Hello,
I have a problem using snmpd from net-snmp 5.7.2 on HPUX (version 11.23 and
11.31, IA version).
When using UDP, the daemon doesn't send back correctly the reply. There is a
mistake in defining
the distant IP address : the snmpd daemon sends the replies to itself, the
distant IP address is always replaced with a local one.
I have had a look at the code : the problem comes from a wrong use of the
IP_RECVDSTADDR socket option.
Let me detail this :
Focussing on the send/receive functions using UDP protocol only (files
snmpUDPBaseDomain.c, snmpUDPDomain.c and snmpUDPIPv4BaseDomain.c), i can
summarize the ways used to send/receive packets to these lines :
- the use of recvmsg() and sendmsg() with the socket option IP_RECVDSTADDR,
- the use of recvmsg() and sendmsg() on linux with the socket option
IP_PKTINFO,
- for the others the use of recvfrom() and sendto() without any option.
By default, on HPUX we use the third one (the default "configure" settings).
The problem i described earlier is because the socket option IP_RECVDSTADDR is
defined in the
system files (in /usr/include/netinet/in.h). So we are by default using the
recvfrom()/sendto() with
the socket option IP_RECVDSTADDR. This last statment explains the problem i
have. The code doesn't
handle this mix.
The solution i found was to "comment" the lines :
snmpUDPIPv4BaseDomain.c (line 132) :
132 #elif defined(IP_RECVDSTADDR)
133 { /*
134 int sockopt = 1;
135 if (setsockopt(t->sock, IPPROTO_IP, IP_RECVDSTADDR,
&sockopt, sizeof sockopt) == -1) {
136 DEBUGMSGTL(("netsnmp_udp", "couldn't set
IP_RECVDSTADDR: %s\n",
137 strerror(errno)));
138 netsnmp_transport_free(t);
139 return NULL;
140 }
141 DEBUGMSGTL(("netsnmp_udp", "set IP_RECVDSTADDR\n"));
142 */ }
143 #endif
Now, i want to do it more properly. The question are How and Where ?
The choices are for me :
- add an #undef at the begining all three files or in the corresponding
header files ?
- change the "configure" step to handle this option,
- change the code from " #elif defined(IP_RECVDSTADDR)" to the test done
to enable the
use of this option in the sendmsg()/recvmsg() :
#if defined(IP_RECVDSTADDR) &&
HAVE_STRUCT_MSGHDR_MSG_CONTROL \
&& HAVE_STRUCT_MSGHDR_MSG_FLAGS
Due to the many uses of this option in the source code, the best way for me is
to "#undef" this
option globally for now. But the question stays : how ? I have tried the -U
CFLAGS without any success. .... Any ideas ?
Thanks in advance.
Regards,
JPV
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