[PATCH AUTOSEL 6.6 15/21] netpoll: Fix race condition in netpoll_owner_active

Sasha Levin
2024-05-27T14:16:35Z

From: Breno Leitao <leitao@debian.org>

[ Upstream commit c2e6a872bde9912f1a7579639c5ca3adf1003916 ]

KCSAN detected a race condition in netpoll:

BUG: KCSAN: data-race in net_rx_action / netpoll_send_skb
write (marked) to 0xffff8881164168b0 of 4 bytes by interrupt on cpu 10:
net_rx_action (./include/linux/netpoll.h:90 net/core/dev.c:6712 net/core/dev.c:6822)
<snip>
read to 0xffff8881164168b0 of 4 bytes by task 1 on cpu 2:
netpoll_send_skb (net/core/netpoll.c:319 net/core/netpoll.c:345 net/core/netpoll.c:393)
netpoll_send_udp (net/core/netpoll.c:?)
<snip>
value changed: 0x0000000a -> 0xffffffff

This happens because netpoll_owner_active() needs to check if the
current CPU is the owner of the lock, touching napi->poll_owner
non atomically. The ->poll_owner field contains the current CPU holding
the lock.

Use an atomic read to check if the poll owner is the current CPU.

Signed-off-by: Breno Leitao <leitao@debian.org>
Link: https://lore.kernel.org/r/20240429100437.3487432-1-leitao@debian.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/core/netpoll.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/core/netpoll.c b/net/core/netpoll.c
index 543007f159f99..55bcacf67df3b 100644
--- a/net/core/netpoll.c
+++ b/net/core/netpoll.c
@@ -316,7 +316,7 @@ static int netpoll_owner_active(struct net_device *dev)
struct napi_struct *napi;

list_for_each_entry_rcu(napi, &dev->napi_list, dev_list) {
- if (napi->poll_owner == smp_processor_id())
+ if (READ_ONCE(napi->poll_owner) == smp_processor_id())
return 1;
}
return 0;
--
2.43.0