Re: [PATCH] RDMA/nldev: Fix multiple potential NULL pointer dereferences

[Leon Romanovsky]

On Fri, Feb 09, 2018 at 07:36:49AM -0600, Gustavo A. R. Silva wrote:
> Hi Leon,
>
> Quoting Leon Romanovsky <leon@xxxxxxxxxx>:
>
> > On Fri, Feb 09, 2018 at 12:37:02AM -0600, Gustavo A. R. Silva wrote:
> > > In case the message header and payload cannot be stored, function
> > > nlmsg_put returns null.
> > >
> > > Fix this by adding multiple sanity checks and avoid a potential
> > > null dereference on _nlh_ when calling nlmsg_end.
> > >
> > > Addresses-Coverity-ID: 1454215 ("Dereference null return value")
> > > Addresses-Coverity-ID: 1454223 ("Dereference null return value")
> > > Addresses-Coverity-ID: 1454224 ("Dereference null return value")
> > > Addresses-Coverity-ID: 1464669 ("Dereference null return value")
> > > Addresses-Coverity-ID: 1464670 ("Dereference null return value")
> > > Addresses-Coverity-ID: 1464672 ("Dereference null return value")
> > > Fixes: e5c9469efcb1 ("RDMA/netlink: Add nldev device doit implementation")
> > > Fixes: c3f66f7b0052 ("RDMA/netlink: Implement nldev port doit callback")
> > > Fixes: 7d02f605f0dc ("RDMA/netlink: Add nldev port dumpit implementation")
> > > Fixes: b5fa635aab8f ("RDMA/nldev: Provide detailed QP information")
> > > Fixes: bf3c5a93c523 ("RDMA/nldev: Provide global resource utilization")
> > > Signed-off-by: Gustavo A. R. Silva <gustavo@xxxxxxxxxxxxxx>
> > > ---
> > >  drivers/infiniband/core/nldev.c | 26 +++++++++++++++++++++++++-
> > >  1 file changed, 25 insertions(+), 1 deletion(-)
> > >
> >
> > It will be much better to fix the tool instead of fixing ghost case.
> > This scenario is impossible for all those flows.
> > We can receive the skv/msg in two ways:
> >  * First by allocating new message with NLMSG_DEFAULT_SIZE, which has
> > more room
> >    than nlmsg_total_size(payload), payload is 0.
> >  * Second by getting from netlink.c and it will be at least "struct
> > nlmsghdr" too.
> >
> > Can you please add this info to the commit message?
> >
>
> Actually, I was planing to send a new version of this patch. This time using
> the unlikely macro for all the null checks on nlh.
>
> What do you think?

It is not datapath, so "unlikely" is not needed. Let's assume that smart enough
compiler will optimize such flow anyway, because nlmsg_put returns NULL
in unlikely scenario, so this check will be unlikely automatically too.

Thanks

>
> Thanks
> --
> Gustavo
>
>
>
>
>
>

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