CVE-2024-38598: md: fix resync softlockup when bitmap size is less than array size

In the Linux kernel, the following vulnerability has been resolved:

md: fix resync softlockup when bitmap size is less than array size

Is is reported that for dm-raid10, lvextend + lvchange --syncaction will trigger following softlockup:

kernel:watchdog: BUG: soft lockup - CPU#3 stuck for 26s! [mdXresync:6976] CPU: 7 PID: 3588 Comm: mdXresync Kdump: loaded Not tainted 6.9.0-rc4-next-20240419 #1 RIP: 0010:rawspinunlockirq+0x13/0x30 Call Trace: <TASK> mdbitmapstartsync+0x6b/0xf0 raid10syncrequest+0x25c/0x1b40 [raid10] mddosync+0x64b/0x1020 mdthread+0xa7/0x170 kthread+0xcf/0x100 retfromfork+0x30/0x50 retfromforkasm+0x1a/0x30

And the detailed process is as follows:

mddosync j = mddev->resyncmin while (j < maxsectors) sectors = raid10syncrequest(mddev, j, &skipped) if (!mdbitmapstartsync(..., &syncblocks)) // mdbitmapstartsync set syncblocks to 0 return syncblocks + sectorsskippe; // sectors = 0; j += sectors; // j never change

Root cause is that commit 301867b1c168 ("md/raid10: check slab-out-of-bounds in mdbitmapgetcounter") return early from mdbitmapgetcounter(), without setting returned blocks.

Fix this problem by always set returned blocks from mdbitmapgetcounter"(), as it used to be.

Noted that this patch just fix the softlockup problem in kernel, the case that bitmap size doesn't match array size still need to be fixed.