net: annotate data-races on txq->xmit_lock_owner

edumazet · kuba-moo · commit 7a10d8c810cf · 2021-12-01T19:14:26.000-08:00
syzbot found that __dev_queue_xmit() is reading txq->xmit_lock_owner without annotations. No serious issue there, let's document what is happening there. BUG: KCSAN: data-race in __dev_queue_xmit / __dev_queue_xmit write to 0xffff888139d09484 of 4 bytes by interrupt on cpu 0: __netif_tx_unlock include/linux/netdevice.h:4437 [inline] __dev_queue_xmit+0x948/0xf70 net/core/dev.c:4229 dev_queue_xmit_accel+0x19/0x20 net/core/dev.c:4265 macvlan_queue_xmit drivers/net/macvlan.c:543 [inline] macvlan_start_xmit+0x2b3/0x3d0 drivers/net/macvlan.c:567 __netdev_start_xmit include/linux/netdevice.h:4987 [inline] netdev_start_xmit include/linux/netdevice.h:5001 [inline] xmit_one+0x105/0x2f0 net/core/dev.c:3590 dev_hard_start_xmit+0x72/0x120 net/core/dev.c:3606 sch_direct_xmit+0x1b2/0x7c0 net/sched/sch_generic.c:342 __dev_xmit_skb+0x83d/0x1370 net/core/dev.c:3817 __dev_queue_xmit+0x590/0xf70 net/core/dev.c:4194 dev_queue_xmit+0x13/0x20 net/core/dev.c:4259 neigh_hh_output include/net/neighbour.h:511 [inline] neigh_output include/net/neighbour.h:525 [inline] ip6_finish_output2+0x995/0xbb0 net/ipv6/ip6_output.c:126 __ip6_finish_output net/ipv6/ip6_output.c:191 [inline] ip6_finish_output+0x444/0x4c0 net/ipv6/ip6_output.c:201 NF_HOOK_COND include/linux/netfilter.h:296 [inline] ip6_output+0x10e/0x210 net/ipv6/ip6_output.c:224 dst_output include/net/dst.h:450 [inline] NF_HOOK include/linux/netfilter.h:307 [inline] ndisc_send_skb+0x486/0x610 net/ipv6/ndisc.c:508 ndisc_send_rs+0x3b0/0x3e0 net/ipv6/ndisc.c:702 addrconf_rs_timer+0x370/0x540 net/ipv6/addrconf.c:3898 call_timer_fn+0x2e/0x240 kernel/time/timer.c:1421 expire_timers+0x116/0x240 kernel/time/timer.c:1466 __run_timers+0x368/0x410 kernel/time/timer.c:1734 run_timer_softirq+0x2e/0x60 kernel/time/timer.c:1747 __do_softirq+0x158/0x2de kernel/softirq.c:558 __irq_exit_rcu kernel/softirq.c:636 [inline] irq_exit_rcu+0x37/0x70 kernel/softirq.c:648 sysvec_apic_timer_interrupt+0x3e/0xb0 arch/x86/kernel/apic/apic.c:1097 asm_sysvec_apic_timer_interrupt+0x12/0x20 read to 0xffff888139d09484 of 4 bytes by interrupt on cpu 1: __dev_queue_xmit+0x5e3/0xf70 net/core/dev.c:4213 dev_queue_xmit_accel+0x19/0x20 net/core/dev.c:4265 macvlan_queue_xmit drivers/net/macvlan.c:543 [inline] macvlan_start_xmit+0x2b3/0x3d0 drivers/net/macvlan.c:567 __netdev_start_xmit include/linux/netdevice.h:4987 [inline] netdev_start_xmit include/linux/netdevice.h:5001 [inline] xmit_one+0x105/0x2f0 net/core/dev.c:3590 dev_hard_start_xmit+0x72/0x120 net/core/dev.c:3606 sch_direct_xmit+0x1b2/0x7c0 net/sched/sch_generic.c:342 __dev_xmit_skb+0x83d/0x1370 net/core/dev.c:3817 __dev_queue_xmit+0x590/0xf70 net/core/dev.c:4194 dev_queue_xmit+0x13/0x20 net/core/dev.c:4259 neigh_resolve_output+0x3db/0x410 net/core/neighbour.c:1523 neigh_output include/net/neighbour.h:527 [inline] ip6_finish_output2+0x9be/0xbb0 net/ipv6/ip6_output.c:126 __ip6_finish_output net/ipv6/ip6_output.c:191 [inline] ip6_finish_output+0x444/0x4c0 net/ipv6/ip6_output.c:201 NF_HOOK_COND include/linux/netfilter.h:296 [inline] ip6_output+0x10e/0x210 net/ipv6/ip6_output.c:224 dst_output include/net/dst.h:450 [inline] NF_HOOK include/linux/netfilter.h:307 [inline] ndisc_send_skb+0x486/0x610 net/ipv6/ndisc.c:508 ndisc_send_rs+0x3b0/0x3e0 net/ipv6/ndisc.c:702 addrconf_rs_timer+0x370/0x540 net/ipv6/addrconf.c:3898 call_timer_fn+0x2e/0x240 kernel/time/timer.c:1421 expire_timers+0x116/0x240 kernel/time/timer.c:1466 __run_timers+0x368/0x410 kernel/time/timer.c:1734 run_timer_softirq+0x2e/0x60 kernel/time/timer.c:1747 __do_softirq+0x158/0x2de kernel/softirq.c:558 __irq_exit_rcu kernel/softirq.c:636 [inline] irq_exit_rcu+0x37/0x70 kernel/softirq.c:648 sysvec_apic_timer_interrupt+0x8d/0xb0 arch/x86/kernel/apic/apic.c:1097 asm_sysvec_apic_timer_interrupt+0x12/0x20 kcsan_setup_watchpoint+0x94/0x420 kernel/kcsan/core.c:443 folio_test_anon include/linux/page-flags.h:581 [inline] PageAnon include/linux/page-flags.h:586 [inline] zap_pte_range+0x5ac/0x10e0 mm/memory.c:1347 zap_pmd_range mm/memory.c:1467 [inline] zap_pud_range mm/memory.c:1496 [inline] zap_p4d_range mm/memory.c:1517 [inline] unmap_page_range+0x2dc/0x3d0 mm/memory.c:1538 unmap_single_vma+0x157/0x210 mm/memory.c:1583 unmap_vmas+0xd0/0x180 mm/memory.c:1615 exit_mmap+0x23d/0x470 mm/mmap.c:3170 __mmput+0x27/0x1b0 kernel/fork.c:1113 mmput+0x3d/0x50 kernel/fork.c:1134 exit_mm+0xdb/0x170 kernel/exit.c:507 do_exit+0x608/0x17a0 kernel/exit.c:819 do_group_exit+0xce/0x180 kernel/exit.c:929 get_signal+0xfc3/0x1550 kernel/signal.c:2852 arch_do_signal_or_restart+0x8c/0x2e0 arch/x86/kernel/signal.c:868 handle_signal_work kernel/entry/common.c:148 [inline] exit_to_user_mode_loop kernel/entry/common.c:172 [inline] exit_to_user_mode_prepare+0x113/0x190 kernel/entry/common.c:207 __syscall_exit_to_user_mode_work kernel/entry/common.c:289 [inline] syscall_exit_to_user_mode+0x20/0x40 kernel/entry/common.c:300 do_syscall_64+0x50/0xd0 arch/x86/entry/common.c:86 entry_SYSCALL_64_after_hwframe+0x44/0xae value changed: 0x00000000 -> 0xffffffff Reported by Kernel Concurrency Sanitizer on: CPU: 1 PID: 28712 Comm: syz-executor.0 Tainted: G W 5.16.0-rc1-syzkaller #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 Fixes: 1da177e ("Linux-2.6.12-rc2") Signed-off-by: Eric Dumazet <edumazet@google.com> Reported-by: syzbot <syzkaller@googlegroups.com> Link: https://lore.kernel.org/r/20211130170155.2331929-1-eric.dumazet@gmail.com Signed-off-by: Jakub Kicinski <kuba@kernel.org>
diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
@@ -4404,7 +4404,8 @@ static inline u32 netif_msg_init(int debug_value, int default_msg_enable_bits)
 static inline void __netif_tx_lock(struct netdev_queue *txq, int cpu)
 {
 	spin_lock(&txq->_xmit_lock);
-	txq->xmit_lock_owner = cpu;
+	/* Pairs with READ_ONCE() in __dev_queue_xmit() */
+	WRITE_ONCE(txq->xmit_lock_owner, cpu);
 }
 
