Messages in this thread Patch in this message |  | | From | Baokun Li <> | Subject | [PATCH -next] ubi: fix race between ctrl_cdev_ioctl and ubi_cdev_ioctl | Date | Mon, 1 Nov 2021 09:37:39 +0800 |
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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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