[PATCH 5.14 316/849] net: annotate data-race in neigh_output()

Greg Kroah-Hartman
2021-11-15T22:53:52Z

From: Eric Dumazet <edumazet@google.com>

[ Upstream commit d18785e213866935b4c3dc0c33c3e18801ce0ce8 ]

neigh_output() reads n->nud_state and hh->hh_len locklessly.

This is fine, but we need to add annotations and document this.

We evaluate skip_cache first to avoid reading these fields
if the cache has to by bypassed.

syzbot report:

BUG: KCSAN: data-race in __neigh_event_send / ip_finish_output2

write to 0xffff88810798a885 of 1 bytes by interrupt on cpu 1:
__neigh_event_send+0x40d/0xac0 net/core/neighbour.c:1128
neigh_event_send include/net/neighbour.h:444 [inline]
neigh_resolve_output+0x104/0x410 net/core/neighbour.c:1476
neigh_output include/net/neighbour.h:510 [inline]
ip_finish_output2+0x80a/0xaa0 net/ipv4/ip_output.c:221
ip_finish_output+0x3b5/0x510 net/ipv4/ip_output.c:309
NF_HOOK_COND include/linux/netfilter.h:296 [inline]
ip_output+0xf3/0x1a0 net/ipv4/ip_output.c:423
dst_output include/net/dst.h:450 [inline]
ip_local_out+0x164/0x220 net/ipv4/ip_output.c:126
__ip_queue_xmit+0x9d3/0xa20 net/ipv4/ip_output.c:525
ip_queue_xmit+0x34/0x40 net/ipv4/ip_output.c:539
__tcp_transmit_skb+0x142a/0x1a00 net/ipv4/tcp_output.c:1405
tcp_transmit_skb net/ipv4/tcp_output.c:1423 [inline]
tcp_xmit_probe_skb net/ipv4/tcp_output.c:4011 [inline]
tcp_write_wakeup+0x4a9/0x810 net/ipv4/tcp_output.c:4064
tcp_send_probe0+0x2c/0x2b0 net/ipv4/tcp_output.c:4079
tcp_probe_timer net/ipv4/tcp_timer.c:398 [inline]
tcp_write_timer_handler+0x394/0x520 net/ipv4/tcp_timer.c:626
tcp_write_timer+0xb9/0x180 net/ipv4/tcp_timer.c:642
call_timer_fn+0x2e/0x1d0 kernel/time/timer.c:1421
expire_timers+0x135/0x240 kernel/time/timer.c:1466
__run_timers+0x368/0x430 kernel/time/timer.c:1734
run_timer_softirq+0x19/0x30 kernel/time/timer.c:1747
__do_softirq+0x12c/0x26e kernel/softirq.c:558
invoke_softirq kernel/softirq.c:432 [inline]
__irq_exit_rcu kernel/softirq.c:636 [inline]
irq_exit_rcu+0x4e/0xa0 kernel/softirq.c:648
sysvec_apic_timer_interrupt+0x69/0x80 arch/x86/kernel/apic/apic.c:1097
asm_sysvec_apic_timer_interrupt+0x12/0x20
native_safe_halt arch/x86/include/asm/irqflags.h:51 [inline]
arch_safe_halt arch/x86/include/asm/irqflags.h:89 [inline]
acpi_safe_halt drivers/acpi/processor_idle.c:109 [inline]
acpi_idle_do_entry drivers/acpi/processor_idle.c:553 [inline]
acpi_idle_enter+0x258/0x2e0 drivers/acpi/processor_idle.c:688
cpuidle_enter_state+0x2b4/0x760 drivers/cpuidle/cpuidle.c:237
cpuidle_enter+0x3c/0x60 drivers/cpuidle/cpuidle.c:351
call_cpuidle kernel/sched/idle.c:158 [inline]
cpuidle_idle_call kernel/sched/idle.c:239 [inline]
do_idle+0x1a3/0x250 kernel/sched/idle.c:306
cpu_startup_entry+0x15/0x20 kernel/sched/idle.c:403
secondary_startup_64_no_verify+0xb1/0xbb

