From: Al Viro Date: Sat, 13 Dec 2014 04:02:36 +0000 (-0500) Subject: netlink: make the check for "send from tx_ring" deterministic X-Git-Tag: v4.0-rc1~133^2~61^2~17 X-Git-Url: https://asedeno.scripts.mit.edu/gitweb/?a=commitdiff_plain;h=a8866ff6a5bce7d0ec465a63bc482a85c09b0d39;p=linux.git 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 --- diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c index a36777b7cfb6..4fd38a612ff6 100644 --- a/net/netlink/af_netlink.c +++ b/net/netlink/af_netlink.c @@ -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);