Hi all,

I am using OpenWRT device with MUSL C library version 1.1.19 and I am running custom binary on it. I noticed that during testing my program started using 99% CPU.

I build OpenWRT myself so I have all the sources. I attached the gdbserver and checked what is going on.

What I found is that it executes this code:

static int netlink_msg_to_ifaddr(void *pctx, struct nlmsghdr *h)

{

struct ifaddrs_ctx *ctx = pctx;

struct ifaddrs_storage *ifs, *ifs0;

struct ifinfomsg *ifi = NLMSG_DATA(h);

struct ifaddrmsg *ifa = NLMSG_DATA(h);

struct rtattr *rta;

int stats_len = 0;

if (h->nlmsg_type == RTM_NEWLINK) {

for (rta = NLMSG_RTA(h, sizeof(*ifi)); NLMSG_RTAOK(rta, h); rta = RTA_NEXT(rta)) {

if (rta->rta_type != IFLA_STATS) continue;

stats_len = RTA_DATALEN(rta);

break;

}

} else {

for (ifs0 = ctx->hash[ifa->ifa_index % IFADDRS_HASH_SIZE]; ifs0; ifs0 = ifs0->hash_next)

if (ifs0->index == ifa->ifa_index)

break;

if (!ifs0) return 0;

}

From my GDB session:

(gdb) p *ctx

$10 = {first = 0xe1b0b0, last = 0xe1b1c0, hash = {0x0, 0xe1b0b0, 0xe1b1c0, 0x0 <repeats 61 times>}}

(gdb) p *h

$11 = {nlmsg_len = 1496, nlmsg_type = 16, nlmsg_flags = 2, nlmsg_seq = 1, nlmsg_pid = 3143810850}

(gdb) p *ifi

$12 = {ifi_family = 0 '\000', __ifi_pad = 0 '\000', ifi_type = 1, ifi_index = 3, ifi_flags = 69699, ifi_change = 0}

(gdb) p *ifa

$13 = {ifa_family = 0 '\000', ifa_prefixlen = 0 '\000', ifa_flags = 0 '\000', ifa_scope = 1 '\001', ifa_index = 3

(gdb) p *rta

$14 = {rta_len = 0, rta_type = 41}

As you can see the first message in netlink reply has a rta_len set to zero so the list is never traversed, only the first message is received every time.

I am not sure if this is the correct response from netlink, however the program is stucked here.

Any ideas?

Please CC me in reply.

Thanks and BR,

Matej