From: Will Deacon will@kernel.org
[ 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=e76a6af1be4acd727ff6bbca669833f98cbf5d9...
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 Signed-off-by: David S. Miller davem@davemloft.net Signed-off-by: Sasha Levin sashal@kernel.org --- 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 35e884a8242d9..6d3317d868d23 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();