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

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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>
This commit is contained in:
Al Viro 2014-12-12 23:02:36 -05:00
parent 4c72c53be5
commit a8866ff6a5
1 changed files with 5 additions and 0 deletions
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5
net/netlink/af_netlink.c
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@ -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);