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Subject[PATCH 5.4 141/191] net: icmp: fix data-race in cmp_global_allow()
Date
From: Eric Dumazet <edumazet@google.com>

commit bbab7ef235031f6733b5429ae7877bfa22339712 upstream.

This code reads two global variables without protection
of a lock. We need READ_ONCE()/WRITE_ONCE() pairs to
avoid load/store-tearing and better document the intent.

KCSAN reported :
BUG: KCSAN: data-race in icmp_global_allow / icmp_global_allow

read to 0xffffffff861a8014 of 4 bytes by task 11201 on cpu 0:
icmp_global_allow+0x36/0x1b0 net/ipv4/icmp.c:254
icmpv6_global_allow net/ipv6/icmp.c:184 [inline]
icmpv6_global_allow net/ipv6/icmp.c:179 [inline]
icmp6_send+0x493/0x1140 net/ipv6/icmp.c:514
icmpv6_send+0x71/0xb0 net/ipv6/ip6_icmp.c:43
ip6_link_failure+0x43/0x180 net/ipv6/route.c:2640
dst_link_failure include/net/dst.h:419 [inline]
vti_xmit net/ipv4/ip_vti.c:243 [inline]
vti_tunnel_xmit+0x27f/0xa50 net/ipv4/ip_vti.c:279
__netdev_start_xmit include/linux/netdevice.h:4420 [inline]
netdev_start_xmit include/linux/netdevice.h:4434 [inline]
xmit_one net/core/dev.c:3280 [inline]
dev_hard_start_xmit+0xef/0x430 net/core/dev.c:3296
__dev_queue_xmit+0x14c9/0x1b60 net/core/dev.c:3873
dev_queue_xmit+0x21/0x30 net/core/dev.c:3906
neigh_direct_output+0x1f/0x30 net/core/neighbour.c:1530
neigh_output include/net/neighbour.h:511 [inline]
ip6_finish_output2+0x7a6/0xec0 net/ipv6/ip6_output.c:116
__ip6_finish_output net/ipv6/ip6_output.c:142 [inline]
__ip6_finish_output+0x2d7/0x330 net/ipv6/ip6_output.c:127
ip6_finish_output+0x41/0x160 net/ipv6/ip6_output.c:152
NF_HOOK_COND include/linux/netfilter.h:294 [inline]
ip6_output+0xf2/0x280 net/ipv6/ip6_output.c:175
dst_output include/net/dst.h:436 [inline]
ip6_local_out+0x74/0x90 net/ipv6/output_core.c:179

write to 0xffffffff861a8014 of 4 bytes by task 11183 on cpu 1:
icmp_global_allow+0x174/0x1b0 net/ipv4/icmp.c:272
icmpv6_global_allow net/ipv6/icmp.c:184 [inline]
icmpv6_global_allow net/ipv6/icmp.c:179 [inline]
icmp6_send+0x493/0x1140 net/ipv6/icmp.c:514
icmpv6_send+0x71/0xb0 net/ipv6/ip6_icmp.c:43
ip6_link_failure+0x43/0x180 net/ipv6/route.c:2640
dst_link_failure include/net/dst.h:419 [inline]
vti_xmit net/ipv4/ip_vti.c:243 [inline]
vti_tunnel_xmit+0x27f/0xa50 net/ipv4/ip_vti.c:279
__netdev_start_xmit include/linux/netdevice.h:4420 [inline]
netdev_start_xmit include/linux/netdevice.h:4434 [inline]
xmit_one net/core/dev.c:3280 [inline]
dev_hard_start_xmit+0xef/0x430 net/core/dev.c:3296
__dev_queue_xmit+0x14c9/0x1b60 net/core/dev.c:3873
dev_queue_xmit+0x21/0x30 net/core/dev.c:3906
neigh_direct_output+0x1f/0x30 net/core/neighbour.c:1530
neigh_output include/net/neighbour.h:511 [inline]
ip6_finish_output2+0x7a6/0xec0 net/ipv6/ip6_output.c:116
__ip6_finish_output net/ipv6/ip6_output.c:142 [inline]
__ip6_finish_output+0x2d7/0x330 net/ipv6/ip6_output.c:127
ip6_finish_output+0x41/0x160 net/ipv6/ip6_output.c:152
NF_HOOK_COND include/linux/netfilter.h:294 [inline]
ip6_output+0xf2/0x280 net/ipv6/ip6_output.c:175

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 11183 Comm: syz-executor.2 Not tainted 5.4.0-rc3+ #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011

Fixes: 4cdf507d5452 ("icmp: add a global rate limitation")
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: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
net/ipv4/icmp.c | 11 ++++++-----
1 file changed, 6 insertions(+), 5 deletions(-)

--- a/net/ipv4/icmp.c
+++ b/net/ipv4/icmp.c
@@ -249,10 +249,11 @@ bool icmp_global_allow(void)
bool rc = false;

/* Check if token bucket is empty and cannot be refilled
- * without taking the spinlock.
+ * without taking the spinlock. The READ_ONCE() are paired
+ * with the following WRITE_ONCE() in this same function.
*/
- if (!icmp_global.credit) {
- delta = min_t(u32, now - icmp_global.stamp, HZ);
+ if (!READ_ONCE(icmp_global.credit)) {
+ delta = min_t(u32, now - READ_ONCE(icmp_global.stamp), HZ);
if (delta < HZ / 50)
return false;
}
@@ -262,14 +263,14 @@ bool icmp_global_allow(void)
if (delta >= HZ / 50) {
incr = sysctl_icmp_msgs_per_sec * delta / HZ ;
if (incr)
- icmp_global.stamp = now;
+ WRITE_ONCE(icmp_global.stamp, now);
}
credit = min_t(u32, icmp_global.credit + incr, sysctl_icmp_msgs_burst);
if (credit) {
credit--;
rc = true;
}
- icmp_global.credit = credit;
+ WRITE_ONCE(icmp_global.credit, credit);
spin_unlock(&icmp_global.lock);
return rc;
}

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