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net/sched: don't dereference a->goto_chain to read the chain index 

callers of tcf_gact_goto_chain_index() can potentially read an old value
of the chain index, or even dereference a NULL 'goto_chain' pointer,
because 'goto_chain' and 'tcfa_action' are read in the traffic path
without caring of concurrent write in the control path. The most recent
value of chain index can be read also from a->tcfa_action (it's encoded
there together with TC_ACT_GOTO_CHAIN bits), so we don't really need to
dereference 'goto_chain': just read the chain id from the control action.

Fixes: e457d86ada ("net: sched: add couple of goto_chain helpers")
Signed-off-by: Davide Caratti <dcaratti@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Davide Caratti 2019-03-20 15:00:15 +01:00 committed by David S. Miller
parent 7e0c8892df
commit fe384e2fa3
1 changed files with 1 additions and 1 deletions
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2
include/net/tc_act/tc_gact.h
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@ -56,7 +56,7 @@ static inline bool is_tcf_gact_goto_chain(const struct tc_action *a)
static inline u32 tcf_gact_goto_chain_index(const struct tc_action *a)
{
return a->goto_chain->index;
return READ_ONCE(a->tcfa_action) & TC_ACT_EXT_VAL_MASK;
}
#endif /* __NET_TC_GACT_H */