[PATCH 6.4 212/800] sfc: fix crash when reading stats while NIC is resetting

Greg Kroah-Hartman
2023-07-16T20:04:09Z

From: Edward Cree <ecree.xilinx@gmail.com>

[ Upstream commit d1b355438b8325a486f087e506d412c4e852f37b ]

efx_net_stats() (.ndo_get_stats64) can be called during an ethtool
selftest, during which time nic_data->mc_stats is NULL as the NIC has
been fini'd. In this case do not attempt to fetch the latest stats
from the hardware, else we will crash on a NULL dereference:
BUG: kernel NULL pointer dereference, address: 0000000000000038
RIP efx_nic_update_stats
abridged calltrace:
efx_ef10_update_stats_pf
efx_net_stats
dev_get_stats
dev_seq_printf_stats
Skipping the read is safe, we will simply give out stale stats.
To ensure that the free in efx_ef10_fini_nic() does not race against
efx_ef10_update_stats_pf(), which could cause a TOCTTOU bug, take the
efx->stats_lock in fini_nic (it is already held across update_stats).

Fixes: d3142c193dca ("sfc: refactor EF10 stats handling")
Reviewed-by: Pieter Jansen van Vuuren <pieter.jansen-van-vuuren@amd.com>
Signed-off-by: Edward Cree <ecree.xilinx@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/net/ethernet/sfc/ef10.c | 13 ++++++++++---
1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/drivers/net/ethernet/sfc/ef10.c b/drivers/net/ethernet/sfc/ef10.c
index b63e47af63655..8c019f382a7f3 100644
--- a/drivers/net/ethernet/sfc/ef10.c
+++ b/drivers/net/ethernet/sfc/ef10.c
@@ -1297,8 +1297,10 @@ static void efx_ef10_fini_nic(struct efx_nic *efx)
{
struct efx_ef10_nic_data *nic_data = efx->nic_data;

+ spin_lock_bh(&efx->stats_lock);
kfree(nic_data->mc_stats);
nic_data->mc_stats = NULL;
+ spin_unlock_bh(&efx->stats_lock);
}

static int efx_ef10_init_nic(struct efx_nic *efx)
@@ -1852,9 +1854,14 @@ static size_t efx_ef10_update_stats_pf(struct efx_nic *efx, u64 *full_stats,

efx_ef10_get_stat_mask(efx, mask);

- efx_nic_copy_stats(efx, nic_data->mc_stats);
- efx_nic_update_stats(efx_ef10_stat_desc, EF10_STAT_COUNT,
- mask, stats, nic_data->mc_stats, false);
+ /* If NIC was fini'd (probably resetting), then we can't read
+ * updated stats right now.
+ */
+ if (nic_data->mc_stats) {
+ efx_nic_copy_stats(efx, nic_data->mc_stats);
+ efx_nic_update_stats(efx_ef10_stat_desc, EF10_STAT_COUNT,
+ mask, stats, nic_data->mc_stats, false);
+ }

/* Update derived statistics */
efx_nic_fix_nodesc_drop_stat(efx,
--
2.39.2