CVE-2022-50373: fs: dlm: fix race in lowcomms

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

fs: dlm: fix race in lowcomms

This patch fixes a race between queuework() in dlmlowcommscommitmsg() and srcureadunlock(). The queuework() can take the final reference of a dlmmsg and so msg->idx can contain garbage which is signaled by the following warning:

[ 676.237050] ------------[ cut here ]------------ [ 676.237052] WARNING: CPU: 0 PID: 1060 at include/linux/srcu.h:189 dlmlowcommscommitmsg+0x41/0x50 [ 676.238945] Modules linked in: dlmlocktorture torture rpcsecgsskrb5 intelraplmsr intelraplcommon iTCOwdt iTCOvendorsupport qxl kvmintel drmttmhelper vmwvsockvirtiotransport kvm vmwvsockvirtiotransportcommon ttm irqbypass crc32pclmul joydev crc32cintel serioraw drmkmshelper vsock virtioscsi virtioconsole virtioballoon sndpcm drm syscopyarea sysfillrect sysimgblt sndtimer fbsysfops i2ci801 lpcich snd i2csmbus soundcore pcspkr [ 676.244227] CPU: 0 PID: 1060 Comm: locktorturewr Not tainted 5.19.0-rc3+ #1546 [ 676.245216] Hardware name: Red Hat KVM/RHEL-AV, BIOS 1.16.0-2.module+el8.7.0+15506+033991b0 04/01/2014 [ 676.246460] RIP: 0010:dlmlowcommscommitmsg+0x41/0x50 [ 676.247132] Code: fe ff ff ff 75 24 48 c7 c6 bd 0f 49 bb 48 c7 c7 38 7c 01 bd e8 00 e7 ca ff 89 de 48 c7 c7 60 78 01 bd e8 42 3d cd ff 5b 5d c3 <0f> 0b eb d8 66 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 55 48 [ 676.249253] RSP: 0018:ffffa401c18ffc68 EFLAGS: 00010282 [ 676.249855] RAX: 0000000000000001 RBX: 00000000ffff8b76 RCX: 0000000000000006 [ 676.250713] RDX: 0000000000000000 RSI: ffffffffbccf3a10 RDI: ffffffffbcc7b62e [ 676.251610] RBP: ffffa401c18ffc70 R08: 0000000000000001 R09: 0000000000000001 [ 676.252481] R10: 0000000000000001 R11: 0000000000000001 R12: 0000000000000005 [ 676.253421] R13: ffff8b76786ec370 R14: ffff8b76786ec370 R15: ffff8b76786ec480 [ 676.254257] FS: 0000000000000000(0000) GS:ffff8b7777800000(0000) knlGS:0000000000000000 [ 676.255239] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 676.255897] CR2: 00005590205d88b8 CR3: 000000017656c003 CR4: 0000000000770ee0 [ 676.256734] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 [ 676.257567] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 [ 676.258397] PKRU: 55555554 [ 676.258729] Call Trace: [ 676.259063] <TASK> [ 676.259354] dlmmidcommscommitmhandle+0xcc/0x110 [ 676.259964] queuebast+0x8b/0xb0 [ 676.260423] grantpendinglocks+0x166/0x1b0 [ 676.261007] unlocklock+0x75/0x90 [ 676.261469] unlocklock.isra.57+0x62/0xa0 [ 676.262009] dlmunlock+0x21e/0x330 [ 676.262457] ? locktorturestats+0x80/0x80 [dlmlocktorture] [ 676.263183] tortureunlock+0x5a/0x90 [dlmlocktorture] [ 676.263815] ? preemptcountsub+0xba/0x100 [ 676.264361] ? complete+0x1d/0x60 [ 676.264777] locktorturewriter+0xb8/0x150 [dlmlocktorture] [ 676.265555] kthread+0x10a/0x130 [ 676.266007] ? kthreadcompleteandexit+0x20/0x20 [ 676.266616] retfromfork+0x22/0x30 [ 676.267097] </TASK> [ 676.267381] irq event stamp: 9579855 [ 676.267824] hardirqs last enabled at (9579863): [<ffffffffbb14e6f8>] upconsolesem+0x58/0x60 [ 676.268896] hardirqs last disabled at (9579872): [<ffffffffbb14e6dd>] upconsolesem+0x3d/0x60 [ 676.270008] softirqs last enabled at (9579798): [<ffffffffbc200349>] dosoftirq+0x349/0x4c7 [ 676.271438] softirqs last disabled at (9579897): [<ffffffffbb0d54c0>] irqexitrcu+0xb0/0xf0 [ 676.272796] ---[ end trace 0000000000000000 ]---

I reproduced this warning with dlmlocktorture test which is currently not upstream. However this patch fix the issue by make a additional refcount between dlmlowcommsnewmsg() and dlmlowcommscommitmsg(). In case of the race the krefput() in dlmlowcommscommitmsg() will be the final put.