On Fri, 14 Jun 2019 13:04:53 +0200
Toke Høiland-Jørgensen <toke@xxxxxxxxxx> wrote:
> Toshiaki Makita <toshiaki.makita1@xxxxxxxxx> writes:
>
> > dev_map_free() waits for flush_needed bitmap to be empty in order to
> > ensure all flush operations have completed before freeing its entries.
> > However the corresponding clear_bit() was called before using the
> > entries, so the entries could be used after free.
> >
> > All access to the entries needs to be done before clearing the bit.
> > It seems commit a5e2da6e9787 ("bpf: netdev is never null in
> > __dev_map_flush") accidentally changed the clear_bit() and memory access
> > order.
> >
> > Note that the problem happens only in __dev_map_flush(), not in
> > dev_map_flush_old(). dev_map_flush_old() is called only after nulling
> > out the corresponding netdev_map entry, so dev_map_free() never frees
> > the entry thus no such race happens there.
> >
> > Fixes: a5e2da6e9787 ("bpf: netdev is never null in __dev_map_flush")
> > Signed-off-by: Toshiaki Makita <toshiaki.makita1@xxxxxxxxx>
>
> I recently posted a patch[0] that gets rid of the bitmap entirely, so I
> think you can drop this one...
One could argue that this is a stable tree fix... which unfortunately
will cause some pain for your patch. Or maybe for the maintainers, as
this is for 'bpf' git-tree and your patch is for 'bpf-next' git-tree.
> [0] https://lore.kernel.org/netdev/156042464148.25684.11881534392137955942.stgit@alrua-x1/
--
Best regards,
Jesper Dangaard Brouer
MSc.CS, Principal Kernel Engineer at Red Hat
LinkedIn: http://www.linkedin.com/in/brouer
