[PATCH net 2/3] can: fix unique skb identifier regression under RPS

[Marc Kleine-Budde <mkl@pengutronix.de>]

From: Oliver Hartkopp <socketcan@hartkopp.net>

Commit d4fb6514ff8e ("can: use skb hash instead of private variable in
headroom") moved the per-skb unique identifier used for raw_rcv()
duplicate detection into skb->hash.

With RPS enabled, get_rps_cpu() calls skb_get_hash() before the frame
reaches the CAN subsystem. Since CAN skbs have no L3/L4 headers, the
flow dissector assigns every CAN frame the same non-zero software
hash. can_set_skb_uid() only generated a new identifier when
skb->hash was 0, so it kept this constant hash. When the SLAB
allocator later reused the same skb address, raw_rcv() mistook the
next legitimate frame for a duplicate and dropped it.

Fix this by storing the CAN UID in the CAN skb extension
(struct can_skb_ext::can_skb_uid) instead of skb->hash, decoupling it
from any hash the network stack may compute. can_set_skb_uid() keeps
its "assign only if unset" behaviour, which preserves UIDs set before
transmission (e.g. by isotp to identify echo frames) across the local
loopback path.

Frames whose extension is shared with another clone (e.g. via tc mirred
or netem duplicate) are given a private extension copy before the UID
is assigned, so that independently received skb clones from real CAN
interfaces (can_skb_uid = 0) don't end up with the same UID.
The limitation that tc mirred/netem skb duplicates might be dropped in
raw_rcv for looped back isotp echo frame skbs is accepted. There is no
valid use-case for tc mirred or netem together with isotp which is not
capable to operate on different CAN interfaces simultaneously.
For routing and modifying CAN frames together with isotp use can-gw.

can-gw and vxcan additionally clear the UID of forwarded/duplicated
frames so each newly routed frame gets its own unique identifier.

Fixes: d4fb6514ff8e ("can: use skb hash instead of private variable in headroom")
Reported-by: Joerg Willmann <joe@clnt.de>
Closes: https://lore.kernel.org/linux-can/2859AD3D-C805-41A0-9036-C5E8EE152419@clnt.de/
Cc: stable@vger.kernel.org
Tested-by: Oliver Hartkopp <socketcan@hartkopp.net>
Tested-by: Joerg Willmann <joe@clnt.de>
Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>
Link: https://patch.msgid.link/20261001115724.27192-1-socketcan@hartkopp.net
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
---
 drivers/net/can/vxcan.c  |  3 +++
 include/linux/can/core.h |  3 ++-
 include/linux/can/skb.h  |  4 +++-
 include/net/can.h        |  2 ++
 net/can/af_can.c         | 47 ++++++++++++++++++++++++++++++----------
 net/can/gw.c             |  3 +++
 net/can/isotp.c          | 16 +++++++++-----
 net/can/raw.c            | 10 ++++++---
 8 files changed, 66 insertions(+), 22 deletions(-)

diff --git a/drivers/net/can/vxcan.c b/drivers/net/can/vxcan.c
index 9e2e25d02471..51148a81d1d9 100644
--- a/drivers/net/can/vxcan.c
+++ b/drivers/net/can/vxcan.c
@@ -79,6 +79,9 @@ static netdev_tx_t vxcan_xmit(struct sk_buff *oskb, struct net_device *dev)
 
 	/* reset CAN GW hop counter */
 	csx->can_gw_hops = 0;
+	/* start with new CAN skb UID in the other namespace */
+	csx->can_skb_uid = 0;
+
 	skb->pkt_type   = PACKET_BROADCAST;
 	skb->dev        = peer;
 	skb->ip_summed  = CHECKSUM_UNNECESSARY;
diff --git a/include/linux/can/core.h b/include/linux/can/core.h
index 3287232e3cad..2de74c2b78b6 100644
--- a/include/linux/can/core.h
+++ b/include/linux/can/core.h
@@ -17,6 +17,7 @@
 #include <linux/can.h>
 #include <linux/skbuff.h>
 #include <linux/netdevice.h>
+#include <net/can.h>
 
 #define DNAME(dev) ((dev) ? (dev)->name : "any")
 
@@ -58,7 +59,7 @@ extern void can_rx_unregister(struct net *net, struct net_device *dev,
 			      void *data);
 
 extern int can_send(struct sk_buff *skb, int loop);
-void can_set_skb_uid(struct sk_buff *skb);
+void can_set_skb_uid(struct can_skb_ext *csx);
 void can_sock_destruct(struct sock *sk);
 
