@@ -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();
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: 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(-)