Commit 25fe708b authored by Weiming Shi's avatar Weiming Shi Committed by Paolo Abeni
Browse files

net: team: fix NULL pointer dereference in team_xmit during mode change 



__team_change_mode() clears team->ops with memset() before restoring
safe dummy handlers via team_adjust_ops(). A concurrent team_xmit()
running under RCU on another CPU can read team->ops.transmit during
this window and call a NULL function pointer, crashing the kernel.

The race requires a mode change (CAP_NET_ADMIN) concurrent with
transmit on the team device.

 BUG: kernel NULL pointer dereference, address: 0000000000000000
 Oops: 0010 [#1] SMP KASAN NOPTI
 RIP: 0010:0x0
 Call Trace:
  team_xmit (drivers/net/team/team_core.c:1853)
  dev_hard_start_xmit (net/core/dev.c:3904)
  __dev_queue_xmit (net/core/dev.c:4871)
  packet_sendmsg (net/packet/af_packet.c:3109)
  __sys_sendto (net/socket.c:2265)

The original code assumed that no ports means no traffic, so mode
changes could freely memset()/memcpy() the ops.  AF_PACKET with
forced carrier breaks that assumption.

Prevent the race instead of making it safe: replace memset()/memcpy()
with per-field updates that never touch transmit or receive.  Those
two handlers are managed solely by team_adjust_ops(), which already
installs dummies when tx_en_port_count == 0 (always true during mode
change since no ports are present).  WRITE_ONCE/READ_ONCE prevent
store/load tearing on the handler pointers.

synchronize_net() before exit_op() drains in-flight readers that may
still reference old mode state from before port removal switched the
handlers to dummies.

Fixes: 3d249d4c ("net: introduce ethernet teaming device")
Reported-by: default avatarXiang Mei <xmei5@asu.edu>
Signed-off-by: default avatarWeiming Shi <bestswngs@gmail.com>
Reviewed-by: default avatarJiayuan Chen <jiayuan.chen@linux.dev>
Link: https://patch.msgid.link/20260521081159.1491563-3-bestswngs@gmail.com


Signed-off-by: default avatarPaolo Abeni <pabeni@redhat.com>
parent f2294260

drivers/net/team/team_core.c

+32 −13
Original line number Diff line number Diff line
@@ -534,21 +534,23 @@ static void team_adjust_ops(struct team *team) 


	if (!team->tx_en_port_count || !team_is_mode_set(team) ||

	    !team->mode->ops->transmit)

		team->ops.transmit = team_dummy_transmit;

		WRITE_ONCE(team->ops.transmit, team_dummy_transmit);

	else

		team->ops.transmit = team->mode->ops->transmit;

		WRITE_ONCE(team->ops.transmit, team->mode->ops->transmit);



	if (!team->rx_en_port_count || !team_is_mode_set(team) ||

	    !team->mode->ops->receive)

		team->ops.receive = team_dummy_receive;

		WRITE_ONCE(team->ops.receive, team_dummy_receive);

	else

		team->ops.receive = team->mode->ops->receive;

		WRITE_ONCE(team->ops.receive, team->mode->ops->receive);

}



/*

 * We can benefit from the fact that it's ensured no port is present

 * at the time of mode change. Therefore no packets are in fly so there's no

 * need to set mode operations in any special way.

 * team_change_mode() ensures no ports are present during mode change,

 * but lockless readers can still reach team_xmit().  Avoid touching

 * transmit/receive -- they are already set to dummies by

 * team_adjust_ops() since no ports are enabled.  synchronize_net()

 * drains in-flight readers before destroying old mode state.

 */

static int __team_change_mode(struct team *team,

			      const struct team_mode *new_mode)
@@ -557,9 +559,21 @@ static int __team_change_mode(struct team *team, 
	if (team_is_mode_set(team)) {

		void (*exit_op)(struct team *team) = team->ops.exit;



		/* Clear ops area so no callback is called any longer */

		memset(&team->ops, 0, sizeof(struct team_mode_ops));

		team_adjust_ops(team);

		/* Clear cold-path ops used only under RTNL.  transmit and

		 * receive are already dummies (no ports) so leave them

		 * alone -- overwriting them is the source of the race.

		 */

		team->ops.init = NULL;

		team->ops.exit = NULL;

		team->ops.port_enter = NULL;

		team->ops.port_leave = NULL;

		team->ops.port_change_dev_addr = NULL;

		team->ops.port_tx_disabled = NULL;



		/* Wait for in-flight readers before tearing down mode

		 * state they may reference.

		 */

		synchronize_net();



		if (exit_op)

			exit_op(team);
@@ -582,7 +596,12 @@ static int __team_change_mode(struct team *team, 
	}



	team->mode = new_mode;

	memcpy(&team->ops, new_mode->ops, sizeof(struct team_mode_ops));

	team->ops.init = new_mode->ops->init;

	team->ops.exit = new_mode->ops->exit;

	team->ops.port_enter = new_mode->ops->port_enter;

	team->ops.port_leave = new_mode->ops->port_leave;

	team->ops.port_change_dev_addr = new_mode->ops->port_change_dev_addr;

	team->ops.port_tx_disabled = new_mode->ops->port_tx_disabled;

	team_adjust_ops(team);



	return 0;
@@ -743,7 +762,7 @@ static rx_handler_result_t team_handle_frame(struct sk_buff **pskb) 
		/* allow exact match delivery for disabled ports */

		res = RX_HANDLER_EXACT;

	} else {

		res = team->ops.receive(team, port, skb);

		res = READ_ONCE(team->ops.receive)(team, port, skb);

	}

	if (res == RX_HANDLER_ANOTHER) {

		struct team_pcpu_stats *pcpu_stats;
@@ -1845,7 +1864,7 @@ static netdev_tx_t team_xmit(struct sk_buff *skb, struct net_device *dev) 


	tx_success = team_queue_override_transmit(team, skb);

	if (!tx_success)

		tx_success = team->ops.transmit(team, skb);

		tx_success = READ_ONCE(team->ops.transmit)(team, skb);

	if (tx_success) {

		struct team_pcpu_stats *pcpu_stats;