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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Zumeng Chen <zumeng.chen@gmail.com>,
        Michael Chan <michael.chan@broadcom.com>,
        "David S. Miller" <davem@davemloft.net>
Subject: [PATCH 4.4 15/92] tg3: Fix vunmap() BUG_ON() triggered from tg3_free_consistent().
Date:   Thu, 24 May 2018 11:37:52 +0200
Message-Id: <20180524093200.638969190@linuxfoundation.org>
In-Reply-To: <20180524093159.286472249@linuxfoundation.org>
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4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Michael Chan <michael.chan@broadcom.com>

[ Upstream commit d89a2adb8bfe6f8949ff389acdb9fa298b6e8e12 ]

tg3_free_consistent() calls dma_free_coherent() to free tp->hw_stats
under spinlock and can trigger BUG_ON() in vunmap() because vunmap()
may sleep.  Fix it by removing the spinlock and relying on the
TG3_FLAG_INIT_COMPLETE flag to prevent race conditions between
tg3_get_stats64() and tg3_free_consistent().  TG3_FLAG_INIT_COMPLETE
is always cleared under tp->lock before tg3_free_consistent()
and therefore tg3_get_stats64() can safely access tp->hw_stats
under tp->lock if TG3_FLAG_INIT_COMPLETE is set.

Fixes: f5992b72ebe0 ("tg3: Fix race condition in tg3_get_stats64().")
Reported-by: Zumeng Chen <zumeng.chen@gmail.com>
Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/net/ethernet/broadcom/tg3.c |    9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

--- a/drivers/net/ethernet/broadcom/tg3.c
+++ b/drivers/net/ethernet/broadcom/tg3.c
@@ -8722,14 +8722,15 @@ static void tg3_free_consistent(struct t
 	tg3_mem_rx_release(tp);
 	tg3_mem_tx_release(tp);
 
-	/* Protect tg3_get_stats64() from reading freed tp->hw_stats. */
-	tg3_full_lock(tp, 0);
+	/* tp->hw_stats can be referenced safely:
+	 *     1. under rtnl_lock
+	 *     2. or under tp->lock if TG3_FLAG_INIT_COMPLETE is set.
+	 */
 	if (tp->hw_stats) {
 		dma_free_coherent(&tp->pdev->dev, sizeof(struct tg3_hw_stats),
 				  tp->hw_stats, tp->stats_mapping);
 		tp->hw_stats = NULL;
 	}
-	tg3_full_unlock(tp);
 }
 
 /*
@@ -14163,7 +14164,7 @@ static struct rtnl_link_stats64 *tg3_get
 	struct tg3 *tp = netdev_priv(dev);
 
 	spin_lock_bh(&tp->lock);
-	if (!tp->hw_stats) {
+	if (!tp->hw_stats || !tg3_flag(tp, INIT_COMPLETE)) {
 		*stats = tp->net_stats_prev;
 		spin_unlock_bh(&tp->lock);
 		return stats;