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Subject[PATCH 4.14 71/74] net: add annotations on hh->hh_len lockless accesses
Date
From: Eric Dumazet <edumazet@google.com>

[ Upstream commit c305c6ae79e2ce20c22660ceda94f0d86d639a82 ]

KCSAN reported a data-race [1]

While we can use READ_ONCE() on the read sides,
we need to make sure hh->hh_len is written last.

[1]

BUG: KCSAN: data-race in eth_header_cache / neigh_resolve_output

write to 0xffff8880b9dedcb8 of 4 bytes by task 29760 on cpu 0:
eth_header_cache+0xa9/0xd0 net/ethernet/eth.c:247
neigh_hh_init net/core/neighbour.c:1463 [inline]
neigh_resolve_output net/core/neighbour.c:1480 [inline]
neigh_resolve_output+0x415/0x470 net/core/neighbour.c:1470
neigh_output include/net/neighbour.h:511 [inline]
ip6_finish_output2+0x7a2/0xec0 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]
NF_HOOK include/linux/netfilter.h:305 [inline]
ndisc_send_skb+0x459/0x5f0 net/ipv6/ndisc.c:505
ndisc_send_ns+0x207/0x430 net/ipv6/ndisc.c:647
rt6_probe_deferred+0x98/0xf0 net/ipv6/route.c:615
process_one_work+0x3d4/0x890 kernel/workqueue.c:2269
worker_thread+0xa0/0x800 kernel/workqueue.c:2415
kthread+0x1d4/0x200 drivers/block/aoe/aoecmd.c:1253
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:352

read to 0xffff8880b9dedcb8 of 4 bytes by task 29572 on cpu 1:
neigh_resolve_output net/core/neighbour.c:1479 [inline]
neigh_resolve_output+0x113/0x470 net/core/neighbour.c:1470
neigh_output include/net/neighbour.h:511 [inline]
ip6_finish_output2+0x7a2/0xec0 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]
NF_HOOK include/linux/netfilter.h:305 [inline]
ndisc_send_skb+0x459/0x5f0 net/ipv6/ndisc.c:505
ndisc_send_ns+0x207/0x430 net/ipv6/ndisc.c:647
rt6_probe_deferred+0x98/0xf0 net/ipv6/route.c:615
process_one_work+0x3d4/0x890 kernel/workqueue.c:2269
worker_thread+0xa0/0x800 kernel/workqueue.c:2415
kthread+0x1d4/0x200 drivers/block/aoe/aoecmd.c:1253
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:352

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 29572 Comm: kworker/1:4 Not tainted 5.4.0-rc6+ #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: events rt6_probe_deferred

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>
---
drivers/firewire/net.c | 6 +++++-
include/net/neighbour.h | 2 +-
net/core/neighbour.c | 4 ++--
net/ethernet/eth.c | 7 ++++++-
4 files changed, 14 insertions(+), 5 deletions(-)

diff --git a/drivers/firewire/net.c b/drivers/firewire/net.c
index 242359c2d1f1..215f4f71b943 100644
--- a/drivers/firewire/net.c
+++ b/drivers/firewire/net.c
@@ -249,7 +249,11 @@ static int fwnet_header_cache(const struct neighbour *neigh,
h = (struct fwnet_header *)((u8 *)hh->hh_data + HH_DATA_OFF(sizeof(*h)));
h->h_proto = type;
memcpy(h->h_dest, neigh->ha, net->addr_len);
- hh->hh_len = FWNET_HLEN;
+
+ /* Pairs with the READ_ONCE() in neigh_resolve_output(),
+ * neigh_hh_output() and neigh_update_hhs().
+ */
+ smp_store_release(&hh->hh_len, FWNET_HLEN);

return 0;
}
diff --git a/include/net/neighbour.h b/include/net/neighbour.h
index 1d6b98119a1d..e89273f9a0bc 100644
--- a/include/net/neighbour.h
+++ b/include/net/neighbour.h
@@ -458,7 +458,7 @@ static inline int neigh_hh_output(const struct hh_cache *hh, struct sk_buff *skb

do {
seq = read_seqbegin(&hh->hh_lock);
- hh_len = hh->hh_len;
+ hh_len = READ_ONCE(hh->hh_len);
if (likely(hh_len <= HH_DATA_MOD)) {
hh_alen = HH_DATA_MOD;

diff --git a/net/core/neighbour.c b/net/core/neighbour.c
index 2664ad58e5c0..16ac50b1b9a7 100644
--- a/net/core/neighbour.c
+++ b/net/core/neighbour.c
@@ -1094,7 +1094,7 @@ static void neigh_update_hhs(struct neighbour *neigh)

if (update) {
hh = &neigh->hh;
- if (hh->hh_len) {
+ if (READ_ONCE(hh->hh_len)) {
write_seqlock_bh(&hh->hh_lock);
update(hh, neigh->dev, neigh->ha);
write_sequnlock_bh(&hh->hh_lock);
@@ -1355,7 +1355,7 @@ int neigh_resolve_output(struct neighbour *neigh, struct sk_buff *skb)
struct net_device *dev = neigh->dev;
unsigned int seq;

- if (dev->header_ops->cache && !neigh->hh.hh_len)
+ if (dev->header_ops->cache && !READ_ONCE(neigh->hh.hh_len))
neigh_hh_init(neigh);

do {
diff --git a/net/ethernet/eth.c b/net/ethernet/eth.c
index eaeba9b99a73..7e0e5f2706ba 100644
--- a/net/ethernet/eth.c
+++ b/net/ethernet/eth.c
@@ -239,7 +239,12 @@ int eth_header_cache(const struct neighbour *neigh, struct hh_cache *hh, __be16
eth->h_proto = type;
memcpy(eth->h_source, dev->dev_addr, ETH_ALEN);
memcpy(eth->h_dest, neigh->ha, ETH_ALEN);
- hh->hh_len = ETH_HLEN;
+
+ /* Pairs with READ_ONCE() in neigh_resolve_output(),
+ * neigh_hh_output() and neigh_update_hhs().
+ */
+ smp_store_release(&hh->hh_len, ETH_HLEN);
+
return 0;
}
EXPORT_SYMBOL(eth_header_cache);
--
2.20.1


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