[PATCH net] gtp: serialize PDP deletion with link teardown

[Qing Ming <a0yami@mailbox.org>]

PDP contexts can be deleted through GTP_CMD_DELPDP or while the GTP
network device is being unregistered. The latter is serialized by RTNL,
but the generic-netlink delete path only holds RCU.

Running both paths concurrently can therefore make both paths delete the
same PDP context. On a KASAN-enabled kernel, a reproducer racing DELPDP
against RTM_DELLINK triggered:

  Oops: general protection fault, probably for non-canonical address
  KASAN: maybe wild-memory-access in range 
         [0xdead000000000120-0xdead000000000127]
  RIP: gtp_genl_del_pdp+0x1c1/0x420 [gtp]
  RBP: dead000000000122

The second deletion dereferenced the poisoned hlist pprev pointer.

Take RTNL around the DELPDP lookup and deletion so that PDP creation,
generic-netlink deletion and link teardown use the same serialization
domain.

Fixes: 459aa660eb1d ("gtp: add initial driver for datapath of GPRS Tunneling Protocol (GTP-U)")
Signed-off-by: Qing Ming <a0yami@mailbox.org>
---
 drivers/net/gtp.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/net/gtp.c b/drivers/net/gtp.c
index 427b91aca50d..7c4a99e2fd52 100644
--- a/drivers/net/gtp.c
+++ b/drivers/net/gtp.c
@@ -2127,6 +2127,8 @@ static int gtp_genl_del_pdp(struct sk_buff *skb, struct genl_info *info)
 	if (!info->attrs[GTPA_VERSION])
 		return -EINVAL;
 
+	rtnl_lock();
+
 	rcu_read_lock();
 
 	pctx = gtp_find_pdp(sock_net(skb->sk), info->attrs);
@@ -2147,6 +2149,7 @@ static int gtp_genl_del_pdp(struct sk_buff *skb, struct genl_info *info)
 
 out_unlock:
 	rcu_read_unlock();
+	rtnl_unlock();
 	return err;
 }
 
-- 
2.53.0