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Message-ID: <tencent_FADDBB192B4F958DFF25E68DEF920F5D8507@qq.com>
Date: Wed, 7 Aug 2024 10:38:58 +0800
From: Edward Adam Davis <eadavis@...com>
To: syzbot+ad601904231505ad6617@...kaller.appspotmail.com
Cc: linux-kernel@...r.kernel.org,
syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [can?] WARNING: refcount bug in j1939_session_put
Fixes: c9c0ee5f20c5 ("net: skbuff: Skip early return in skb_unref when debugging")
Root cause: In commit c9c0ee5f20c5, There are following rules:
In debug builds (CONFIG_DEBUG_NET set), the reference count is always decremented, even when it's 1
This rule will cause the reference count to be 0 after calling skc_unref,
which will affect the release of skb.
#syz test: net-next 743ff02152bc
diff --git a/net/can/j1939/transport.c b/net/can/j1939/transport.c
index 4be73de5033c..257740076616 100644
--- a/net/can/j1939/transport.c
+++ b/net/can/j1939/transport.c
@@ -279,6 +279,9 @@ static void j1939_session_destroy(struct j1939_session *session)
while ((skb = skb_dequeue(&session->skb_queue)) != NULL) {
/* drop ref taken in j1939_session_skb_queue() */
skb_unref(skb);
+ if (IS_ENABLED(CONFIG_DEBUG_NET) &&
+ refcount_read(&skb->users) <= 0)
+ refcount_set(&skb->users, 1);
kfree_skb(skb);
}
__j1939_session_drop(session);
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