 #endif /* !_CAN_CORE_H */
diff --git a/include/linux/can/skb.h b/include/linux/can/skb.h
index a70a02967071..5d27843862fc 100644
--- a/include/linux/can/skb.h
+++ b/include/linux/can/skb.h
@@ -43,8 +43,10 @@ static inline struct can_skb_ext *can_skb_ext_add(struct sk_buff *skb)
 	struct can_skb_ext *csx = skb_ext_add(skb, SKB_EXT_CAN);
 
 	/* skb_ext_add() returns uninitialized space */
-	if (csx)
+	if (csx) {
 		csx->can_gw_hops = 0;
+		csx->can_skb_uid = 0;
+	}
 
 	return csx;
 }
diff --git a/include/net/can.h b/include/net/can.h
index 6db9e826f0e0..2b8af2598732 100644
--- a/include/net/can.h
+++ b/include/net/can.h
@@ -17,12 +17,14 @@
  * @can_framelen: cached echo CAN frame length for bql
  * @can_gw_hops: can-gw CAN frame time-to-live counter
  * @can_ext_flags: CAN skb extensions flags
+ * @can_skb_uid: CAN skb UID for raw_rcv and isotp echo handling
  */
 struct can_skb_ext {
 	int	can_iif;
 	u16	can_framelen;
 	u8	can_gw_hops;
 	u8	can_ext_flags;
+	u32	can_skb_uid;
 };
 
 #endif /* _NET_CAN_H */
diff --git a/net/can/af_can.c b/net/can/af_can.c
index 7bc86b176b4d..34fe3b28d576 100644
--- a/net/can/af_can.c
+++ b/net/can/af_can.c
@@ -641,13 +641,10 @@ static int can_rcv_filter(struct can_dev_rcv_lists *dev_rcv_lists, struct sk_buf
 	return matches;
 }
 
-void can_set_skb_uid(struct sk_buff *skb)
+void can_set_skb_uid(struct can_skb_ext *csx)
 {
-	/* create non-zero unique skb identifier together with *skb */
-	while (!(skb->hash))
-		skb->hash = atomic_inc_return(&skbcounter);
-
-	skb->sw_hash = 1;
+	while (!(csx->can_skb_uid))
+		csx->can_skb_uid = atomic_inc_return(&skbcounter);
 }
 EXPORT_SYMBOL(can_set_skb_uid);
 
@@ -662,8 +659,6 @@ static void can_receive(struct sk_buff *skb, struct net_device *dev)
 	atomic_long_inc(&pkg_stats->rx_frames);
 	atomic_long_inc(&pkg_stats->rx_frames_delta);
 
-	can_set_skb_uid(skb);
-
 	rcu_read_lock();
 
 	/* deliver the packet to sockets listening on all devices */
@@ -687,8 +682,10 @@ static void can_receive(struct sk_buff *skb, struct net_device *dev)
 static int can_rcv(struct sk_buff *skb, struct net_device *dev,
 		   struct packet_type *pt, struct net_device *orig_dev)
 {
+	struct can_skb_ext *csx = can_skb_ext_find(skb);
+
 	if (unlikely(dev->type != ARPHRD_CAN || !can_get_ml_priv(dev) ||
-		     !can_skb_ext_find(skb) || !can_is_can_skb(skb))) {
+		     !csx || !can_is_can_skb(skb))) {
 		pr_warn_once("PF_CAN: dropped non conform CAN skbuff: dev type %d, len %d\n",
 			     dev->type, skb->len);
 
@@ -696,6 +693,14 @@ static int can_rcv(struct sk_buff *skb, struct net_device *dev,
 		return NET_RX_DROP;
 	}
 
+	/* create unshared CAN skb_extension for netem/mirred skb clones */
+	csx = skb_ext_add(skb, SKB_EXT_CAN);
+	if (unlikely(!csx)) {
+		kfree_skb_reason(skb, SKB_DROP_REASON_NOMEM);
+		return NET_RX_DROP;
+	}
+
+	can_set_skb_uid(csx);
 	can_receive(skb, dev);
 	return NET_RX_SUCCESS;
 }
@@ -703,8 +708,10 @@ static int can_rcv(struct sk_buff *skb, struct net_device *dev,
 static int canfd_rcv(struct sk_buff *skb, struct net_device *dev,
 		     struct packet_type *pt, struct net_device *orig_dev)
 {
+	struct can_skb_ext *csx = can_skb_ext_find(skb);
+
 	if (unlikely(dev->type != ARPHRD_CAN || !can_get_ml_priv(dev) ||
-		     !can_skb_ext_find(skb) || !can_is_canfd_skb(skb))) {
+		     !csx || !can_is_canfd_skb(skb))) {
 		pr_warn_once("PF_CAN: dropped non conform CAN FD skbuff: dev type %d, len %d\n",
 			     dev->type, skb->len);
 
