tuntap: fix use after free during release

BugLink: https://bugs.launchpad.net/bugs/1836117
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@virtuozzo.com>
Acked-by: Andrei Vagin <avagin@virtuozzo.com>
Fixes: b196d88aba8a ("tun: fix use after free for ptr_ring")
Signed-off-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Zubin Mithra <zsm@chromium.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
(cherry picked from commit 2a522aef03a4e11d6fdc05a107a023943b103e39)
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index e5bf7d1e3540d72f334082d56f99cc465db9b4ae..3ced0f259304be0450d8ff35d48d681478ec84e7 100644 (file)
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -657,6 +657,7 @@ static void __tun_detach(struct tun_file *tfile, bool clean)
                            tun->dev->reg_state == NETREG_REGISTERED)
                                unregister_netdevice(tun->dev);
                }
+               skb_array_cleanup(&tfile->tx_array);
                sock_put(&tfile->sk);
        }
 }
@@ -2894,7 +2895,6 @@ static int tun_chr_close(struct inode *inode, struct file *file)
        struct tun_file *tfile = file->private_data;
 
        tun_detach(tfile, true);
-       skb_array_cleanup(&tfile->tx_array);
 
        return 0;
 }