| Message ID | 20180807194138.5863-1-xiyou.wangcong@gmail.com |
|---|---|
| State | Accepted, archived |
| Delegated to: | David Miller |
| Headers | show |
| Series | [net] llc: use refcount_inc_not_zero() for llc_sap_find() | expand |
From: Cong Wang <xiyou.wangcong@gmail.com> Date: Tue, 7 Aug 2018 12:41:38 -0700 > 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: <syzbot+278893f3f7803871f7ce@syzkaller.appspotmail.com> > Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com> Applied and queued up for -stable, thanks.
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; }
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: <syzbot+278893f3f7803871f7ce@syzkaller.appspotmail.com> Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com> --- include/net/llc.h | 5 +++++ net/llc/llc_core.c | 4 ++-- 2 files changed, 7 insertions(+), 2 deletions(-)