From: Will Deacon <will@kernel.org>
Date: Fri, 3 Apr 2020 16:13:21 +0100
Subject: tun: Don't put_page() for all negative return values from XDP program
Patch-mainline: v5.7-rc1
Git-commit: bee348907d19d654e8524d3a946dcd25b693aa7e
References: bsc#1109837
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>
Signed-off-by: David S. Miller <davem@davemloft.net>
Acked-by: Thomas Bogendoerfer <tbogendoerfer@suse.de>
---
drivers/net/tun.c | 10 ++++++----
1 file changed, 6 insertions(+), 4 deletions(-)
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -1697,8 +1697,12 @@ static struct sk_buff *tun_build_skb(str
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)
@@ -1712,8 +1716,6 @@ static struct sk_buff *tun_build_skb(str
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();