Re: [PATCH] tg3: Avoid NULL pointer dereference in tg3_get_nstats()

On Thu, Jan 5, 2017 at 9:33 AM, David Miller [off-list ref] wrote:

From: Wang Yufen <redacted>
Date: Thu, 5 Jan 2017 22:13:21 +0800

quoted

From: Yufen Wang <redacted>

A possible NULL pointer dereference in tg3_get_stats64 while doing
tg3_free_consistent.

 ...

quoted

This patch avoids the NULL pointer dereference by using !tg3_flag(tp, INIT_COMPLETE)
instate of !tp->hw_stats.

Signed-off-by: Yufen Wang <redacted>
---
 drivers/net/ethernet/broadcom/tg3.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/broadcom/tg3.c b/drivers/net/ethernet/broadcom/tg3.c
index 185e9e0..012f18d 100644
--- a/drivers/net/ethernet/broadcom/tg3.c
+++ b/drivers/net/ethernet/broadcom/tg3.c

@@ -14148,7 +14148,7 @@ static struct rtnl_link_stats64 *tg3_get_stats64(struct net_device *dev,
      struct tg3 *tp = netdev_priv(dev);

      spin_lock_bh(&tp->lock);
-     if (!tp->hw_stats) {
+     if (!tg3_flag(tp, INIT_COMPLETE)) {

The real issue is the manner and order in which the driver performs
initialization actions relative to netif_device_{attach,detach}().

That is what needs to be fixed here, instead of adding more and more
ad-hoc tests to the various methods which can be invoked once the
netif_device_attach() occurs.

Normally, ndo_get_stats64() should be under rtnl lock in the netlink
code path and we should be safe. We only free tp->hw_stats under rtnl
lock in the close path or ethtool path.

But it looks like ndo_get_stats() can be called without rtnl lock from
net-procfs.c.  So it is possible that we'll read tp->hw_stats after it
has been freed.  For example, if we are reading /proc/net/dev and
closing tg3 at the same time.  David, is not taking rtnl_lock in
net-procfs.c by design?