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SubjectRe: [PATCH -next V3] ubi: fix race condition between ctrl_cdev_ioctl and ubi_cdev_ioctl
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在 2021/11/5 17:30, Baokun Li 写道:

ping

> Hulk Robot reported a KASAN report about use-after-free:
> ==================================================================
> BUG: KASAN: use-after-free in __list_del_entry_valid+0x13d/0x160
> Read of size 8 at addr ffff888035e37d98 by task ubiattach/1385
> [...]
> Call Trace:
> klist_dec_and_del+0xa7/0x4a0
> klist_put+0xc7/0x1a0
> device_del+0x4d4/0xed0
> cdev_device_del+0x1a/0x80
> ubi_attach_mtd_dev+0x2951/0x34b0 [ubi]
> ctrl_cdev_ioctl+0x286/0x2f0 [ubi]
>
> Allocated by task 1414:
> device_add+0x60a/0x18b0
> cdev_device_add+0x103/0x170
> ubi_create_volume+0x1118/0x1a10 [ubi]
> ubi_cdev_ioctl+0xb7f/0x1ba0 [ubi]
>
> Freed by task 1385:
> cdev_device_del+0x1a/0x80
> ubi_remove_volume+0x438/0x6c0 [ubi]
> ubi_cdev_ioctl+0xbf4/0x1ba0 [ubi]
> [...]
> ==================================================================
>
> The lock held by ctrl_cdev_ioctl is ubi_devices_mutex, but the lock held
> by ubi_cdev_ioctl is ubi->device_mutex. Therefore, the two locks can be
> concurrent.
>
> ctrl_cdev_ioctl contains two operations: ubi_attach and ubi_detach.
> ubi_detach is bug-free because it uses reference counting to prevent
> concurrency. However, uif_init and uif_close in ubi_attach may race with
> ubi_cdev_ioctl.
>
> uif_init will race with ubi_cdev_ioctl as in the following stack.
> cpu1 cpu2 cpu3
> _______________________|________________________|______________________
> ctrl_cdev_ioctl
> ubi_attach_mtd_dev
> uif_init
> ubi_cdev_ioctl
> ubi_create_volume
> cdev_device_add
> ubi_add_volume
> // sysfs exist
> kill_volumes
> ubi_cdev_ioctl
> ubi_remove_volume
> cdev_device_del
> // first free
> ubi_free_volume
> cdev_del
> // double free
> cdev_device_del
>
> And uif_close will race with ubi_cdev_ioctl as in the following stack.
> cpu1 cpu2 cpu3
> _______________________|________________________|______________________
> ctrl_cdev_ioctl
> ubi_attach_mtd_dev
> uif_init
> ubi_cdev_ioctl
> ubi_create_volume
> cdev_device_add
> ubi_debugfs_init_dev
> //error goto out_uif;
> uif_close
> kill_volumes
> ubi_cdev_ioctl
> ubi_remove_volume
> cdev_device_del
> // first free
> ubi_free_volume
> // double free
>
> The cause of this problem is that commit 714fb87e8bc0 make device
> "available" before it becomes accessible via sysfs. Therefore, we
> roll back the modification. We will fix the race condition between
> ubi device creation and udev by removing ubi_get_device in
> vol_attribute_show and dev_attribute_show.This avoids accessing
> uninitialized ubi_devices[ubi_num].
>
> ubi_get_device is used to prevent devices from being deleted during
> sysfs execution. However, now kernfs ensures that devices will not
> be deleted before all reference counting are released.
> The key process is shown in the following stack.
