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Subject[PATCH -next] ubi: fix race between ctrl_cdev_ioctl and ubi_cdev_ioctl
Date
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 following race could cause the use-after-free problem:
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

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. However, volume addition and deletion operations are performed
in both ctrl_cdev_ioctl and ubi_cdev_ioctl. When these operations are
performed concurrently in both ioctl, a race condition may be triggered.The
UAF stack above is one such case.

To solve this problem, add spin_lock(&ubi->volumes_lock) to ctrl_cdev_ioctl
where volumes are added and deleted.

Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Baokun Li <libaokun1@huawei.com>
---
drivers/mtd/ubi/build.c | 3 +++
1 file changed, 3 insertions(+)

diff --git a/drivers/mtd/ubi/build.c b/drivers/mtd/ubi/build.c
index a7e3eb9befb6..708b1b96de01 100644
--- a/drivers/mtd/ubi/build.c
+++ b/drivers/mtd/ubi/build.c
@@ -467,6 +467,7 @@ static int uif_init(struct ubi_device *ubi)
if (err)
goto out_unreg;

+ spin_lock(&ubi->volumes_lock);
for (i = 0; i < ubi->vtbl_slots; i++)
if (ubi->volumes[i]) {
err = ubi_add_volume(ubi, ubi->volumes[i]);
@@ -475,11 +476,13 @@ static int uif_init(struct ubi_device *ubi)
goto out_volumes;
}
}
+ spin_unlock(&ubi->volumes_lock);

return 0;

out_volumes:
kill_volumes(ubi);
+ spin_unlock(&ubi->volumes_lock);
cdev_device_del(&ubi->cdev, &ubi->dev);
out_unreg:
unregister_chrdev_region(ubi->cdev.dev, ubi->vtbl_slots + 1);
--
2.31.1
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