From: Will Deacon <will@xxxxxxxxxx> [ Upstream commit bee348907d19d654e8524d3a946dcd25b693aa7e ] 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@xxxxxxxxxxxxx> Cc: Alexei Starovoitov <ast@xxxxxxxxxx> Cc: Daniel Borkmann <daniel@xxxxxxxxxxxxx> CC: Eric Dumazet <edumazet@xxxxxxxxxx> Acked-by: Jason Wang <jasowang@xxxxxxxxxx> Fixes: 8ae1aff0b331 ("tuntap: split out XDP logic") Signed-off-by: Will Deacon <will@xxxxxxxxxx> Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> --- 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 69f553a028eee..16f5cb249ed59 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_map(); 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(); -- 2.20.1
