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    Subject[PATCH AUTOSEL 5.5 528/542] brd: check and limit max_part par
    Date
    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
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