Messages in this thread | | | Date | Tue, 12 Jun 2018 15:25:40 -0700 (PDT) | Subject | Re: [PATCH] net: thunderx: prevent concurrent data re-writing by nicvf_set_rx_mode | From | David Miller <> |
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From: Dean Nelson <dnelson@redhat.com> Date: Mon, 11 Jun 2018 06:22:14 -0500
> On 06/10/2018 02:35 PM, David Miller wrote: >> From: Vadim Lomovtsev <Vadim.Lomovtsev@caviumnetworks.com> >> Date: Fri, 8 Jun 2018 02:27:59 -0700 >> >>> + /* Save message data locally to prevent them from >>> + * being overwritten by next ndo_set_rx_mode call(). >>> + */ >>> + spin_lock(&nic->rx_mode_wq_lock); >>> + mode = vf_work->mode; >>> + mc = vf_work->mc; >>> + vf_work->mc = NULL; > > If I'm reading this code correctly, I believe nic->rx_mode_work.mc > will > have been set to NULL before the lock is dropped by > nicvf_set_rx_mode_task() and acquired by nicvf_set_rx_mode(). > > >>> + spin_unlock(&nic->rx_mode_wq_lock); >> At the moment you drop this lock, the memory behind 'mc' can be >> freed up by: >> >>> + spin_lock(&nic->rx_mode_wq_lock); >>> + kfree(nic->rx_mode_work.mc); > > So the kfree() will be called with a NULL pointer and quickly return. > > >> And you'll crash when you dereference it above via >> __nicvf_set_rx_mode_task(). >> > > I believe the call to kfree() in nicvf_set_rx_mode() is there to free > up a mc_list that has been allocated by nicvf_set_rx_mode() during a > previous callback to the function, one that has not yet been processed > by nicvf_set_rx_mode_task(). > > In this way only the last 'unprocessed' callback to > nicvf_set_rx_mode() > gets processed should there be multiple callbacks occurring between > the > times the nicvf_set_rx_mode_task() runs. > > In my testing with this patch, this is what I see happening.
You're right, my bad.
Patch applied.
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