On Sat, Sep 26, 2015 at 02:09:03PM -0400, Tejun Heo wrote:
>
> > @@ -1628,7 +1632,7 @@ static int netlink_getname(struct socket *sock,
> > struct sockaddr *addr,
> > nladdr->nl_pid = nlk->dst_portid;
> > nladdr->nl_groups = netlink_group_mask(nlk->dst_group);
> > } else {
> > - nladdr->nl_pid = nlk->portid;
> > + nladdr->nl_pid = netlink_bound(nlk) ? nlk->portid : 0;
> > nladdr->nl_groups = nlk->groups ? nlk->groups[0] : 0;
> > }
> > return 0;
>
> So, this is really weird because netlink_getname() doens't participate
> in the autobind race and thus it's perfectly fine for it to not worry
> about whether ->bound is set or the memory barrier - whoever its
> caller may be, the caller is of course responsible for ensuring that
> the port is bound and visible if it expects to read back the number -
> ie. if the caller doesn't know (in memory ordering sense) that
> bind/connect/sendmsg succeeded, it of course can't expect to reliably
> read back the port number. getname never needed the barrier. The
> above is shifting synchronization from the source to its users. This
> is a bad thing to do.
Thread 1 Thread 2
sendmsg getsockname
netlink_autobind netlink_getname
Thread 2 should not have to do anything special to guarantee that
getsockname does not return garbage. It must either be the bound
portid if the autobind completed in thread 1 and is visible or it
should return zero.
As it stands thread 2 may see a portid belonging to somebody else
if it catches the autobind in thread 1 trying different portids
while roving.
Cheers,
--
Email: Herbert Xu <herb...@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
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