>
> device_del
> device_remove_attrs
> device_remove_groups
> sysfs_remove_groups
> sysfs_remove_group
> remove_files
> kernfs_remove_by_name
> kernfs_remove_by_name_ns
> __kernfs_remove
> kernfs_drain
>
> Fixes: 714fb87e8bc0 ("ubi: Fix race condition between ubi device creation and udev")
> Reported-by: Hulk Robot <hulkci@huawei.com>
> Signed-off-by: Baokun Li <libaokun1@huawei.com>
> ---
> V1->V2:
> Add race in uif_close
> V2->V3:
> Solution modified becase ubi_add_volume might sleepping in spin_lock.
>
> drivers/mtd/ubi/build.c | 9 +--------
> drivers/mtd/ubi/vmt.c | 8 +-------
> 2 files changed, 2 insertions(+), 15 deletions(-)
>
> diff --git a/drivers/mtd/ubi/build.c b/drivers/mtd/ubi/build.c
> index a7e3eb9befb6..a32050fecabf 100644
> --- a/drivers/mtd/ubi/build.c
> +++ b/drivers/mtd/ubi/build.c
> @@ -351,9 +351,6 @@ static ssize_t dev_attribute_show(struct device *dev,
> * we still can use 'ubi->ubi_num'.
> */
> ubi = container_of(dev, struct ubi_device, dev);
> - ubi = ubi_get_device(ubi->ubi_num);
> - if (!ubi)
> - return -ENODEV;
>
> if (attr == &dev_eraseblock_size)
> ret = sprintf(buf, "%d\n", ubi->leb_size);
> @@ -382,7 +379,6 @@ static ssize_t dev_attribute_show(struct device *dev,
> else
> ret = -EINVAL;
>
> - ubi_put_device(ubi);
> return ret;
> }
>
> @@ -979,9 +975,6 @@ int ubi_attach_mtd_dev(struct mtd_info *mtd, int ubi_num,
> goto out_detach;
> }
>
> - /* Make device "available" before it becomes accessible via sysfs */
> - ubi_devices[ubi_num] = ubi;
> -
> err = uif_init(ubi);
> if (err)
> goto out_detach;
> @@ -1026,6 +1019,7 @@ int ubi_attach_mtd_dev(struct mtd_info *mtd, int ubi_num,
> wake_up_process(ubi->bgt_thread);
> spin_unlock(&ubi->wl_lock);
>
> + ubi_devices[ubi_num] = ubi;
> ubi_notify_all(ubi, UBI_VOLUME_ADDED, NULL);
> return ubi_num;
>
> @@ -1034,7 +1028,6 @@ int ubi_attach_mtd_dev(struct mtd_info *mtd, int ubi_num,
> out_uif:
> uif_close(ubi);
> out_detach:
> - ubi_devices[ubi_num] = NULL;
> ubi_wl_close(ubi);
> ubi_free_all_volumes(ubi);
> vfree(ubi->vtbl);
> diff --git a/drivers/mtd/ubi/vmt.c b/drivers/mtd/ubi/vmt.c
> index 139ee132bfbc..1bc7b3a05604 100644
> --- a/drivers/mtd/ubi/vmt.c
> +++ b/drivers/mtd/ubi/vmt.c
> @@ -56,16 +56,11 @@ static ssize_t vol_attribute_show(struct device *dev,
> {
> int ret;
> struct ubi_volume *vol = container_of(dev, struct ubi_volume, dev);
> - struct ubi_device *ubi;
> -
> - ubi = ubi_get_device(vol->ubi->ubi_num);
> - if (!ubi)
> - return -ENODEV;
> + struct ubi_device *ubi = vol->ubi;
>
> spin_lock(&ubi->volumes_lock);
> if (!ubi->volumes[vol->vol_id]) {
> spin_unlock(&ubi->volumes_lock);
> - ubi_put_device(ubi);
> return -ENODEV;
> }
> /* Take a reference to prevent volume removal */
> @@ -103,7 +98,6 @@ static ssize_t vol_attribute_show(struct device *dev,
> vol->ref_count -= 1;
> ubi_assert(vol->ref_count >= 0);
> spin_unlock(&ubi->volumes_lock);
> - ubi_put_device(ubi);
> return ret;
> }
>


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