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authorCong Wang <xiyou.wangcong@gmail.com>2018-08-07 12:41:38 -0700
committerDavid S. Miller <davem@davemloft.net>2018-08-07 15:54:00 -0700
commit0dcb82254d65f72333aa50ad626d1e9665ad093b (patch)
tree0624bb5c365884b956d4abaf79d50e87a1406762
parent61ef4b07fcdc30535889990cf4229766502561cf (diff)
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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: <syzbot+278893f3f7803871f7ce@syzkaller.appspotmail.com> Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com> Signed-off-by: David S. Miller <davem@davemloft.net>
-rw-r--r--include/net/llc.h5
-rw-r--r--net/llc/llc_core.c4
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;
}