@@ -712,6 +719,14 @@ static int canfd_rcv(struct sk_buff *skb, struct net_device *dev,
 		return NET_RX_DROP;
 	}
 
+	/* create unshared CAN skb_extension for netem/mirred skb clones */
+	csx = skb_ext_add(skb, SKB_EXT_CAN);
+	if (unlikely(!csx)) {
+		kfree_skb_reason(skb, SKB_DROP_REASON_NOMEM);
+		return NET_RX_DROP;
+	}
+
+	can_set_skb_uid(csx);
 	can_receive(skb, dev);
 	return NET_RX_SUCCESS;
 }
@@ -719,8 +734,10 @@ static int canfd_rcv(struct sk_buff *skb, struct net_device *dev,
 static int canxl_rcv(struct sk_buff *skb, struct net_device *dev,
 		     struct packet_type *pt, struct net_device *orig_dev)
 {
+	struct can_skb_ext *csx = can_skb_ext_find(skb);
+
 	if (unlikely(dev->type != ARPHRD_CAN || !can_get_ml_priv(dev) ||
-		     !can_skb_ext_find(skb) || !can_is_canxl_skb(skb))) {
+		     !csx || !can_is_canxl_skb(skb))) {
 		pr_warn_once("PF_CAN: dropped non conform CAN XL skbuff: dev type %d, len %d\n",
 			     dev->type, skb->len);
 
@@ -728,6 +745,14 @@ static int canxl_rcv(struct sk_buff *skb, struct net_device *dev,
 		return NET_RX_DROP;
 	}
 
+	/* create unshared CAN skb_extension for netem/mirred skb clones */
+	csx = skb_ext_add(skb, SKB_EXT_CAN);
+	if (unlikely(!csx)) {
+		kfree_skb_reason(skb, SKB_DROP_REASON_NOMEM);
+		return NET_RX_DROP;
+	}
+
+	can_set_skb_uid(csx);
 	can_receive(skb, dev);
 	return NET_RX_SUCCESS;
 }
diff --git a/net/can/gw.c b/net/can/gw.c
index 0ec99f68aa45..5793cb2420ed 100644
--- a/net/can/gw.c
+++ b/net/can/gw.c
@@ -527,6 +527,9 @@ static void can_can_gw_rcv(struct sk_buff *skb, void *data)
 	/* put the incremented hop counter in the cloned skb */
 	ncsx->can_gw_hops = csx->can_gw_hops + 1;
 
+	/* force a new CAN UID generation for the routed frame */
+	ncsx->can_skb_uid = 0;
+
 	/* first processing of this CAN frame -> adjust to private hop limit */
 	if (gwj->limit_hops && ncsx->can_gw_hops == 1)
 		ncsx->can_gw_hops = max_hops - gwj->limit_hops + 1;
diff --git a/net/can/isotp.c b/net/can/isotp.c
index 155530aedce2..f5dc9d04bd68 100644
--- a/net/can/isotp.c
+++ b/net/can/isotp.c
@@ -891,7 +891,7 @@ static void isotp_send_cframe(struct isotp_sock *so)
 	csx->can_iif = dev->ifindex;
 
 	/* set uid in tx skb to identify CF echo frames */
-	can_set_skb_uid(skb);
+	can_set_skb_uid(csx);
 
 	cf = (struct canfd_frame *)skb->data;
 	skb_put_zero(skb, so->ll.mtu);
@@ -917,7 +917,7 @@ static void isotp_send_cframe(struct isotp_sock *so)
 		pr_notice_once("can-isotp: cfecho is %08X != 0\n", old_cfecho);
 
 	/* set consecutive frame echo tag */
-	WRITE_ONCE(so->cfecho, skb->hash);
+	WRITE_ONCE(so->cfecho, csx->can_skb_uid);
 
 	/* send frame with local echo enabled */
 	can_send_ret = can_send(skb, 1);
@@ -969,18 +969,22 @@ static void isotp_rcv_echo(struct sk_buff *skb, void *data)
 {
 	struct sock *sk = (struct sock *)data;
 	struct isotp_sock *so = isotp_sk(sk);
+	struct can_skb_ext *csx = can_skb_ext_find(skb);
 
