From 222e05e0a29a4537575103a0e9118e385e928766 Mon Sep 17 00:00:00 2001 From: Cong Wang Date: Tue, 7 Aug 2018 12:41:38 -0700 Subject: [PATCH] llc: use refcount_inc_not_zero() for llc_sap_find() [ Upstream commit 0dcb82254d65f72333aa50ad626d1e9665ad093b ] llc_sap_put() decreases the refcnt before deleting sap from the global list. Therefore, there is a chance llc_sap_find() could find a sap with zero refcnt in this global list. Close this race condition by checking if refcnt is zero or not in llc_sap_find(), if it is zero then it is being removed so we can just treat it as gone. Reported-by: Signed-off-by: Cong Wang Signed-off-by: David S. Miller Signed-off-by: Greg Kroah-Hartman --- include/net/llc.h | 5 +++++ net/llc/llc_core.c | 4 ++-- 2 files changed, 7 insertions(+), 2 deletions(-) diff --git a/include/net/llc.h b/include/net/llc.h index dc35f25eb679..890a87318014 100644 --- a/include/net/llc.h +++ b/include/net/llc.h @@ -116,6 +116,11 @@ static inline void llc_sap_hold(struct llc_sap *sap) refcount_inc(&sap->refcnt); } +static inline bool llc_sap_hold_safe(struct llc_sap *sap) +{ + return refcount_inc_not_zero(&sap->refcnt); +} + void llc_sap_close(struct llc_sap *sap); static inline void llc_sap_put(struct llc_sap *sap) diff --git a/net/llc/llc_core.c b/net/llc/llc_core.c index 89041260784c..260b3dc1b4a2 100644 --- a/net/llc/llc_core.c +++ b/net/llc/llc_core.c @@ -73,8 +73,8 @@ struct llc_sap *llc_sap_find(unsigned char sap_value) rcu_read_lock_bh(); sap = __llc_sap_find(sap_value); - if (sap) - llc_sap_hold(sap); + if (!sap || !llc_sap_hold_safe(sap)) + sap = NULL; rcu_read_unlock_bh(); return sap; }