lkml.org 
[lkml]   [2020]   [Mar]   [30]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [RFC PATCH] tun: Don't put_page() for all negative return values from XDP program
From
Date

On 2020/3/31 上午12:12, Will Deacon wrote:
> When an XDP program is installed, tun_build_skb() grabs a reference to
> the current page fragment page if the program returns XDP_REDIRECT or
> XDP_TX. However, since tun_xdp_act() passes through negative return
> values from the XDP program, it is possible to trigger the error path by
> mistake and accidentally drop a reference to the fragments page without
> taking one, leading to a spurious free. This is believed to be the cause
> of some KASAN use-after-free reports from syzbot [1], although without a
> reproducer it is not possible to confirm whether this patch fixes the
> problem.
>
> Ensure that we only drop a reference to the fragments page if the XDP
> transmit or redirect operations actually fail.
>
> [1] https://syzkaller.appspot.com/bug?id=e76a6af1be4acd727ff6bbca669833f98cbf5d95


I think the patch fixes the issue reported. Since I can see the warn of
bad page state in put_page().


>
> Cc: "David S. Miller" <davem@davemloft.net>
> Cc: Alexei Starovoitov <ast@kernel.org>
> Cc: Daniel Borkmann <daniel@iogearbox.net>
> Cc: Jason Wang <jasowang@redhat.com>
> CC: Eric Dumazet <edumazet@google.com>
> Signed-off-by: Will Deacon <will@kernel.org>
> ---
>
> Sending as RFC because I've not been able to confirm that this fixes anything.
>
> drivers/net/tun.c | 10 ++++++----
> 1 file changed, 6 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/net/tun.c b/drivers/net/tun.c
> index 650c937ed56b..9de9b7d8aedd 100644
> --- a/drivers/net/tun.c
> +++ b/drivers/net/tun.c
> @@ -1715,8 +1715,12 @@ static struct sk_buff *tun_build_skb(struct tun_struct *tun,
> alloc_frag->offset += buflen;
> }
> err = tun_xdp_act(tun, xdp_prog, &xdp, act);
> - if (err < 0)
> - goto err_xdp;
> + if (err < 0) {
> + if (act == XDP_REDIRECT || act == XDP_TX)
> + put_page(alloc_frag->page);
> + goto out;
> + }
> +
> if (err == XDP_REDIRECT)
> xdp_do_flush();
> if (err != XDP_PASS)
> @@ -1730,8 +1734,6 @@ static struct sk_buff *tun_build_skb(struct tun_struct *tun,
>
> return __tun_build_skb(tfile, alloc_frag, buf, buflen, len, pad);
>
> -err_xdp:
> - put_page(alloc_frag->page);
> out:
> rcu_read_unlock();
> local_bh_enable();


Acked-by: Jason Wang <jasowang@redhat.com>

Thanks


\
 
 \ /
  Last update: 2020-03-31 04:59    [W:0.044 / U:8.332 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site