From: Oleksij Rempel <o.rempel@pengutronix.de>
To: mkl@pengutronix.de, "David S. Miller" <davem@davemloft.net>,
Jakub Kicinski <kuba@kernel.org>,
Oliver Hartkopp <socketcan@hartkopp.net>,
Robin van der Gracht <robin@protonic.nl>
Cc: Oleksij Rempel <o.rempel@pengutronix.de>,
Andre Naujoks <nautsch2@gmail.com>,
Eric Dumazet <edumazet@google.com>,
kernel@pengutronix.de, linux-can@vger.kernel.org,
netdev@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: [PATCH net v4 1/1] can: can_skb_set_owner(): fix ref counting if socket was closed before setting skb ownership
Date: Fri, 26 Feb 2021 10:24:56 +0100 [thread overview]
Message-ID: <20210226092456.27126-1-o.rempel@pengutronix.de> (raw)
There are two ref count variables controlling the free()ing of a socket:
- struct sock::sk_refcnt - which is changed by sock_hold()/sock_put()
- struct sock::sk_wmem_alloc - which accounts the memory allocated by
the skbs in the send path.
In case there are still TX skbs on the fly and the socket() is closed,
the struct sock::sk_refcnt reaches 0. In the TX-path the CAN stack
clones an "echo" skb, calls sock_hold() on the original socket and
references it. This produces the following back trace:
| WARNING: CPU: 0 PID: 280 at lib/refcount.c:25 refcount_warn_saturate+0x114/0x134
| refcount_t: addition on 0; use-after-free.
| Modules linked in: coda_vpu(E) v4l2_jpeg(E) videobuf2_vmalloc(E) imx_vdoa(E)
| CPU: 0 PID: 280 Comm: test_can.sh Tainted: G E 5.11.0-04577-gf8ff6603c617 #203
| Hardware name: Freescale i.MX6 Quad/DualLite (Device Tree)
| Backtrace:
| [<80bafea4>] (dump_backtrace) from [<80bb0280>] (show_stack+0x20/0x24) r7:00000000 r6:600f0113 r5:00000000 r4:81441220
| [<80bb0260>] (show_stack) from [<80bb593c>] (dump_stack+0xa0/0xc8)
| [<80bb589c>] (dump_stack) from [<8012b268>] (__warn+0xd4/0x114) r9:00000019 r8:80f4a8c2 r7:83e4150c r6:00000000 r5:00000009 r4:80528f90
| [<8012b194>] (__warn) from [<80bb09c4>] (warn_slowpath_fmt+0x88/0xc8) r9:83f26400 r8:80f4a8d1 r7:00000009 r6:80528f90 r5:00000019 r4:80f4a8c2
| [<80bb0940>] (warn_slowpath_fmt) from [<80528f90>] (refcount_warn_saturate+0x114/0x134) r8:00000000 r7:00000000 r6:82b44000 r5:834e5600 r4:83f4d540
| [<80528e7c>] (refcount_warn_saturate) from [<8079a4c8>] (__refcount_add.constprop.0+0x4c/0x50)
| [<8079a47c>] (__refcount_add.constprop.0) from [<8079a57c>] (can_put_echo_skb+0xb0/0x13c)
| [<8079a4cc>] (can_put_echo_skb) from [<8079ba98>] (flexcan_start_xmit+0x1c4/0x230) r9:00000010 r8:83f48610 r7:0fdc0000 r6:0c080000 r5:82b44000 r4:834e5600
| [<8079b8d4>] (flexcan_start_xmit) from [<80969078>] (netdev_start_xmit+0x44/0x70) r9:814c0ba0 r8:80c8790c r7:00000000 r6:834e5600 r5:82b44000 r4:82ab1f00
| [<80969034>] (netdev_start_xmit) from [<809725a4>] (dev_hard_start_xmit+0x19c/0x318) r9:814c0ba0 r8:00000000 r7:82ab1f00 r6:82b44000 r5:00000000 r4:834e5600
| [<80972408>] (dev_hard_start_xmit) from [<809c6584>] (sch_direct_xmit+0xcc/0x264) r10:834e5600 r9:00000000 r8:00000000 r7:82b44000 r6:82ab1f00 r5:834e5600 r4:83f27400
| [<809c64b8>] (sch_direct_xmit) from [<809c6c0c>] (__qdisc_run+0x4f0/0x534)
To fix this problem, only set skb ownership to sockets which have still
a ref count > 0.
Cc: Oliver Hartkopp <socketcan@hartkopp.net>
Cc: Andre Naujoks <nautsch2@gmail.com>
Suggested-by: Eric Dumazet <edumazet@google.com>
Fixes: 0ae89beb283a ("can: add destructor for self generated skbs")
Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
---
include/linux/can/skb.h | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)
diff --git a/include/linux/can/skb.h b/include/linux/can/skb.h
index 685f34cfba20..d82018cc0d0b 100644
--- a/include/linux/can/skb.h
+++ b/include/linux/can/skb.h
@@ -65,8 +65,12 @@ static inline void can_skb_reserve(struct sk_buff *skb)
static inline void can_skb_set_owner(struct sk_buff *skb, struct sock *sk)
{
- if (sk) {
- sock_hold(sk);
+ /*
+ * If the socket has already been closed by user space, the refcount may
+ * already be 0 (and the socket will be freed after the last TX skb has
+ * been freed). So only increase socket refcount if the refcount is > 0.
+ */
+ if (sk && refcount_inc_not_zero(&sk->sk_refcnt)) {
skb->destructor = sock_efree;
skb->sk = sk;
}
--
2.29.2
next reply other threads:[~2021-02-26 9:28 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-26 9:24 Oleksij Rempel [this message]
2021-02-26 17:15 ` [PATCH net v4 1/1] can: can_skb_set_owner(): fix ref counting if socket was closed before setting skb ownership Oliver Hartkopp
2021-03-01 10:56 ` Joakim Zhang
2021-03-02 2:21 ` Joakim Zhang
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