Commit a8866ff6 authored Dec 12, 2014 by Al Viro

netlink: make the check for "send from tx_ring" deterministic



As it is, zero msg_iovlen means that the first iovec in the kernel
array of iovecs is left uninitialized, so checking if its ->iov_base
is NULL is random.  Since the real users of that thing are doing
sendto(fd, NULL, 0, ...), they are getting msg_iovlen = 1 and
msg_iov[0] = {NULL, 0}, which is what this test is trying to catch.
As suggested by davem, let's just check that msg_iovlen was 1 and
msg_iov[0].iov_base was NULL - _that_ is well-defined and it catches
what we want to catch.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

parent 4c72c53b

net/netlink/af_netlink.c

+5 −0

Original line number	Diff line number	Diff line
		@@ -2298,7 +2298,12 @@ static int netlink_sendmsg(struct kiocb kiocb, struct socket sock,
		goto out;
		}

		/* It's a really convoluted way for userland to ask for mmaped
		* sendmsg(), but that's what we've got...
		*/
		if (netlink_tx_is_mmaped(sk) &&
		msg->msg_iter.type == ITER_IOVEC &&
		msg->msg_iter.nr_segs == 1 &&
		msg->msg_iter.iov->iov_base == NULL) {
		err = netlink_mmap_sendmsg(sk, msg, dst_portid, dst_group,
		&scm);

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