Message ID | 20200403151321.20166-1-will@kernel.org |
---|---|
State | Accepted |
Delegated to: | David Miller |
Headers | show |
Series | tun: Don't put_page() for all negative return values from XDP program | expand |
From: Will Deacon <will@kernel.org> Date: Fri, 3 Apr 2020 16:13:21 +0100 > 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 > > Cc: "David S. Miller" <davem@davemloft.net> > Cc: Alexei Starovoitov <ast@kernel.org> > Cc: Daniel Borkmann <daniel@iogearbox.net> > CC: Eric Dumazet <edumazet@google.com> > Acked-by: Jason Wang <jasowang@redhat.com> > Fixes: 8ae1aff0b331 ("tuntap: split out XDP logic") > Signed-off-by: Will Deacon <will@kernel.org> Applied and queued up for -stable, thank you.
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();