linux-kernel - [PATCH net v2] net: x25: Increase refcnt of "struct x25_neigh" in x25_rx_call

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Date:   Thu, 12 Nov 2020 02:35:06 -0800
From:   Xie He <xie.he.0141@...il.com>
To:     Jakub Kicinski <kuba@...nel.org>,
        "David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, Martin Schiller <ms@....tdt.de>
Cc:     Xie He <xie.he.0141@...il.com>
Subject: [PATCH net v2] net: x25: Increase refcnt of "struct x25_neigh" in x25_rx_call_request

The x25_disconnect function in x25_subr.c would decrease the refcount of
"x25->neighbour" (struct x25_neigh) and reset this pointer to NULL.

However, the x25_rx_call_request function in af_x25.c, which is called
when we receive a connection request, does not increase the refcount when
it assigns the pointer.

Fix this issue by increasing the refcount of "struct x25_neigh" in
x25_rx_call_request.

This patch fixes frequent kernel crashes when using AF_X25 sockets.

Fixes: 4becb7ee5b3d ("net/x25: Fix x25_neigh refcnt leak when x25 disconnect")
Cc: Martin Schiller <ms@....tdt.de>
Signed-off-by: Xie He <xie.he.0141@...il.com>
---
 net/x25/af_x25.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/net/x25/af_x25.c b/net/x25/af_x25.c
index 046d3fee66a9..a10487e7574c 100644
--- a/net/x25/af_x25.c
+++ b/net/x25/af_x25.c
@@ -1050,6 +1050,7 @@ int x25_rx_call_request(struct sk_buff *skb, struct x25_neigh *nb,
 	makex25->lci           = lci;
 	makex25->dest_addr     = dest_addr;
 	makex25->source_addr   = source_addr;
+	x25_neigh_hold(nb);
 	makex25->neighbour     = nb;
 	makex25->facilities    = facilities;
 	makex25->dte_facilities= dte_facilities;
-- 
2.27.0