[PATCH 5.4 023/158] net: x25: Increase refcnt of "struct x25_neigh" in x25_rx_call_request

[Greg Kroah-Hartman]

From: Xie He <xie.he.0141@xxxxxxxxx>

[ Upstream commit 4ee18c179e5e815fa5575e0d2db0c05795a804ee ]

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@xxxxxxxxxx>
Signed-off-by: Xie He <xie.he.0141@xxxxxxxxx>
Link: https://lore.kernel.org/r/20201112103506.5875-1-xie.he.0141@xxxxxxxxx
Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 net/x25/af_x25.c |    1 +
 1 file changed, 1 insertion(+)

--- a/net/x25/af_x25.c
+++ b/net/x25/af_x25.c
@@ -1044,6 +1044,7 @@ int x25_rx_call_request(struct sk_buff *
 	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;