netdev - Re: [PATCH rdma-next 06/12] RDMA/uverbs: Don't overwrite NULL pointer with ZERO_SIZE

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Message-ID: <20180624195751.GM19151@ziepe.ca>
Date:   Sun, 24 Jun 2018 13:57:51 -0600
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Leon Romanovsky <leon@...nel.org>
Cc:     Doug Ledford <dledford@...hat.com>,
        Leon Romanovsky <leonro@...lanox.com>,
        RDMA mailing list <linux-rdma@...r.kernel.org>,
        Hadar Hen Zion <hadarh@...lanox.com>,
        Matan Barak <matanb@...lanox.com>,
        Michael J Ruhl <michael.j.ruhl@...el.com>,
        Noa Osherovich <noaos@...lanox.com>,
        Raed Salem <raeds@...lanox.com>,
        Yishai Hadas <yishaih@...lanox.com>,
        Saeed Mahameed <saeedm@...lanox.com>,
        linux-netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH rdma-next 06/12] RDMA/uverbs: Don't overwrite NULL
 pointer with ZERO_SIZE_PTR

On Sun, Jun 24, 2018 at 11:23:47AM +0300, Leon Romanovsky wrote:
> From: Leon Romanovsky <leonro@...lanox.com>
> 
> Number of specs is provided by user and in valid case can be equal to zero.
> Such argument causes to call to kcalloc() with zero-length request and in
> return the ZERO_SIZE_PTR is assigned. This pointer is different from NULL
> and makes various if (..) checks to success.

The one seems really weird. There is nothing wrong with ZERO_SIZE_PTR,
but this description and fix suggest that something did

ptr = kalloc(0);
ptr[0] = ...;

Which is not allowed of course. Doesn't this mean there is also a
missing range check someplace?

Jason