On Sat, Sep 07, 2013 at 09:40:15PM +0200, Michio Honda wrote:
> Hi,
>
> Sorry for that I didn't respond to that warning.
> You are right, laddr == NULL && addrcnt == 1 is the indicator of the function called by
> asconf_mgmt().
>
> Since your patch is actually redundant, I would suggest putting comment on the
> line of "if ((laddr == NULL) && (addrcnt == 1)) {", and/or on the checking in your patch.
>
How can you guarantee its redundant, it seems possible to me to have an
association for which the laddr might not be found (the NULL case) while having
a multientry bind list, leading to a NULL dereference? I think we need the
check.
Or do you mean to indicate that checkout laddr == NULL & addrcnt == 1 is
actually redundant. If so, where is the redundant check?
Neil
> Cheers,
> - Michio
>
> On Sep 7, 2013, at 8:51 PM, Daniel Borkmann wrote:
>
> > This was originally reported in [1] and posted by Neil Horman [2], he said:
> >
> > Fix up a missed null pointer check in the asconf code. If we don't find
> > a local address, but we pass in an address length of more than 1, we may
> > dereference a NULL laddr pointer. Currently this can't happen, as the only
> > users of the function pass in the value 1 as the addrcnt parameter, but
> > its not hot path, and it doesn't hurt to check for NULL should that ever
> > be the case.
> >
> > The callpath from sctp_asconf_mgmt() looks okay. But this could be triggered
> > from sctp_setsockopt_bindx() call with SCTP_BINDX_REM_ADDR and addrcnt > 1
> > while passing all possible addresses from the bind list to SCTP_BINDX_REM_ADDR
> > so that we do *not* find a single address in the association's bind address
> > list that is not in the packed array of addresses. If this happens when we
> > have an established association with ASCONF-capable peers, then we could get
> > a NULL pointer dereference as we only check for laddr == NULL && addrcnt == 1
> > and call later sctp_make_asconf_update_ip() with NULL laddr.
> >
> > BUT: this actually won't happen as sctp_bindx_rem() will catch such a case
> > and return with an error earlier. As this is incredably unintuitive and error
> > prone, add a check to catch at least future bugs here. As Neil says, its not
> > hot path. Introduced by 8a07eb0a5 ("sctp: Add ASCONF operation on the
> > single-homed host").
> >
> > [1] http://www.spinics.net/lists/linux-sctp/msg02132.html
> > [2] http://www.spinics.net/lists/linux-sctp/msg02133.html
> >
> > Reported-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
> > Signed-off-by: Neil Horman <nhorman@xxxxxxxxxxxxx>
> > Signed-off-by: Daniel Borkmann <dborkman@xxxxxxxxxx>
> > Cc: Michio Honda <micchie@xxxxxxxxxxxxxx>
> > ---
> > net/sctp/socket.c | 3 +++
> > 1 file changed, 3 insertions(+)
> >
> > diff --git a/net/sctp/socket.c b/net/sctp/socket.c
> > index 5462bbb..911b71b 100644
> > --- a/net/sctp/socket.c
> > +++ b/net/sctp/socket.c
> > @@ -806,6 +806,9 @@ static int sctp_send_asconf_del_ip(struct sock *sk,
> > goto skip_mkasconf;
> > }
> >
> > + if (laddr == NULL)
> > + return -EINVAL;
> > +
> > /* We do not need RCU protection throughout this loop
> > * because this is done under a socket lock from the
> > * setsockopt call.
> > --
> > 1.7.11.7
> >
>
>
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