Messages in this thread | | | Subject | Re: [RFC PATCH] tun: Don't put_page() for all negative return values from XDP program | From | Jason Wang <> | Date | Tue, 31 Mar 2020 10:59:01 +0800 |
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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
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