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md: avoid repeated calls to del_gendisk

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There is a uaf problem which is found by case 23rdev-lifetime:

Oops: general protection fault, probably for non-canonical address 0xdead000000000122
RIP: 0010:bdi_unregister+0x4b/0x170
Call Trace:
 <TASK>
 __del_gendisk+0x356/0x3e0
 mddev_unlock+0x351/0x360
 rdev_attr_store+0x217/0x280
 kernfs_fop_write_iter+0x14a/0x210
 vfs_write+0x29e/0x550
 ksys_write+0x74/0xf0
 do_syscall_64+0xbb/0x380
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7ff5250a177e

The sequence is:
1. rdev remove path gets reconfig_mutex
2. rdev remove path release reconfig_mutex in mddev_unlock
3. md stop calls do_md_stop and sets MD_DELETED
4. rdev remove path calls del_gendisk because MD_DELETED is set
5. md stop path release reconfig_mutex and calls del_gendisk again

So there is a race condition we should resolve. This patch adds a
flag MD_DO_DELETE to avoid the race condition.

Link: https://lore.kernel.org/linux-raid/20251029063419.21700-1-xni@redhat.com
Fixes: 9e59d60976 ("md: call del_gendisk in control path")
Signed-off-by: Xiao Ni <xni@redhat.com>
Suggested-by: Yu Kuai <yukuai@fnnas.com>
Reviewed-by: Li Nan <linan122@huawei.com>
Signed-off-by: Yu Kuai <yukuai@fnnas.com>
This commit is contained in:
Xiao Ni 2025-10-29 14:34:19 +08:00 committed by Yu Kuai
parent 46caa40534
commit 90e3bb44c0
2 changed files with 3 additions and 1 deletions
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3
drivers/md/md.c
View File

@ -941,7 +941,8 @@ void mddev_unlock(struct mddev *mddev)
* do_md_stop. dm raid only uses md_stop to stop. So dm raid
* doesn't need to check MD_DELETED when getting reconfig lock
*/
if (test_bit(MD_DELETED, &mddev->flags)) {
if (test_bit(MD_DELETED, &mddev->flags) &&
!test_and_set_bit(MD_DO_DELETE, &mddev->flags)) {
kobject_del(&mddev->kobj);
del_gendisk(mddev->gendisk);
}

1
drivers/md/md.h
View File

@ -354,6 +354,7 @@ enum mddev_flags {
MD_HAS_MULTIPLE_PPLS,
MD_NOT_READY,
MD_BROKEN,
MD_DO_DELETE,
MD_DELETED,
};