[PATCH AUTOSEL 4.14 23/43] net/sched: don't dereference a->goto_chain to read the chain index

Sasha Levin
2019-04-22T19:58:36Z

From: Davide Caratti <dcaratti@redhat.com>

[ 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@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin (Microsoft) <sashal@kernel.org>
---
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 e82d93346b63..bb74ea83d57d 100644
--- a/include/net/tc_act/tc_gact.h
+++ b/include/net/tc_act/tc_gact.h
@@ -51,7 +51,7 @@ 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 */
--
2.19.1