[PATCH net 1/3] net/mlx5e: SD, Fix race condition in secondary device probe/remove

[Tariq Toukan <tariqt@nvidia.com>]

From: Shay Drory <shayd@nvidia.com>

When utilizing Socket-Direct single netdev functionality the driver
resolves the actual auxiliary device using mlx5_sd_get_adev(). However,
the current implementation returns the primary ETH auxiliary device
without holding the device lock, leading to a potential race condition
where the ETH device could be unbound or removed concurrently during
probe, suspend, resume, or remove operations.[1]

Fix this by introducing mlx5_sd_put_adev() and updating
mlx5_sd_get_adev() so that secondaries devices would acquire the device
lock of the returned auxiliary device. After the lock is acquired, a
second devcom check is needed[2].
In addition, update The callers to pair the get operation with the new
put operation, ensuring the lock is held while the auxiliary device is
being operated on and released afterwards.

[1]
for example:
BUG: kernel NULL pointer dereference, address: 0000000000000370
PGD 0 P4D 0
Oops: Oops: 0000 [#1] SMP
CPU: 4 UID: 0 PID: 3945 Comm: bash Not tainted 6.19.0-rc3+ #1 NONE
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.13.0-0-gf21b5a4aeb02-prebuilt.qemu.org 04/01/2014
RIP: 0010:mlx5e_dcbnl_dscp_app+0x23/0x100 [mlx5_core]
Call Trace:
 <TASK>
 mlx5e_remove+0x82/0x12a [mlx5_core]
 device_release_driver_internal+0x194/0x1f0
 bus_remove_device+0xc6/0x140
 device_del+0x159/0x3c0
 ? devl_param_driverinit_value_get+0x29/0x80
 mlx5_rescan_drivers_locked+0x92/0x160 [mlx5_core]
 mlx5_unregister_device+0x34/0x50 [mlx5_core]
 mlx5_uninit_one+0x43/0xb0 [mlx5_core]
 remove_one+0x4e/0xc0 [mlx5_core]
 pci_device_remove+0x39/0xa0
 device_release_driver_internal+0x194/0x1f0
 unbind_store+0x99/0xa0
 kernfs_fop_write_iter+0x12e/0x1e0
 vfs_write+0x215/0x3d0
 ksys_write+0x5f/0xd0
 do_syscall_64+0x55/0xe90
 entry_SYSCALL_64_after_hwframe+0x4b/0x53

[2]
    CPU0 (primary)                     CPU1 (secondary)
==========================================================================
mlx5e_remove() (device_lock held)
                                     mlx5e_remove() (2nd device_lock held)
                                      mlx5_sd_get_adev()
                                       mlx5_devcom_comp_is_ready() => true
                                       device_lock(primary)
 mlx5_sd_get_adev() ==> ret adev
 _mlx5e_remove()
 mlx5_sd_cleanup()
 // mlx5e_remove finished
 // releasing device_lock
                                       //need another check here...
                                       mlx5_devcom_comp_is_ready() => false

Fixes: 381978d28317 ("net/mlx5e: Create single netdev per SD group")
Signed-off-by: Shay Drory <shayd@nvidia.com>
Signed-off-by: Tariq Toukan <tariqt@nvidia.com>
---
 .../net/ethernet/mellanox/mlx5/core/en_main.c  | 18 ++++++++++++++----
 .../net/ethernet/mellanox/mlx5/core/lib/sd.c   | 13 +++++++++++++
 .../net/ethernet/mellanox/mlx5/core/lib/sd.h   |  2 ++
 3 files changed, 29 insertions(+), 4 deletions(-)

diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en_main.c b/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
index b6c12460b54a..5761f655f488 100644
--- a/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
+++ b/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
@@ -6657,8 +6657,11 @@ static int mlx5e_resume(struct auxiliary_device *adev)
 		return err;
 
 	actual_adev = mlx5_sd_get_adev(mdev, adev, edev->idx);
-	if (actual_adev)
-		return _mlx5e_resume(actual_adev);
+	if (actual_adev) {
+		err = _mlx5e_resume(actual_adev);
+		mlx5_sd_put_adev(actual_adev, adev);
+		return err;
+	}
 	return 0;
 }
 
@@ -6698,6 +6701,8 @@ static int mlx5e_suspend(struct auxiliary_device *adev, pm_message_t state)
 		err = _mlx5e_suspend(actual_adev, false);
 
 	mlx5_sd_cleanup(mdev);
+	if (actual_adev)
+		mlx5_sd_put_adev(actual_adev, adev);
 	return err;
 }
 
@@ -6787,8 +6792,11 @@ static int mlx5e_probe(struct auxiliary_device *adev,
 		return err;
 
 	actual_adev = mlx5_sd_get_adev(mdev, adev, edev->idx);
-	if (actual_adev)
-		return _mlx5e_probe(actual_adev);
+	if (actual_adev) {
+		err = _mlx5e_probe(actual_adev);
+		mlx5_sd_put_adev(actual_adev, adev);
+		return err;
+	}
 	return 0;
 }
 
@@ -6841,6 +6849,8 @@ static void mlx5e_remove(struct auxiliary_device *adev)
 		_mlx5e_remove(actual_adev);
 
 	mlx5_sd_cleanup(mdev);
+	if (actual_adev)
+		mlx5_sd_put_adev(actual_adev, adev);
 }
 
 static const struct auxiliary_device_id mlx5e_id_table[] = {
diff --git a/drivers/net/ethernet/mellanox/mlx5/core/lib/sd.c b/drivers/net/ethernet/mellanox/mlx5/core/lib/sd.c
index 954942ad93c5..060649645012 100644
--- a/drivers/net/ethernet/mellanox/mlx5/core/lib/sd.c
+++ b/drivers/net/ethernet/mellanox/mlx5/core/lib/sd.c
@@ -528,5 +528,18 @@ struct auxiliary_device *mlx5_sd_get_adev(struct mlx5_core_dev *dev,
 	if (dev == primary)
 		return adev;
 
+	device_lock(&primary->priv.adev[idx]->adev.dev);
+	/* In case primary finish removing its adev */
+	if (!mlx5_devcom_comp_is_ready(sd->devcom)) {
+		device_unlock(&primary->priv.adev[idx]->adev.dev);
+		return NULL;
+	}
 	return &primary->priv.adev[idx]->adev;
 }
+
+void mlx5_sd_put_adev(struct auxiliary_device *actual_adev,
+		      struct auxiliary_device *adev)
+{
+	if (actual_adev != adev)
+		device_unlock(&actual_adev->dev);
+}
diff --git a/drivers/net/ethernet/mellanox/mlx5/core/lib/sd.h b/drivers/net/ethernet/mellanox/mlx5/core/lib/sd.h
index 137efaf9aabc..9bfd5b9756b5 100644
--- a/drivers/net/ethernet/mellanox/mlx5/core/lib/sd.h
+++ b/drivers/net/ethernet/mellanox/mlx5/core/lib/sd.h
@@ -15,6 +15,8 @@ struct mlx5_core_dev *mlx5_sd_ch_ix_get_dev(struct mlx5_core_dev *primary, int c
 struct auxiliary_device *mlx5_sd_get_adev(struct mlx5_core_dev *dev,
 					  struct auxiliary_device *adev,
 					  int idx);
+void mlx5_sd_put_adev(struct auxiliary_device *actual_adev,
+		      struct auxiliary_device *adev);
 
 int mlx5_sd_init(struct mlx5_core_dev *dev);
 void mlx5_sd_cleanup(struct mlx5_core_dev *dev);
-- 
2.44.0