driver core: Fix unbalanced device reference in drivers_probe

bus_find_device_by_name() acquires a device reference which is never
released.  This results in an object leak, which on older kernels
results in failure to release all resources of PCI devices.  libvirt
uses drivers_probe to re-attach devices to the host after assignment
and is therefore a common trigger for this leak.

Example:

# cd /sys/bus/pci/
# dmesg -C
# echo 1 > devices/0000\:01\:00.0/sriov_numvfs
# echo 0 > devices/0000\:01\:00.0/sriov_numvfs
# dmesg | grep 01:10
 pci 0000:01:10.0: [8086:10ca] type 00 class 0x020000
 kobject: '0000:01:10.0' (ffff8801d79cd0a8): kobject_add_internal: parent: '0000:00:01.0', set: 'devices'
 kobject: '0000:01:10.0' (ffff8801d79cd0a8): kobject_uevent_env
 kobject: '0000:01:10.0' (ffff8801d79cd0a8): fill_kobj_path: path = '/devices/pci0000:00/0000:00:01.0/0000:01:10.0'
 kobject: '0000:01:10.0' (ffff8801d79cd0a8): kobject_uevent_env
 kobject: '0000:01:10.0' (ffff8801d79cd0a8): fill_kobj_path: path = '/devices/pci0000:00/0000:00:01.0/0000:01:10.0'
 kobject: '0000:01:10.0' (ffff8801d79cd0a8): kobject_uevent_env
 kobject: '0000:01:10.0' (ffff8801d79cd0a8): fill_kobj_path: path = '/devices/pci0000:00/0000:00:01.0/0000:01:10.0'
 kobject: '0000:01:10.0' (ffff8801d79cd0a8): kobject_cleanup, parent           (null)
 kobject: '0000:01:10.0' (ffff8801d79cd0a8): calling ktype release
 kobject: '0000:01:10.0': free name

[kobject freed as expected]

# dmesg -C
# echo 1 > devices/0000\:01\:00.0/sriov_numvfs
# echo 0000:01:10.0 > drivers_probe
# echo 0 > devices/0000\:01\:00.0/sriov_numvfs
# dmesg | grep 01:10
 pci 0000:01:10.0: [8086:10ca] type 00 class 0x020000
 kobject: '0000:01:10.0' (ffff8801d79ce0a8): kobject_add_internal: parent: '0000:00:01.0', set: 'devices'
 kobject: '0000:01:10.0' (ffff8801d79ce0a8): kobject_uevent_env
 kobject: '0000:01:10.0' (ffff8801d79ce0a8): fill_kobj_path: path = '/devices/pci0000:00/0000:00:01.0/0000:01:10.0'
 kobject: '0000:01:10.0' (ffff8801d79ce0a8): kobject_uevent_env
 kobject: '0000:01:10.0' (ffff8801d79ce0a8): fill_kobj_path: path = '/devices/pci0000:00/0000:00:01.0/0000:01:10.0'
 kobject: '0000:01:10.0' (ffff8801d79ce0a8): kobject_uevent_env
 kobject: '0000:01:10.0' (ffff8801d79ce0a8): fill_kobj_path: path = '/devices/pci0000:00/0000:00:01.0/0000:01:10.0'

[no free]

Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
Cc: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 5 insertions, 3 deletions

diff --git a/drivers/base/bus.c b/drivers/base/bus.c
index 83e910a57563..876bae5ade33 100644
--- a/drivers/base/bus.c
+++ b/drivers/base/bus.c
@@ -254,13 +254,15 @@ static ssize_t store_drivers_probe(struct bus_type *bus,
                                    const char *buf, size_t count)
 {
         struct device *dev;
+        int err = -EINVAL;
 
         dev = bus_find_device_by_name(bus, NULL, buf);
         if (!dev)
                 return -ENODEV;
-        if (bus_rescan_devices_helper(dev, NULL) != 0)
-                return -EINVAL;
-        return count;
+        if (bus_rescan_devices_helper(dev, NULL) == 0)
+                err = count;
+        put_device(dev);
+        return err;
 }
 
 static struct device *next_device(struct klist_iter *i)