 static inline bool __netif_tx_acquire(struct netdev_queue *txq)
@@ -4421,26 +4422,32 @@ static inline void __netif_tx_release(struct netdev_queue *txq)
 static inline void __netif_tx_lock_bh(struct netdev_queue *txq)
 {
 	spin_lock_bh(&txq->_xmit_lock);
-	txq->xmit_lock_owner = smp_processor_id();
+	/* Pairs with READ_ONCE() in __dev_queue_xmit() */
+	WRITE_ONCE(txq->xmit_lock_owner, smp_processor_id());
 }
 
 static inline bool __netif_tx_trylock(struct netdev_queue *txq)
 {
 	bool ok = spin_trylock(&txq->_xmit_lock);
-	if (likely(ok))
-		txq->xmit_lock_owner = smp_processor_id();
+
+	if (likely(ok)) {
+		/* Pairs with READ_ONCE() in __dev_queue_xmit() */
+		WRITE_ONCE(txq->xmit_lock_owner, smp_processor_id());
+	}
 	return ok;
 }
 
 static inline void __netif_tx_unlock(struct netdev_queue *txq)
 {
-	txq->xmit_lock_owner = -1;
+	/* Pairs with READ_ONCE() in __dev_queue_xmit() */
+	WRITE_ONCE(txq->xmit_lock_owner, -1);
 	spin_unlock(&txq->_xmit_lock);
 }
 
 static inline void __netif_tx_unlock_bh(struct netdev_queue *txq)
 {
-	txq->xmit_lock_owner = -1;
+	/* Pairs with READ_ONCE() in __dev_queue_xmit() */
+	WRITE_ONCE(txq->xmit_lock_owner, -1);
 	spin_unlock_bh(&txq->_xmit_lock);
 }
 
diff --git a/net/core/dev.c b/net/core/dev.c
@@ -4210,7 +4210,10 @@ static int __dev_queue_xmit(struct sk_buff *skb, struct net_device *sb_dev)
 	if (dev->flags & IFF_UP) {
 		int cpu = smp_processor_id(); /* ok because BHs are off */
 
-		if (txq->xmit_lock_owner != cpu) {
+		/* Other cpus might concurrently change txq->xmit_lock_owner
+		 * to -1 or to their cpu id, but not to our id.
+		 */
+		if (READ_ONCE(txq->xmit_lock_owner) != cpu) {
 			if (dev_xmit_recursion())
 				goto recursion_alert;
 

Original file line number	Diff line number	Diff line change
`@@ -4404,7 +4404,8 @@ static inline u32 netif_msg_init(int debug_value, int default_msg_enable_bits)`
`4404`	`4404`	`static inline void __netif_tx_lock(struct netdev_queue *txq, int cpu)`
`4405`	`4405`	`{`
`4406`	`4406`	`spin_lock(&txq->_xmit_lock);`
`4407`		`- txq->xmit_lock_owner = cpu;`
	`4407`	`+ /* Pairs with READ_ONCE() in __dev_queue_xmit() */`
	`4408`	`+ WRITE_ONCE(txq->xmit_lock_owner, cpu);`
`4408`	`4409`	`}`
`4409`	`4410`
`4410`	`4411`	`static inline bool __netif_tx_acquire(struct netdev_queue *txq)`
`@@ -4421,26 +4422,32 @@ static inline void __netif_tx_release(struct netdev_queue *txq)`
`4421`	`4422`	`static inline void __netif_tx_lock_bh(struct netdev_queue *txq)`
`4422`	`4423`	`{`
`4423`	`4424`	`spin_lock_bh(&txq->_xmit_lock);`
`4424`		`- txq->xmit_lock_owner = smp_processor_id();`
	`4425`	`+ /* Pairs with READ_ONCE() in __dev_queue_xmit() */`
	`4426`	`+ WRITE_ONCE(txq->xmit_lock_owner, smp_processor_id());`
`4425`	`4427`	`}`
`4426`	`4428`
`4427`	`4429`	`static inline bool __netif_tx_trylock(struct netdev_queue *txq)`
`4428`	`4430`	`{`
`4429`	`4431`	`bool ok = spin_trylock(&txq->_xmit_lock);`
`4430`		`- if (likely(ok))`
`4431`		`- txq->xmit_lock_owner = smp_processor_id();`
	`4432`	`+`
	`4433`	`+ if (likely(ok)) {`
	`4434`	`+ /* Pairs with READ_ONCE() in __dev_queue_xmit() */`
	`4435`	`+ WRITE_ONCE(txq->xmit_lock_owner, smp_processor_id());`
	`4436`	`+ }`
`4432`	`4437`	`return ok;`
`4433`	`4438`	`}`
`4434`	`4439`
`4435`	`4440`	`static inline void __netif_tx_unlock(struct netdev_queue *txq)`
`4436`	`4441`	`{`
`4437`		`- txq->xmit_lock_owner = -1;`
	`4442`	`+ /* Pairs with READ_ONCE() in __dev_queue_xmit() */`
	`4443`	`+ WRITE_ONCE(txq->xmit_lock_owner, -1);`
`4438`	`4444`	`spin_unlock(&txq->_xmit_lock);`
`4439`	`4445`	`}`
`4440`	`4446`
`4441`	`4447`	`static inline void __netif_tx_unlock_bh(struct netdev_queue *txq)`
`4442`	`4448`	`{`
`4443`		`- txq->xmit_lock_owner = -1;`
	`4449`	`+ /* Pairs with READ_ONCE() in __dev_queue_xmit() */`
	`4450`	`+ WRITE_ONCE(txq->xmit_lock_owner, -1);`
`4444`	`4451`	`spin_unlock_bh(&txq->_xmit_lock);`
`4445`	`4452`	`}`
`4446`	`4453`