From: Davide Caratti <dcaratti@redhat.com>
Date: Wed, 20 Mar 2019 15:00:15 +0100
Subject: net/sched: don't dereference a->goto_chain to read the chain index
Patch-mainline: v5.1-rc3
Git-commit: fe384e2fa36ca084a456fd30558cccc75b4b3fbd
References: bsc#1064802 bsc#1066129

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>
Acked-by: Thomas Bogendoerfer <tbogendoerfer@suse.de>
---
 include/net/tc_act/tc_gact.h |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/include/net/tc_act/tc_gact.h
+++ b/include/net/tc_act/tc_gact.h
@@ -55,7 +55,7 @@ static inline bool is_tcf_gact_goto_chai
 
 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 */