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SubjectRe: [PATCH net V2] tun: fix use after free for ptr_ring
On Fri, May 11, 2018 at 10:49:25AM +0800, Jason Wang wrote:
> We used to initialize ptr_ring during TUNSETIFF, this is because its
> size depends on the tx_queue_len of netdevice. And we try to clean it
> up when socket were detached from netdevice. A race were spotted when
> trying to do uninit during a read which will lead a use after free for
> pointer ring. Solving this by always initialize a zero size ptr_ring
> in open() and do resizing during TUNSETIFF, and then we can safely do
> cleanup during close(). With this, there's no need for the workaround
> that was introduced by commit 4df0bfc79904 ("tun: fix a memory leak
> for tfile->tx_array").
>
> Reported-by: syzbot+e8b902c3c3fadf0a9dba@syzkaller.appspotmail.com
> Cc: Eric Dumazet <eric.dumazet@gmail.com>
> Cc: Cong Wang <xiyou.wangcong@gmail.com>
> Cc: Michael S. Tsirkin <mst@redhat.com>
> Fixes: 1576d9860599 ("tun: switch to use skb array for tx")
> Signed-off-by: Jason Wang <jasowang@redhat.com>

Acked-by: Michael S. Tsirkin <mst@redhat.com>

and will you send the revert pls then?


> ---
> Changes from v1:
> - free ptr_ring during close()
> - use tun_ptr_free() during resie for safety
> ---
> drivers/net/tun.c | 27 ++++++++++++---------------
> 1 file changed, 12 insertions(+), 15 deletions(-)
>
> diff --git a/drivers/net/tun.c b/drivers/net/tun.c
> index ef33950..9fbbb32 100644
> --- a/drivers/net/tun.c
> +++ b/drivers/net/tun.c
> @@ -681,15 +681,6 @@ static void tun_queue_purge(struct tun_file *tfile)
> skb_queue_purge(&tfile->sk.sk_error_queue);
> }
>
> -static void tun_cleanup_tx_ring(struct tun_file *tfile)
> -{
> - if (tfile->tx_ring.queue) {
> - ptr_ring_cleanup(&tfile->tx_ring, tun_ptr_free);
> - xdp_rxq_info_unreg(&tfile->xdp_rxq);
> - memset(&tfile->tx_ring, 0, sizeof(tfile->tx_ring));
> - }
> -}
> -
> static void __tun_detach(struct tun_file *tfile, bool clean)
> {
> struct tun_file *ntfile;
> @@ -736,7 +727,8 @@ static void __tun_detach(struct tun_file *tfile, bool clean)
> tun->dev->reg_state == NETREG_REGISTERED)
> unregister_netdevice(tun->dev);
> }
> - tun_cleanup_tx_ring(tfile);
> + if (tun)
> + xdp_rxq_info_unreg(&tfile->xdp_rxq);
> sock_put(&tfile->sk);
> }
> }
> @@ -783,14 +775,14 @@ static void tun_detach_all(struct net_device *dev)
> tun_napi_del(tun, tfile);
> /* Drop read queue */
> tun_queue_purge(tfile);
> + xdp_rxq_info_unreg(&tfile->xdp_rxq);
> sock_put(&tfile->sk);
> - tun_cleanup_tx_ring(tfile);
> }
> list_for_each_entry_safe(tfile, tmp, &tun->disabled, next) {
> tun_enable_queue(tfile);
> tun_queue_purge(tfile);
> + xdp_rxq_info_unreg(&tfile->xdp_rxq);
> sock_put(&tfile->sk);
> - tun_cleanup_tx_ring(tfile);
> }
> BUG_ON(tun->numdisabled != 0);
>
> @@ -834,7 +826,8 @@ static int tun_attach(struct tun_struct *tun, struct file *file,
> }
>
> if (!tfile->detached &&
> - ptr_ring_init(&tfile->tx_ring, dev->tx_queue_len, GFP_KERNEL)) {
> + ptr_ring_resize(&tfile->tx_ring, dev->tx_queue_len,
> + GFP_KERNEL, tun_ptr_free)) {
> err = -ENOMEM;
> goto out;
> }
> @@ -3219,6 +3212,11 @@ static int tun_chr_open(struct inode *inode, struct file * file)
> &tun_proto, 0);
> if (!tfile)
> return -ENOMEM;
> + if (ptr_ring_init(&tfile->tx_ring, 0, GFP_KERNEL)) {
> + sk_free(&tfile->sk);
> + return -ENOMEM;
> + }
> +
> RCU_INIT_POINTER(tfile->tun, NULL);
> tfile->flags = 0;
> tfile->ifindex = 0;
> @@ -3239,8 +3237,6 @@ static int tun_chr_open(struct inode *inode, struct file * file)
>
> sock_set_flag(&tfile->sk, SOCK_ZEROCOPY);
>
> - memset(&tfile->tx_ring, 0, sizeof(tfile->tx_ring));
> -
> return 0;
> }
>
> @@ -3249,6 +3245,7 @@ static int tun_chr_close(struct inode *inode, struct file *file)
> struct tun_file *tfile = file->private_data;
>
> tun_detach(tfile, true);
> + ptr_ring_cleanup(&tfile->tx_ring, tun_ptr_free);
>
> return 0;
> }
> --
> 2.7.4

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