This is output from valgrind, pointing to a possible problem in
libnetfilter_log.c +307.
==16332== Syscall param socketcall.sendmsg(msg.msg_iov[i]) points to
uninitialised byte(s)
==16332== at 0x40E0316: sendmsg (socket.S:65)
==16332== by 0x42632AA: nflog_set_mode (libnetfilter_log.c:307)
==16332== by 0x424315B: start (ulogd_inppkt_NFLOG.c:466)
==16332== by 0x804C5E9: create_stack (ulogd.c:961)
==16332== by 0x804E85B: cfg_parser_action_plugin (cfg_parser.l:524)
==16332== by 0x805040F: cfg_parser (cfg_parser.l:590)
==16332== by 0x805061B: cfg_parser_parse_file (cfg_parser.l:773)
==16332== by 0x804D4B1: config_parse_file (conffile.c:260)
==16332== by 0x804B497: main (ulogd.c:1405)
==16332== Address 0xBE8B29F5 is on thread 1's stack
excerpt from libnetfilter_log.c:
int nflog_set_mode(struct nflog_g_handle *gh,
u_int8_t mode, u_int32_t range)
{
char buf[NFNL_HEADER_LEN
+NFA_LENGTH(sizeof(struct nfulnl_msg_config_mode))];
struct nfulnl_msg_config_mode params;
struct nlmsghdr *nmh = (struct nlmsghdr *) buf;
nfnl_fill_hdr(gh->h->nfnlssh, nmh, 0, AF_UNSPEC, gh->id,
NFULNL_MSG_CONFIG, NLM_F_REQUEST|NLM_F_ACK);
params.copy_range = htonl(range); /* copy_range is short */
params.copy_mode = mode;
nfnl_addattr_l(nmh, sizeof(buf), NFULA_CFG_MODE, ¶ms,
sizeof(params));
return nfnl_talk(gh->h->nfnlh, nmh, 0, 0, NULL, NULL, NULL);
}
The warning could not be suppressed by zeroing the message buffer in
nflog_setmode, but it could be suppressed by zeroing struct
nfulnl_msg_config_mode params:
excerpt from libnetfilter_log/linux_nfnetlink_log.h:
struct nfulnl_msg_config_mode {
u_int32_t copy_range;
u_int8_t copy_mode;
u_int8_t _pad;
} __attribute__ ((packed));
Therefore, this warning is caused by "_pad" remaining uninitialised.
Referencing "_pad" explicitely would be somewhat unpleasant. Using memset
would induce additional computation only to suppress a warning. Best solution
would be to extend .copy_mode from u_int8_t to u_int16_t and drop ._pad
completely. There are more issues like that in linux_nfnetlink_log.h. I
wonder why this approach was choosen to achieve 16-bit alignment: "_pad "
will be transmitted anyway.
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