Messages in this thread | | | Subject | Re: [PATCH] net: thunderx: prevent concurrent data re-writing by nicvf_set_rx_mode | From | Dean Nelson <> | Date | Mon, 11 Jun 2018 06:22:14 -0500 |
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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.
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