Jason has been running Syzkaller that reported the following bug: sysfs: cannot create duplicate filename '/devices/iommufd_mock4'
Call Trace: sysfs_warn_dup+0x71/0x90 sysfs_create_dir_ns+0x1ee/0x260 ? sysfs_create_mount_point+0x80/0x80 ? spin_bug+0x1d0/0x1d0 ? do_raw_spin_unlock+0x54/0x220 kobject_add_internal+0x221/0x970 kobject_add+0x11c/0x1e0 ? lockdep_hardirqs_on_prepare+0x273/0x3e0 ? kset_create_and_add+0x160/0x160 ? kobject_put+0x5d/0x390 ? bus_get_dev_root+0x4a/0x60 ? kobject_put+0x5d/0x390 device_add+0x1d5/0x1550 ? __fw_devlink_link_to_consumers.isra.0+0x1f0/0x1f0 ? __init_waitqueue_head+0xcb/0x150 iommufd_test+0x462/0x3b60 ? lock_release+0x1fe/0x640 ? __might_fault+0x117/0x170 ? reacquire_held_locks+0x4b0/0x4b0 ? iommufd_selftest_destroy+0xd0/0xd0 ? __might_fault+0xbe/0x170 iommufd_fops_ioctl+0x256/0x350 ? iommufd_option+0x180/0x180 ? __lock_acquire+0x1755/0x45f0 __x64_sys_ioctl+0xa13/0x1640
The bug is triggered when Syzkaller created multiple mock devices but didn't destroy them in the same sequence, messing up the mock_dev_num counter. So, fix it with a mock_dev_ida.
Fixes: 23a1b46f15d5 ("iommufd/selftest: Make the mock iommu driver into a real driver") Cc: stable@vger.kernel.org Reported-by: Jason Gunthorpe jgg@nvidia.com Signed-off-by: Nicolin Chen nicolinc@nvidia.com --- drivers/iommu/iommufd/selftest.c | 13 +++++++++---- 1 file changed, 9 insertions(+), 4 deletions(-)
diff --git a/drivers/iommu/iommufd/selftest.c b/drivers/iommu/iommufd/selftest.c index 8abf9747773e..2bfe77bd351d 100644 --- a/drivers/iommu/iommufd/selftest.c +++ b/drivers/iommu/iommufd/selftest.c @@ -36,7 +36,7 @@ static struct mock_bus_type iommufd_mock_bus_type = { }, };
-static atomic_t mock_dev_num; +static DEFINE_IDA(mock_dev_ida);
enum { MOCK_DIRTY_TRACK = 1, @@ -123,6 +123,7 @@ enum selftest_obj_type { struct mock_dev { struct device dev; unsigned long flags; + int id; };
struct selftest_obj { @@ -631,7 +632,7 @@ static void mock_dev_release(struct device *dev) { struct mock_dev *mdev = container_of(dev, struct mock_dev, dev);
- atomic_dec(&mock_dev_num); + ida_free(&mock_dev_ida, mdev->id); kfree(mdev); }
@@ -653,8 +654,12 @@ static struct mock_dev *mock_dev_create(unsigned long dev_flags) mdev->dev.release = mock_dev_release; mdev->dev.bus = &iommufd_mock_bus_type.bus;
- rc = dev_set_name(&mdev->dev, "iommufd_mock%u", - atomic_inc_return(&mock_dev_num)); + rc = ida_alloc(&mock_dev_ida, GFP_KERNEL); + if (rc < 0) + goto err_put; + mdev->id = rc; + + rc = dev_set_name(&mdev->dev, "iommufd_mock%u", mdev->id); if (rc) goto err_put;