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net: dsa: Fix stale cpu_switch reference after unbind then bind 

Commit 9520ed8fb8 ("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: 9520ed8fb8 ("net: dsa: use cpu_switch instead of ds[0]")
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Reviewed-by: Vivien Didelot <vivien.didelot@savoirfairelinux.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
zero-colors
Florian Fainelli 2017-06-02 22:05:23 -07:00 committed by David S. Miller
parent e3e86b5119
commit b07ac98946
1 changed files with 3 additions and 1 deletions
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4
net/dsa/dsa2.c
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@ -484,8 +484,10 @@ static void dsa_dst_unapply(struct dsa_switch_tree *dst)
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;