Messages in this thread | | | Date | Wed, 13 Jun 2018 02:15:39 -0700 | From | Vadim Lomovtsev <> | Subject | Re: [PATCH] net: thunderx: prevent concurrent data re-writing by nicvf_set_rx_mode |
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Sorry for delay.
On Tue, Jun 12, 2018 at 03:25:40PM -0700, David Miller wrote: > 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.
Thank you for your time.
WBR, Vadim
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