Re: [PATCH 1/1] NET: netpoll, fix potential NULL ptr dereference

[Jiri Slaby]

On 03/16/2010 06:12 PM, Matt Mackall wrote:
> I don't get it. The source of the branch tests for !ndev->npinfo and the
> original destination of the branch also tests for !ndev->npinfo. I don't
> see how it gets dereferenced.

Let's look at more of the context:
        if (!ndev->npinfo) {
                npinfo = kmalloc(sizeof(*npinfo), GFP_KERNEL);
                if (!npinfo) {         // npinfo is NULL
                        err = -ENOMEM;
                        goto release;
                }
...
release:                           // npinfo is still NULL
        if (!ndev->npinfo) {       // condition is the same (holds)
             // dereference below: vvvvvvvvvvvvvvv
                spin_lock_irqsave(&npinfo->rx_lock, flags);
                list_for_each_entry_safe(npe, tmp, &npinfo->rx_np, rx) {
                        npe->dev = NULL;
                }
                spin_unlock_irqrestore(&npinfo->rx_lock, flags);

                kfree(npinfo);
        }

thanks,
--
js
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