Hi, 在 2023/06/05 20:28, Zhong Jinghua 写道:
From: Zhong Jinghua <zhongjinghua@xxxxxxxxxx> We found that in loop_control_ioctl, the kernel panic can be easily caused: 1. syscall(__NR_ioctl, r[1], 0x4c80, 0x80000200000ul); Create a loop device 0x80000200000ul. In fact, in the code, it is used as the first_minor number, and the first_minor number is 0. So the created loop device number is 7:0. 2. syscall(__NR_ioctl, r[2], 0x4c80, 0ul); Create a loop device 0x0ul. Since the 7:0 device has been created in 1, add_disk will fail because the major and first_minor numbers are consistent. 3. syscall(__NR_ioctl, r[5], 0x4c81, 0ul); Delete the device that failed to create, the kernel panics.
Please notice that kernel panic won't be triggered because add_disk() has appropriate error handling. Thanks, Kuai
Panic like below: BUG: KASAN: null-ptr-deref in device_del+0xb3/0x840 drivers/base/core.c:3107 Call Trace: kill_device drivers/base/core.c:3079 [inline] device_del+0xb3/0x840 drivers/base/core.c:3107 del_gendisk+0x463/0x5f0 block/genhd.c:971 loop_remove drivers/block/loop.c:2190 [inline] loop_control_ioctl drivers/block/loop.c:2289 [inline] The stack like below: Create loop device: loop_control_ioctl loop_add add_disk device_add_disk bdi_register bdi_register_va device_create device_create_groups_vargs device_add kfree(dev->p); dev->p = NULL; Remove loop device: loop_control_ioctl loop_remove del_gendisk device_del kill_device if (dev->p->dead) // p is null Fix it by adding a check for parm. Fixes: 770fe30a46a1 ("loop: add management interface for on-demand device allocation") Signed-off-by: Zhong Jinghua <zhongjinghua@xxxxxxxxxx> --- drivers/block/loop.c | 14 +++++++++++++- 1 file changed, 13 insertions(+), 1 deletion(-) diff --git a/drivers/block/loop.c b/drivers/block/loop.c index 76b96c42f417..60f2a31c4a24 100644 --- a/drivers/block/loop.c +++ b/drivers/block/loop.c @@ -2084,6 +2084,17 @@ static int loop_add(struct loop_device **l, int i) struct gendisk *disk; int err;+ /*+ * i << part_shift is actually used as the first_minor. + * So here should avoid i << part_shift overflow. + * And, MKDEV() expect that the max bits of + * first_minor is 20. + */ + if (i > 0 && i > MINORMASK >> part_shift) { + err = -EINVAL; + goto out; + } + err = -ENOMEM; lo = kzalloc(sizeof(*lo), GFP_KERNEL); if (!lo) @@ -2097,7 +2108,8 @@ static int loop_add(struct loop_device **l, int i) if (err == -ENOSPC) err = -EEXIST; } else { - err = idr_alloc(&loop_index_idr, lo, 0, 0, GFP_KERNEL); + err = idr_alloc(&loop_index_idr, lo, 0, + (MINORMASK >> part_shift) + 1, GFP_KERNEL); } if (err < 0) goto out_free_dev;