read to 0xffff88810798a885 of 1 bytes by interrupt on cpu 0:
neigh_output include/net/neighbour.h:507 [inline]
ip_finish_output2+0x79a/0xaa0 net/ipv4/ip_output.c:221
ip_finish_output+0x3b5/0x510 net/ipv4/ip_output.c:309
NF_HOOK_COND include/linux/netfilter.h:296 [inline]
ip_output+0xf3/0x1a0 net/ipv4/ip_output.c:423
dst_output include/net/dst.h:450 [inline]
ip_local_out+0x164/0x220 net/ipv4/ip_output.c:126
__ip_queue_xmit+0x9d3/0xa20 net/ipv4/ip_output.c:525
ip_queue_xmit+0x34/0x40 net/ipv4/ip_output.c:539
__tcp_transmit_skb+0x142a/0x1a00 net/ipv4/tcp_output.c:1405
tcp_transmit_skb net/ipv4/tcp_output.c:1423 [inline]
tcp_xmit_probe_skb net/ipv4/tcp_output.c:4011 [inline]
tcp_write_wakeup+0x4a9/0x810 net/ipv4/tcp_output.c:4064
tcp_send_probe0+0x2c/0x2b0 net/ipv4/tcp_output.c:4079
tcp_probe_timer net/ipv4/tcp_timer.c:398 [inline]
tcp_write_timer_handler+0x394/0x520 net/ipv4/tcp_timer.c:626
tcp_write_timer+0xb9/0x180 net/ipv4/tcp_timer.c:642
call_timer_fn+0x2e/0x1d0 kernel/time/timer.c:1421
expire_timers+0x135/0x240 kernel/time/timer.c:1466
__run_timers+0x368/0x430 kernel/time/timer.c:1734
run_timer_softirq+0x19/0x30 kernel/time/timer.c:1747
__do_softirq+0x12c/0x26e kernel/softirq.c:558
invoke_softirq kernel/softirq.c:432 [inline]
__irq_exit_rcu kernel/softirq.c:636 [inline]
irq_exit_rcu+0x4e/0xa0 kernel/softirq.c:648
sysvec_apic_timer_interrupt+0x69/0x80 arch/x86/kernel/apic/apic.c:1097
asm_sysvec_apic_timer_interrupt+0x12/0x20
native_safe_halt arch/x86/include/asm/irqflags.h:51 [inline]
arch_safe_halt arch/x86/include/asm/irqflags.h:89 [inline]
acpi_safe_halt drivers/acpi/processor_idle.c:109 [inline]
acpi_idle_do_entry drivers/acpi/processor_idle.c:553 [inline]
acpi_idle_enter+0x258/0x2e0 drivers/acpi/processor_idle.c:688
cpuidle_enter_state+0x2b4/0x760 drivers/cpuidle/cpuidle.c:237
cpuidle_enter+0x3c/0x60 drivers/cpuidle/cpuidle.c:351
call_cpuidle kernel/sched/idle.c:158 [inline]
cpuidle_idle_call kernel/sched/idle.c:239 [inline]
do_idle+0x1a3/0x250 kernel/sched/idle.c:306
cpu_startup_entry+0x15/0x20 kernel/sched/idle.c:403
rest_init+0xee/0x100 init/main.c:734
arch_call_rest_init+0xa/0xb
start_kernel+0x5e4/0x669 init/main.c:1142
secondary_startup_64_no_verify+0xb1/0xbb

value changed: 0x20 -> 0x01

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 0 Comm: swapper/0 Not tainted 5.15.0-rc6-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: syzbot <syzkaller@googlegroups.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
include/net/neighbour.h | 11 ++++++++---
1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/include/net/neighbour.h b/include/net/neighbour.h
index 22ced1381ede5..990f9b1d17092 100644
--- a/include/net/neighbour.h
+++ b/include/net/neighbour.h
@@ -504,10 +504,15 @@ static inline int neigh_output(struct neighbour *n, struct sk_buff *skb,
{
const struct hh_cache *hh = &n->hh;

- if ((n->nud_state & NUD_CONNECTED) && hh->hh_len && !skip_cache)
+ /* n->nud_state and hh->hh_len could be changed under us.
+ * neigh_hh_output() is taking care of the race later.
+ */
+ if (!skip_cache &&
+ (READ_ONCE(n->nud_state) & NUD_CONNECTED) &&
+ READ_ONCE(hh->hh_len))
return neigh_hh_output(hh, skb);
- else
- return n->output(n, skb);
+
+ return n->output(n, skb);
}

static inline struct neighbour *
--
2.33.0