslookup/lookupCtlTable.c:        lookup = netsnmp_gethostbyaddr(&addr_in6, sizeof(addr_in6), AF_INET6);
./apps/snmpnetstat/inet6.c:             hp = netsnmp_gethostbyaddr((const char *)in6p, sizeof(*in6p),

netsnmp_gethostbyaddr() is completelly broken in such case - it ignore supplied type and treat all calls as IPv4

 ========================================

We need either:

1. patch netsnmp_gethostbyaddr() to convert in_addr to sockaddr_in correctly and implement IPv6 handling
or
2. claim it obsolete, remove it and replace all calls to it by calls to netsnmp_getaddrinfo() 

My favourite is [2], but I'm not as familiar with net-snmp project as necesarry for such kind of decision


----------------------------------------------------------------------

>Comment By:  (bvassche)
Date: 2011-10-26 12:24

Message:
Does the attached (untested) patch help ?

----------------------------------------------------------------------

Comment By: Dan Lukes (dlukes)
Date: 2011-10-26 04:16

Message:
Oh well, missing version numbers. OKl, I analyzed it on FreeBSD
8.2-RELEASE, net-snmp 5.7

But code of netsnmp_gethostbyaddr() is the same in HEAD also 
OS (nor OS version) seems to be important information


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