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SITNL: document interface and code of sitnl_send function

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Past changes make it clear that the interface was not well
understood.

While here, clean up the code to make it easier to understand.

Signed-off-by: Frank Lichtenheld <frank@lichtenheld.com>
This commit is contained in:
Frank Lichtenheld 2023-10-30 14:19:16 +01:00 committed by David Sommerseth
parent 1e135e4f05
commit 3b945e62e6
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GPG Key ID: 86CF944C9671FDF2
1 changed files with 53 additions and 43 deletions
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96
openvpn/tun/linux/client/sitnl.hpp
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@ -207,18 +207,37 @@ class SITNL
/**
* Send Netlink message and run callback on reply (if specified)
*
* If cb is not set, will request an ack message with NLM_F_ACK.
* Will return the value of error attribute of the ack message unless
* any other error occured during send or receive. Only NLMSG_ERROR and
* NLMSG_DONE messages are expected and handled without a callback function.
*
* If any other messages will be returned, a callback should be used. The
* callback will called on every message header except NLMSG_DONE (which ends
* the processing immediately). NLMSG_ERROR message is treated special in that
* if the callback returns a negative result on a NLMSG_ERROR message, the
* processing ends and that result is returned immediately. Otherwise, the
* function returns the return value of the callback called on the last message
* before NLMSG_DONE.
*
* @param payload nlmsghdr to embed into a nlmsg and send
* @param peer nladdr.nl_pid to use, can be 0
* @param groups nladdr.nl_groups to use, can be 0
* @param cb callback to call on returned nlmsghdrs, can be NULL
* @param arg_cb data argument for cb, can be NULL
* @return If any error occurs, negative errno. If cb is set, return value of last cb call, if not then value of error attribute in NLMSG_ERROR.
*/
static ssize_t
sitnl_send(struct nlmsghdr *payload, pid_t peer, unsigned int groups, sitnl_parse_reply_cb cb, void *arg_cb)
{
int len, fd;
ssize_t ret, rem_len, rcv_len;
ssize_t ret = 0;
const size_t buf_len = 16 * 1024;
struct sockaddr_nl nladdr = {};
struct nlmsgerr *err;
struct nlmsghdr *h;
unsigned int seq;
void *buf = NULL;
struct sockaddr_nl nladdr = {
.nl_family = AF_NETLINK,
.nl_pid = static_cast<__u32>(peer),
.nl_groups = groups,
};
struct iovec iov = {
.iov_base = payload,
.iov_len = payload->nlmsg_len,
@ -230,35 +249,31 @@ class SITNL
.msg_iovlen = 1,
};
nladdr.nl_family = AF_NETLINK;
nladdr.nl_pid = peer;
nladdr.nl_groups = groups;
payload->nlmsg_seq = static_cast<__u32>(time(NULL));
payload->nlmsg_seq = seq = static_cast<__u32>(time(NULL));
/* no need to send reply */
/* request ACK if no cb is used */
if (!cb)
{
payload->nlmsg_flags |= NLM_F_ACK;
}
fd = sitnl_socket();
/* resources that need cleaning on out */
void *buf = NULL;
int fd = sitnl_socket();
if (fd < 0)
{
OPENVPN_LOG(__func__ << ": can't open rtnl socket");
return -errno;
}
ret = sitnl_bind(fd, 0);
if (ret < 0)
if (sitnl_bind(fd, 0) < 0)
{
OPENVPN_LOG(__func__ << ": can't bind rtnl socket");
ret = -errno;
goto out;
}
ret = sendmsg(fd, &nlmsg, 0);
if (ret < 0)
if (sendmsg(fd, &nlmsg, 0) < 0)
{
OPENVPN_LOG(__func__ << ": rtnl: error on sendmsg()");
ret = -errno;
@ -283,7 +298,7 @@ class SITNL
*/
OPENVPN_LOG_RTNL(__func__ << ": checking for received messages");
iov.iov_len = buf_len;
rcv_len = recvmsg(fd, &nlmsg, 0);
ssize_t rcv_len = recvmsg(fd, &nlmsg, 0);
OPENVPN_LOG_RTNL(__func__ << ": rtnl: received " << rcv_len << " bytes");
if (rcv_len < 0)
{
@ -313,13 +328,13 @@ class SITNL
goto out;
}
h = (struct nlmsghdr *)buf;
while (rcv_len >= (int)sizeof(*h))
struct nlmsghdr *h = (struct nlmsghdr *)buf;
while (rcv_len >= static_cast<ssize_t>(sizeof(*h)))
{
len = h->nlmsg_len;
rem_len = len - sizeof(*h);
const auto len = h->nlmsg_len;
const auto data_len = len - sizeof(*h);
if ((rem_len < 0) || (len > rcv_len))
if ((sizeof(*h) > len) || (len > rcv_len))
{
if (nlmsg.msg_flags & MSG_TRUNC)
{
@ -339,31 +354,26 @@ class SITNL
if (h->nlmsg_type == NLMSG_ERROR)
{
err = (struct nlmsgerr *)NLMSG_DATA(h);
if (rem_len < (int)sizeof(struct nlmsgerr))
if (data_len < sizeof(struct nlmsgerr))
{
OPENVPN_LOG(__func__ << ": ERROR truncated");
ret = -EIO;
goto out;
}
struct nlmsgerr *err = (struct nlmsgerr *)NLMSG_DATA(h);
if (!err->error)
{
ret = 0;
if (cb)
ret = cb(h, arg_cb);
}
else
{
if (!err->error)
{
ret = 0;
if (cb)
{
ret = cb(h, arg_cb);
if (ret < 0)
goto out;
}
}
else
{
OPENVPN_LOG(__func__ << ": rtnl: generic error: "
<< strerror(-err->error)
<< " (" << err->error << ")");
ret = err->error;
}
OPENVPN_LOG(__func__ << ": rtnl: generic error: "
<< strerror(-err->error)
<< " (" << err->error << ")");
ret = err->error;
}
goto out;
}