[PATCH 5.5 385/399] brd: check and limit max_part par

Greg Kroah-Hartman
2020-02-21T08:00:27Z

From: Zhiqiang Liu <liuzhiqiang26@huawei.com>

[ Upstream commit c8ab422553c81a0eb070329c63725df1cd1425bc ]

In brd_init func, rd_nr num of brd_device are firstly allocated
and add in brd_devices, then brd_devices are traversed to add each
brd_device by calling add_disk func. When allocating brd_device,
the disk->first_minor is set to i * max_part, if rd_nr * max_part
is larger than MINORMASK, two different brd_device may have the same
devt, then only one of them can be successfully added.
when rmmod brd.ko, it will cause oops when calling brd_exit.

Follow those steps:
# modprobe brd rd_nr=3 rd_size=102400 max_part=1048576
# rmmod brd
then, the oops will appear.

Oops log:
[ 726.613722] Call trace:
[ 726.614175] kernfs_find_ns+0x24/0x130
[ 726.614852] kernfs_find_and_get_ns+0x44/0x68
[ 726.615749] sysfs_remove_group+0x38/0xb0
[ 726.616520] blk_trace_remove_sysfs+0x1c/0x28
[ 726.617320] blk_unregister_queue+0x98/0x100
[ 726.618105] del_gendisk+0x144/0x2b8
[ 726.618759] brd_exit+0x68/0x560 [brd]
[ 726.619501] __arm64_sys_delete_module+0x19c/0x2a0
[ 726.620384] el0_svc_common+0x78/0x130
[ 726.621057] el0_svc_handler+0x38/0x78
[ 726.621738] el0_svc+0x8/0xc
[ 726.622259] Code: aa0203f6 aa0103f7 aa1e03e0 d503201f (7940e260)

Here, we add brd_check_and_reset_par func to check and limit max_part par.

--
V5->V6:
- remove useless code

V4->V5:(suggested by Ming Lei)
- make sure max_part is not larger than DISK_MAX_PARTS

V3->V4:(suggested by Ming Lei)
- remove useless change
- add one limit of max_part

V2->V3: (suggested by Ming Lei)
- clear .minors when running out of consecutive minor space in brd_alloc
- remove limit of rd_nr

V1->V2:
- add more checks in brd_check_par_valid as suggested by Ming Lei.

Signed-off-by: Zhiqiang Liu <liuzhiqiang26@huawei.com>
Reviewed-by: Bob Liu <bob.liu@oracle.com>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/block/brd.c | 22 ++++++++++++++++++++--
1 file changed, 20 insertions(+), 2 deletions(-)

diff --git a/drivers/block/brd.c b/drivers/block/brd.c
index a8730cc4db10e..220c5e18aba0c 100644
--- a/drivers/block/brd.c
+++ b/drivers/block/brd.c
@@ -473,6 +473,25 @@ static struct kobject *brd_probe(dev_t dev, int *part, void *data)
return kobj;
}

+static inline void brd_check_and_reset_par(void)
+{
+ if (unlikely(!max_part))
+ max_part = 1;
+
+ /*
+ * make sure 'max_part' can be divided exactly by (1U << MINORBITS),
+ * otherwise, it is possiable to get same dev_t when adding partitions.
+ */
+ if ((1U << MINORBITS) % max_part != 0)
+ max_part = 1UL << fls(max_part);
+
+ if (max_part > DISK_MAX_PARTS) {
+ pr_info("brd: max_part can't be larger than %d, reset max_part = %d.\n",
+ DISK_MAX_PARTS, DISK_MAX_PARTS);
+ max_part = DISK_MAX_PARTS;
+ }
+}
+
static int __init brd_init(void)
{
struct brd_device *brd, *next;
@@ -496,8 +515,7 @@ static int __init brd_init(void)
if (register_blkdev(RAMDISK_MAJOR, "ramdisk"))
return -EIO;

- if (unlikely(!max_part))
- max_part = 1;
+ brd_check_and_reset_par();

for (i = 0; i < rd_nr; i++) {
brd = brd_alloc(i);
--
2.20.1