CVE-2024-26962

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

dm-raid456, md/raid456: fix a deadlock for dm-raid456 while io concurrent with reshape

For raid456, if reshape is still in progress, then IO across reshape position will wait for reshape to make progress. However, for dm-raid, in following cases reshape will never make progress hence IO will hang:

1) the array is read-only; 2) MDRECOVERYWAIT is set; 3) MDRECOVERYFROZEN is set;

After commit c467e97f079f ("md/raid6: use valid sector values to determine if an I/O should wait on the reshape") fix the problem that IO across reshape position doesn't wait for reshape, the dm-raid test shell/lvconvert-raid-reshape.sh start to hang:

[root@fedora ~]# cat /proc/979/stack [<0>] waitwoken+0x7d/0x90 [<0>] raid5makerequest+0x929/0x1d70 [raid456] [<0>] mdhandlerequest+0xc2/0x3b0 [mdmod] [<0>] raidmap+0x2c/0x50 [dmraid] [<0>] _mapbio+0x251/0x380 [dmmod] [<0>] dmsubmitbio+0x1f0/0x760 [dmmod] [<0>] _submitbio+0xc2/0x1c0 [<0>] submitbionoacctnocheck+0x17f/0x450 [<0>] submitbionoacct+0x2bc/0x780 [<0>] submitbio+0x70/0xc0 [<0>] mpagereadahead+0x169/0x1f0 [<0>] blkdevreadahead+0x18/0x30 [<0>] readpages+0x7c/0x3b0 [<0>] pagecacheraunbounded+0x1ab/0x280 [<0>] forcepagecachera+0x9e/0x130 [<0>] pagecachesyncra+0x3b/0x110 [<0>] filemapgetpages+0x143/0xa30 [<0>] filemapread+0xdc/0x4b0 [<0>] blkdevreaditer+0x75/0x200 [<0>] vfsread+0x272/0x460 [<0>] ksysread+0x7a/0x170 [<0>] _x64sysread+0x1c/0x30 [<0>] dosyscall64+0xc6/0x230 [<0>] entrySYSCALL64afterhwframe+0x6c/0x74

This is because reshape can't make progress.

For md/raid, the problem doesn't exist because register new sync_thread doesn't rely on the IO to be done any more:

1) If array is read-only, it can switch to read-write by ioctl/sysfs; 2) md/raid never set MDRECOVERYWAIT; 3) If MDRECOVERYFROZEN is set, mddevsuspend() doesn't hold 'reconfigmutex', hence it can be cleared and reshape can continue by sysfs api 'sync_action'.

However, I'm not sure yet how to avoid the problem in dm-raid yet. This patch on the one hand make sure raidmessage() can't change syncthread() through raidmessage() after presuspend(), on the other hand detect the above 3 cases before wait for IO do be done in dmsuspend(), and let dm-raid requeue those IO.