 	/* only handle my own local echo CF/SF skb's (no FF!) */
 	if (skb->sk != sk)
 		return;
 
+	if (WARN_ON_ONCE(!csx))
+		return;
+
 	/* unlike isotp_rcv_fc()/isotp_rcv_cf(), not already under so->rx_lock
 	 * (no isotp_rcv() caller here), so take it ourselves
 	 */
 	spin_lock(&so->rx_lock);
 
 	/* so->cfecho may since belong to a new transfer; recheck under lock */
-	if (READ_ONCE(so->cfecho) != skb->hash)
+	if (READ_ONCE(so->cfecho) != csx->can_skb_uid)
 		goto out_unlock;
 
 	/* cancel local echo timeout */
@@ -1222,7 +1226,7 @@ static int isotp_sendmsg(struct socket *sock, struct msghdr *msg, size_t size)
 	csx->can_iif = dev->ifindex;
 
 	/* set uid in tx skb to identify CF echo frames */
-	can_set_skb_uid(skb);
+	can_set_skb_uid(csx);
 
 	so->tx.len = size;
 	so->tx.idx = 0;
@@ -1261,7 +1265,7 @@ static int isotp_sendmsg(struct socket *sock, struct msghdr *msg, size_t size)
 			cf->data[ae] |= size;
 
 		/* set CF echo tag for isotp_rcv_echo() (SF-mode) */
-		WRITE_ONCE(so->cfecho, skb->hash);
+		WRITE_ONCE(so->cfecho, csx->can_skb_uid);
 	} else {
 		/* send first frame */
 
@@ -1278,7 +1282,7 @@ static int isotp_sendmsg(struct socket *sock, struct msghdr *msg, size_t size)
 			so->txfc.bs = 0;
 
 			/* set CF echo tag for isotp_rcv_echo() (CF-mode) */
-			WRITE_ONCE(so->cfecho, skb->hash);
+			WRITE_ONCE(so->cfecho, csx->can_skb_uid);
 		} else {
 			/* standard flow control check */
 			new_state = ISOTP_WAIT_FIRST_FC;
diff --git a/net/can/raw.c b/net/can/raw.c
index 82d9c0499c95..0acd4f6c6dd6 100644
--- a/net/can/raw.c
+++ b/net/can/raw.c
@@ -77,7 +77,7 @@ MODULE_ALIAS("can-proto-1");
 
 struct uniqframe {
 	const struct sk_buff *skb;
-	u32 hash;
+	u32 can_skb_uid;
 	unsigned int join_rx_count;
 };
 
@@ -133,12 +133,16 @@ static void raw_rcv(struct sk_buff *oskb, void *data)
 	enum skb_drop_reason reason;
 	struct sockaddr_can *addr;
 	struct sk_buff *skb;
+	struct can_skb_ext *csx = can_skb_ext_find(oskb);
 	unsigned int *pflags;
 
 	/* check the received tx sock reference */
 	if (!ro->recv_own_msgs && oskb->sk == sk)
 		return;
 
+	if (WARN_ON_ONCE(!csx))
+		return;
+
 	/* make sure to not pass oversized frames to the socket */
 	if (!ro->fd_frames && can_is_canfd_skb(oskb))
 		return;
@@ -165,7 +169,7 @@ static void raw_rcv(struct sk_buff *oskb, void *data)
 
 	/* eliminate multiple filter matches for the same skb */
 	if (this_cpu_ptr(ro->uniq)->skb == oskb &&
-	    this_cpu_ptr(ro->uniq)->hash == oskb->hash) {
+	    this_cpu_ptr(ro->uniq)->can_skb_uid == csx->can_skb_uid) {
 		if (!ro->join_filters)
 			return;
 
@@ -175,7 +179,7 @@ static void raw_rcv(struct sk_buff *oskb, void *data)
 			return;
 	} else {
 		this_cpu_ptr(ro->uniq)->skb = oskb;
-		this_cpu_ptr(ro->uniq)->hash = oskb->hash;
+		this_cpu_ptr(ro->uniq)->can_skb_uid = csx->can_skb_uid;
 		this_cpu_ptr(ro->uniq)->join_rx_count = 1;
 		/* drop first frame to check all enabled filters? */
 		if (ro->join_filters && ro->count > 1)
-- 
2.53.0