linux-kernel - [PATCH 4.11 013/150] net: dsa: Fix stale cpu_switch reference after unbind then bind

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Message-Id: <20170612152520.020106674@linuxfoundation.org>
Date:   Mon, 12 Jun 2017 17:23:40 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Florian Fainelli <f.fainelli@...il.com>,
        Vivien Didelot <vivien.didelot@...oirfairelinux.com>,
        "David S. Miller" <davem@...emloft.net>
Subject: [PATCH 4.11 013/150] net: dsa: Fix stale cpu_switch reference after unbind then bind

4.11-stable review patch.  If anyone has any objections, please let me know.

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

From: Florian Fainelli <f.fainelli@...il.com>

[ Upstream commit b07ac9894644202614ca87c69f3f45e424a82fef ]

Commit 9520ed8fb841 ("net: dsa: use cpu_switch instead of ds[0]")
replaced the use of dst->ds[0] with dst->cpu_switch since that is
functionally equivalent, however, we can now run into an use after free
scenario after unbinding then rebinding the switch driver.

The use after free happens because we do correctly initialize
dst->cpu_switch the first time we probe in dsa_cpu_parse(), then we
unbind the driver: dsa_dst_unapply() is called, and we rebind again.
dst->cpu_switch now points to a freed "ds" structure, and so when we
finally dereference it in dsa_cpu_port_ethtool_setup(), we oops.

To fix this, simply set dst->cpu_switch to NULL in dsa_dst_unapply()
which guarantees that we always correctly re-assign dst->cpu_switch in
dsa_cpu_parse().

Fixes: 9520ed8fb841 ("net: dsa: use cpu_switch instead of ds[0]")
Signed-off-by: Florian Fainelli <f.fainelli@...il.com>
Reviewed-by: Vivien Didelot <vivien.didelot@...oirfairelinux.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 net/dsa/dsa2.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/net/dsa/dsa2.c
+++ b/net/dsa/dsa2.c
@@ -440,8 +440,10 @@ static void dsa_dst_unapply(struct dsa_s
 		dsa_ds_unapply(dst, ds);
 	}

-	if (dst->cpu_switch)
+	if (dst->cpu_switch) {
 		dsa_cpu_port_ethtool_restore(dst->cpu_switch);
+		dst->cpu_switch = NULL;
+	}

 	pr_info("DSA: tree %d unapplied\n", dst->tree);
 	dst->applied = false;