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Subject[PATCH V3] brd: check and limit max_part par
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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.

--
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>
---
drivers/block/brd.c | 35 ++++++++++++++++++++++++++++-------
1 file changed, 28 insertions(+), 7 deletions(-)

diff --git a/drivers/block/brd.c b/drivers/block/brd.c
index df8103dd40ac..2295a0bafb5e 100644
--- a/drivers/block/brd.c
+++ b/drivers/block/brd.c
@@ -330,16 +330,16 @@ static const struct block_device_operations brd_fops = {
/*
* And now the modules code and kernel interface.
*/
-static int rd_nr = CONFIG_BLK_DEV_RAM_COUNT;
-module_param(rd_nr, int, 0444);
+static unsigned int rd_nr = CONFIG_BLK_DEV_RAM_COUNT;
+module_param(rd_nr, uint, 0444);
MODULE_PARM_DESC(rd_nr, "Maximum number of brd devices");

unsigned long rd_size = CONFIG_BLK_DEV_RAM_SIZE;
module_param(rd_size, ulong, 0444);
MODULE_PARM_DESC(rd_size, "Size of each RAM disk in kbytes.");

-static int max_part = 1;
-module_param(max_part, int, 0444);
+static unsigned int max_part = 1;
+module_param(max_part, uint, 0444);
MODULE_PARM_DESC(max_part, "Num Minors to reserve between devices");

MODULE_LICENSE("GPL");
@@ -393,7 +393,14 @@ static struct brd_device *brd_alloc(int i)
if (!disk)
goto out_free_queue;
disk->major = RAMDISK_MAJOR;
- disk->first_minor = i * max_part;
+ /*
+ * Clear .minors when running out of consecutive minor space since
+ * GENHD_FL_EXT_DEVT is set, and we can allocate from extended devt.
+ */
+ if ((i * disk->minors) & ~MINORMASK)
+ disk->minors = 0;
+ else
+ disk->first_minor = i * disk->minors;
disk->fops = &brd_fops;
disk->private_data = brd;
disk->queue = brd->brd_queue;
@@ -468,6 +475,21 @@ 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(!rd_nr))
+ rd_nr = 1;
+
+ if (unlikely(!max_part))
+ max_part = 1;
+
+ 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;
@@ -491,8 +513,7 @@ 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);
--
2.19.1

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