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

[Gustavo A. R. Silva]

Quoting Leon Romanovsky <leon@xxxxxxxxxx>:

> 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.

I'm curious about why the return value of nlmsg_put is null checked  
118 out of 129 times (based on Coverity reports) in the last  
linux-next tree.

So based on what you mention, do you think all those checks are  
actually unnecessary and, maybe they should be removed?

Thanks
--
Gustavo