[Patch net] netrom: hold sock when setting skb->destructor

[Patch net] netrom: hold sock when setting skb->destructor

[Cong Wang]

sock_efree() releases the sock refcnt, if we don't hold this refcnt
when setting skb->destructor to it, the refcnt would not be balanced.
This leads to several bug reports from syzbot.

I have checked other users of sock_efree(), all of them hold the
sock refcnt.

Fixes: c8c8218ec5af ("netrom: fix a memory leak in nr_rx_frame()")
Reported-and-tested-by: <syzbot+622bdabb128acc33427d@syzkaller.appspotmail.com>
Reported-and-tested-by: <syzbot+6eaef7158b19e3fec3a0@syzkaller.appspotmail.com>
Reported-and-tested-by: <syzbot+9399c158fcc09b21d0d2@syzkaller.appspotmail.com>
Reported-and-tested-by: <syzbot+a34e5f3d0300163f0c87@syzkaller.appspotmail.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
---
 net/netrom/af_netrom.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/net/netrom/af_netrom.c b/net/netrom/af_netrom.c
index 96740d389377..c4f54ad2b98a 100644
--- a/net/netrom/af_netrom.c
+++ b/net/netrom/af_netrom.c
@@ -967,6 +967,7 @@ int nr_rx_frame(struct sk_buff *skb, struct net_device *dev)
 
 	window = skb->data[20];
 
+	sock_hold(make);
 	skb->sk             = make;
 	skb->destructor     = sock_efree;
 	make->sk_state	    = TCP_ESTABLISHED;
-- 
2.21.0

Re: [Patch net] netrom: hold sock when setting skb->destructor

[David Miller]

From: Cong Wang <xiyou.wangcong@gmail.com>
Date: Mon, 22 Jul 2019 20:41:22 -0700

> sock_efree() releases the sock refcnt, if we don't hold this refcnt
> when setting skb->destructor to it, the refcnt would not be balanced.
> This leads to several bug reports from syzbot.
> 
> I have checked other users of sock_efree(), all of them hold the
> sock refcnt.
> 
> Fixes: c8c8218ec5af ("netrom: fix a memory leak in nr_rx_frame()")
> Reported-and-tested-by: <syzbot+622bdabb128acc33427d@syzkaller.appspotmail.com>
> Reported-and-tested-by: <syzbot+6eaef7158b19e3fec3a0@syzkaller.appspotmail.com>
> Reported-and-tested-by: <syzbot+9399c158fcc09b21d0d2@syzkaller.appspotmail.com>
> Reported-and-tested-by: <syzbot+a34e5f3d0300163f0c87@syzkaller.appspotmail.com>
> Cc: Ralf Baechle <ralf@linux-mips.org>
> Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>

Applied and queued up for -stable.