From 286228d382ba6320f04fa2e7c6fc8d4d92e428f4 Mon Sep 17 00:00:00 2001

From: Oleksij Rempel <o.rempel@pengutronix.de>

Date: Wed, 18 Dec 2019 09:39:02 +0100

Subject: [PATCH] can: can_create_echo_skb(): fix echo skb generation: always use skb_clone()

Git-commit: 286228d382ba6320f04fa2e7c6fc8d4d92e428f4

Patch-mainline: v5.10-rc3

References: git-fixes

All user space generated SKBs are owned by a socket (unless injected into the

key via AF_PACKET). If a socket is closed, all associated skbs will be cleaned

up.

This leads to a problem when a CAN driver calls can_put_echo_skb() on a

unshared SKB. If the socket is closed prior to the TX complete handler,

can_get_echo_skb() and the subsequent delivering of the echo SKB to all

registered callbacks, a SKB with a refcount of 0 is delivered.

To avoid the problem, in can_get_echo_skb() the original SKB is now always

cloned, regardless of shared SKB or not. If the process exists it can now

safely discard its SKBs, without disturbing the delivery of the echo SKB.

The problem shows up in the j1939 stack, when it clones the incoming skb, which

detects the already 0 refcount.

We can easily reproduce this with following example:

testj1939 -B -r can0: &

cansend can0 1823ff40#0123

Warning: CPU: 0 PID: 293 at lib/refcount.c:25 refcount_warn_saturate+0x108/0x174

Refcount_t: addition on 0; use-after-free.

Modules linked in: coda_vpu imx_vdoa videobuf2_vmalloc dw_hdmi_ahb_audio vcan

Cpu: 0 PID: 293 Comm: cansend Not tainted 5.5.0-rc6-00376-g9e20dcb7040d #1

Hardware name: Freescale i.MX6 Quad/DualLite (Device Tree)

Backtrace: 

[<c010f570>] (dump_backtrace) from [<c010f90c>] (show_stack+0x20/0x24)

[<c010f8ec>] (show_stack) from [<c0c3e1a4>] (dump_stack+0x8c/0xa0)

[<c0c3e118>] (dump_stack) from [<c0127fec>] (__warn+0xe0/0x108)

[<c0127f0c>] (__warn) from [<c01283c8>] (warn_slowpath_fmt+0xa8/0xcc)

[<c0128324>] (warn_slowpath_fmt) from [<c0539c0c>] (refcount_warn_saturate+0x108/0x174)

[<c0539b04>] (refcount_warn_saturate) from [<c0ad2cac>] (j1939_can_recv+0x20c/0x210)

[<c0ad2aa0>] (j1939_can_recv) from [<c0ac9dc8>] (can_rcv_filter+0xb4/0x268)

[<c0ac9d14>] (can_rcv_filter) from [<c0aca2cc>] (can_receive+0xb0/0xe4)

[<c0aca21c>] (can_receive) from [<c0aca348>] (can_rcv+0x48/0x98)

[<c0aca300>] (can_rcv) from [<c09b1fdc>] (__netif_receive_skb_one_core+0x64/0x88)

[<c09b1f78>] (__netif_receive_skb_one_core) from [<c09b2070>] (__netif_receive_skb+0x38/0x94)

[<c09b2038>] (__netif_receive_skb) from [<c09b2130>] (netif_receive_skb_internal+0x64/0xf8)

[<c09b20cc>] (netif_receive_skb_internal) from [<c09b21f8>] (netif_receive_skb+0x34/0x19c)

[<c09b21c4>] (netif_receive_skb) from [<c0791278>] (can_rx_offload_napi_poll+0x58/0xb4)

Fixes: 0ae89beb283a ("can: add destructor for self generated skbs")

Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>

Link: http://lore.kernel.org/r/20200124132656.22156-1-o.rempel@pengutronix.de

Acked-by: Oliver Hartkopp <socketcan@hartkopp.net>

Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

Acked-by: Takashi Iwai <tiwai@suse.de>

---

 include/linux/can/skb.h | 20 ++++++++------------

 1 file changed, 8 insertions(+), 12 deletions(-)

diff --git a/include/linux/can/skb.h b/include/linux/can/skb.h

index 900b9f4e0605..fc61cf4eff1c 100644

--- a/include/linux/can/skb.h

+++ b/include/linux/can/skb.h

@@ -61,21 +61,17 @@ static inline void can_skb_set_owner(struct sk_buff *skb, struct sock *sk)

  */

 static inline struct sk_buff *can_create_echo_skb(struct sk_buff *skb)

 {

-	if (skb_shared(skb)) {

-		struct sk_buff *nskb = skb_clone(skb, GFP_ATOMIC);

+	struct sk_buff *nskb;

-		if (likely(nskb)) {

-			can_skb_set_owner(nskb, skb->sk);

-			consume_skb(skb);

-			return nskb;

-		} else {

-			kfree_skb(skb);

-			return NULL;

-		}

+	nskb = skb_clone(skb, GFP_ATOMIC);

+	if (unlikely(!nskb)) {

+		kfree_skb(skb);

+		return NULL;

 	}

-	/* we can assume to have an unshared skb with proper owner */

-	return skb;

+	can_skb_set_owner(nskb, skb->sk);

+	consume_skb(skb);

+	return nskb;

 }

 #endif /* !_CAN_SKB_H */

-- 

2.16.4