[PATCH] loop: fix to a race condition due to the early registration of device

[Anton Volkov]

The early device registration made possible a race leading to allocations
of disks with wrong minors.

This patch moves the device registration further down the loop_init
function to make the race infeasible.

Found by Linux Driver Verification project (linuxtesting.org).

Signed-off-by: Anton Volkov <avol...@ispras.ru>
Reviewed-by: Ming Lei <ming....@redhat.com>
---
 drivers/block/loop.c | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index ef83349..2fbd4089 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -1996,10 +1996,6 @@ static int __init loop_init(void)
        struct loop_device *lo;
        int err;
 
-       err = misc_register(&loop_misc);
-       if (err < 0)
-               return err;
-
        part_shift = 0;
        if (max_part > 0) {
                part_shift = fls(max_part);
@@ -2017,12 +2013,12 @@ static int __init loop_init(void)
 
        if ((1UL << part_shift) > DISK_MAX_PARTS) {
                err = -EINVAL;
-               goto misc_out;
+               goto err_out;
        }
 
        if (max_loop > 1UL << (MINORBITS - part_shift)) {
                err = -EINVAL;
-               goto misc_out;
+               goto err_out;
        }
 
        /*
@@ -2041,6 +2037,11 @@ static int __init loop_init(void)
                range = 1UL << MINORBITS;
        }
 
+       err = misc_register(&loop_misc);
+       if (err < 0)
+               goto err_out;
+
+
        if (register_blkdev(LOOP_MAJOR, "loop")) {
                err = -EIO;
                goto misc_out;
@@ -2060,6 +2061,7 @@ static int __init loop_init(void)
 
 misc_out:
        misc_deregister(&loop_misc);
+err_out:
        return err;
 }
 
-- 
2.7.4