[snmpd] Fixed snmpd memory leak issue

[samaity]

Signed-off-by: Sangita Maity samaity@linkedin.com

Why I did it

This fixed memory leak in ETHERLIKE-MIB. The fix is not part of net-snmp(5.7.3 version). This PR includes the patch to fix memory leak issue.

ke->name in stdup-ed at line 297: n->name = strdup(RTA_DATA(tb[IFLA_IFNAME]));

How I did it

patched the fix.
[net-snmp] upstream fix link -> snmpd|upstream link

How to verify it

Before The fix

used valgrind to find memory leak.

root@lnos-x1-a-csw06:/# grep "definitely lost" valgrind-out.txt
==493== 4 bytes in 1 blocks are definitely lost in loss record 1 of 333
==493== 16 bytes in 1 blocks are definitely lost in loss record 25 of 333
==493== 757 bytes in 71 blocks are definitely lost in loss record 214 of 333
==493== 1,168 (32 direct, 1,136 indirect) bytes in 1 blocks are definitely lost in loss record 293 of 333
==493== 1,168 (32 direct, 1,136 indirect) bytes in 1 blocks are definitely lost in loss record 294 of 333
==493== 1,168 (32 direct, 1,136 indirect) bytes in 1 blocks are definitely lost in loss record 295 of 333
==493== 1,168 (32 direct, 1,136 indirect) bytes in 1 blocks are definitely lost in loss record 296 of 333
==493==    definitely lost: 905 bytes in 77 blocks

we can see the memory leak see in stack trace.
-> dot3stats_linux -> get_nlmsg -> strdup
https://github.com/net-snmp/net-snmp/blob/v5.7.3/agent/mibgroup/etherlike-mib/data_access/dot3stats_linux.c
https://github.com/net-snmp/net-snmp/blob/v5.7.3/agent/mibgroup/etherlike-mib/data_access/dot3stats_linux.c#L277

n = malloc(sizeof(*n));
    memset(n, 0, sizeof(*n));

    n->ifindex = ifi->ifi_index;
    n->name = strdup(RTA_DATA(tb[IFLA_IFNAME]));
    memcpy(&n->stats, RTA_DATA(tb[IFLA_STATS]), sizeof(n->stats));
    n->next = kern_db;
    kern_db = n;
    return 0;

we were not freeing space for EtherLike-MIB.AS interface mib queries were getting increased, we see memory increment.

        kern_db = ke->next;
        free(ke);

https://github.com/net-snmp/net-snmp/blob/v5.7.3/agent/mibgroup/etherlike-mib/data_access/dot3stats_linux.c#L467

==55== 757 bytes in 71 blocks are definitely lost in loss record 186 of 299
==55==    at 0x483577F: malloc (in /usr/lib/x86_64-linux-gnu/valgrind/vgpreload_memcheck-amd64-linux.so)
==55==    by 0x4EB6E49: strdup (strdup.c:42)
==55==    by 0x493F278: get_nlmsg (dot3stats_linux.c:299)
==55==    by 0x493F529: rtnl_dump_filter_l.constprop.3 (dot3stats_linux.c:370)
==55==    by 0x493FD7A: rtnl_dump_filter (dot3stats_linux.c:401)
==55==    by 0x493FD7A: _dot3Stats_netlink_get_errorcntrs (dot3stats_linux.c:424)
==55==    by 0x494009F: interface_dot3stats_get_errorcounters (dot3stats_linux.c:530)
==55==    by 0x48F6FDA: dot3StatsTable_container_load (dot3StatsTable_data_access.c:330)
==55==    by 0x485E76B: _cache_load (cache_handler.c:700)
==55==    by 0x485FA37: netsnmp_cache_helper_handler (cache_handler.c:638)
==55==    by 0x48720BC: netsnmp_call_handler (agent_handler.c:526)
==55==    by 0x48720BC: netsnmp_call_next_handler (agent_handler.c:640)
==55==    by 0x4865F75: table_helper_handler (table.c:717)
==55==    by 0x4871B66: netsnmp_call_handler (agent_handler.c:526)
==55==    by 0x4871B66: netsnmp_call_handlers (agent_handler.c:611)

757 bytes in 71 blocks are definitely lost in loss record 214 of 333
==493==    at 0x483577F: malloc (in /usr/lib/x86_64-linux-gnu/valgrind/vgpreload_memcheck-amd64-linux.so)
==493==    by 0x4EB6E49: strdup (strdup.c:42)
==493==    by 0x493F278: ??? (in /usr/lib/x86_64-linux-gnu/libnetsnmpmibs.so.30.0.3)
==493==    by 0x493F529: ??? (in /usr/lib/x86_64-linux-gnu/libnetsnmpmibs.so.30.0.3)
==493==    by 0x493FD7A: _dot3Stats_netlink_get_errorcntrs (in /usr/lib/x86_64-linux-gnu/libnetsnmpmibs.so.30.0.3)
==493==    by 0x494009F: interface_dot3stats_get_errorcounters (in /usr/lib/x86_64-linux-gnu/libnetsnmpmibs.so.30.0.3)
==493==    by 0x48F6FDA: dot3StatsTable_container_load (in /usr/lib/x86_64-linux-gnu/libnetsnmpmibs.so.30.0.3)
==493==    by 0x485E76B: _cache_load (cache_handler.c:700)
==493==    by 0x485FA37: netsnmp_cache_helper_handler (cache_handler.c:638)
==493==    by 0x48720BC: netsnmp_call_handler (agent_handler.c:526)
==493==    by 0x48720BC: netsnmp_call_next_handler (agent_handler.c:640)
==493==    by 0x4865F75: table_helper_handler (table.c:717)
==493==    by 0x4871B66: netsnmp_call_handler (agent_handler.c:526)
==493==    by 0x4871B66: netsnmp_call_handlers (agent_handler.c:611)

**After The fix**
no  memory leak in valgrind stack trace related to etherlike MIB.

[lguohan]

@samaity , we need backport to other branches as well.