[PATCH 4.14 124/126] tuntap: fix use after free during release

[Greg Kroah-Hartman]

4.14-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Jason Wang <jasowang@xxxxxxxxxx>

commit 7063efd33bb15abc0160347f89eb5aba6b7d000e upstream.

After commit b196d88aba8a ("tun: fix use after free for ptr_ring") we
need clean up tx ring during release(). But unfortunately, it tries to
do the cleanup blindly after socket were destroyed which will lead
another use-after-free. Fix this by doing the cleanup before dropping
the last reference of the socket in __tun_detach().

Backport Note :-
Upstream commit moves the ptr_ring_cleanup call from tun_chr_close to
__tun_detach. Upstream applied that patch after replacing skb_array with
ptr_ring. This patch moves the skb_array_cleanup call from
tun_chr_close to __tun_detach.

Reported-by: Andrei Vagin <avagin@xxxxxxxxxxxxx>
Acked-by: Andrei Vagin <avagin@xxxxxxxxxxxxx>
Fixes: b196d88aba8a ("tun: fix use after free for ptr_ring")
Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Zubin Mithra <zsm@xxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 drivers/net/tun.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -575,6 +575,7 @@ static void __tun_detach(struct tun_file
 			    tun->dev->reg_state == NETREG_REGISTERED)
 				unregister_netdevice(tun->dev);
 		}
+		skb_array_cleanup(&tfile->tx_array);
 		sock_put(&tfile->sk);
 	}
 }
@@ -2646,7 +2647,6 @@ static int tun_chr_close(struct inode *i
 	struct tun_file *tfile = file->private_data;
 
 	tun_detach(tfile, true);
-	skb_array_cleanup(&tfile->tx_array);
 
 	return 0;
 }