Commit 0dcb8225 authored by Cong Wang's avatar Cong Wang Committed by David S. Miller

llc: use refcount_inc_not_zero() for llc_sap_find()

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: default avatarCong Wang <>
Signed-off-by: default avatarDavid S. Miller <>
parent 61ef4b07
...@@ -116,6 +116,11 @@ static inline void llc_sap_hold(struct llc_sap *sap) ...@@ -116,6 +116,11 @@ static inline void llc_sap_hold(struct llc_sap *sap)
refcount_inc(&sap->refcnt); 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); void llc_sap_close(struct llc_sap *sap);
static inline void llc_sap_put(struct llc_sap *sap) static inline void llc_sap_put(struct llc_sap *sap)
...@@ -73,8 +73,8 @@ struct llc_sap *llc_sap_find(unsigned char sap_value) ...@@ -73,8 +73,8 @@ struct llc_sap *llc_sap_find(unsigned char sap_value)
rcu_read_lock_bh(); rcu_read_lock_bh();
sap = __llc_sap_find(sap_value); sap = __llc_sap_find(sap_value);
if (sap) if (!sap || !llc_sap_hold_safe(sap))
llc_sap_hold(sap); sap = NULL;
rcu_read_unlock_bh(); rcu_read_unlock_bh();
return sap; return sap;
} }
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