* [PATCH] tun: Don't put_page() for all negative return values from XDP program
@ 2020-04-03 15:13 Will Deacon
2020-04-06 17:01 ` David Miller
0 siblings, 1 reply; 2+ messages in thread
From: Will Deacon @ 2020-04-03 15:13 UTC (permalink / raw)
To: netdev
Cc: linux-kernel, bpf, kernel-team, Will Deacon, David S. Miller,
Alexei Starovoitov, Daniel Borkmann, Eric Dumazet, Jason Wang
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>
---
RFC -> V1: Added Fixes tag and Jason's Ack.
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 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();
--
2.26.0.292.g33ef6b2f38-goog
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH] tun: Don't put_page() for all negative return values from XDP program
2020-04-03 15:13 [PATCH] tun: Don't put_page() for all negative return values from XDP program Will Deacon
@ 2020-04-06 17:01 ` David Miller
0 siblings, 0 replies; 2+ messages in thread
From: David Miller @ 2020-04-06 17:01 UTC (permalink / raw)
To: will
Cc: netdev, linux-kernel, bpf, kernel-team, ast, daniel, edumazet, jasowang
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.
^ permalink raw reply [flat|nested] 2+ messages in thread
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