From 0d322413d6cff0bd2ccafc03ab9314dc55417e9d Mon Sep 17 00:00:00 2001
From: Edward Cree <ecree@solarflare.com>
Date: Wed, 20 May 2015 11:10:03 +0100
Subject: [PATCH] sfc: protect filter table against use-after-free

If MCDI timeouts are encountered during efx_ef10_filter_table_remove(),
an FLR will be queued, but efx->filter_state will still be kfree()d.
The queued FLR will then call efx_ef10_filter_table_restore(), which
will try to use efx->filter_state. This previously caused a panic.
This patch adds an rwsem to protect the existence of efx->filter_state,
separately from the spinlock protecting its contents.  Users which can
race against efx_ef10_filter_table_remove() should down_read this rwsem.

Signed-off-by: Shradha Shah <sshah@solarflare.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
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