[PATCH 4.19 42/72] net/sched: dont dereference a->goto_chain to read the chain index

From: Greg Kroah-Hartman
Date: Thu May 02 2019 - 11:27:30 EST

[ Upstream commit fe384e2fa36ca084a456fd30558cccc75b4b3fbd ]

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: e457d86ada27 ("net: sched: add couple of goto_chain helpers")
Signed-off-by: Davide Caratti <dcaratti@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Sasha Levin (Microsoft) <sashal@xxxxxxxxxx>
include/net/tc_act/tc_gact.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/net/tc_act/tc_gact.h b/include/net/tc_act/tc_gact.h
index ef8dd0db70ce..56935bf027a7 100644
--- a/include/net/tc_act/tc_gact.h
+++ b/include/net/tc_act/tc_gact.h
@@ -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 */