CVE-2021-46938

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

dm rq: fix double free of blkmqtag_set in dev remove after table load fails

When loading a device-mapper table for a request-based mapped device, and the allocation/initialization of the blkmqtag_set for the device fails, a following device remove will cause a double free.

E.g. (dmesg): device-mapper: core: Cannot initialize queue for request-based dm-mq mapped device device-mapper: ioctl: unable to set up device queue for new table. Unable to handle kernel pointer dereference in virtual kernel address space Failing address: 0305e098835de000 TEID: 0305e098835de803 Fault in home space mode while using kernel ASCE. AS:000000025efe0007 R3:0000000000000024 Oops: 0038 ilc:3 [#1] SMP Modules linked in: ... lots of modules ... Supported: Yes, External CPU: 0 PID: 7348 Comm: multipathd Kdump: loaded Tainted: G W X 5.3.18-53-default #1 SLE15-SP3 Hardware name: IBM 8561 T01 7I2 (LPAR) Krnl PSW : 0704e00180000000 000000025e368eca (kfree+0x42/0x330) R:0 T:1 IO:1 EX:1 Key:0 M:1 W:0 P:0 AS:3 CC:2 PM:0 RI:0 EA:3 Krnl GPRS: 000000000000004a 000000025efe5230 c1773200d779968d 0000000000000000 000000025e520270 000000025e8d1b40 0000000000000003 00000007aae10000 000000025e5202a2 0000000000000001 c1773200d779968d 0305e098835de640 00000007a8170000 000003ff80138650 000000025e5202a2 000003e00396faa8 Krnl Code: 000000025e368eb8: c4180041e100 lgrl %r1,25eba50b8 000000025e368ebe: ecba06b93a55 risbg %r11,%r10,6,185,58 #000000025e368ec4: e3b010000008 ag %r11,0(%r1)

000000025e368eca: e310b0080004 lg %r1,8(%r11) 000000025e368ed0: a7110001 tmll %r1,1 000000025e368ed4: a7740129 brc 7,25e369126 000000025e368ed8: e320b0080004 lg %r2,8(%r11) 000000025e368ede: b904001b lgr %r1,%r11 Call Trace: [<000000025e368eca>] kfree+0x42/0x330 [<000000025e5202a2>] blkmqfreetagset+0x72/0xb8 [<000003ff801316a8>] dmmqcleanupmappeddevice+0x38/0x50 [dmmod] [<000003ff80120082>] freedev+0x52/0xd0 [dmmod] [<000003ff801233f0>] _dmdestroy+0x150/0x1d0 [dmmod] [<000003ff8012bb9a>] devremove+0x162/0x1c0 [dmmod] [<000003ff8012a988>] ctlioctl+0x198/0x478 [dmmod] [<000003ff8012ac8a>] dmctlioctl+0x22/0x38 [dmmod] [<000000025e3b11ee>] ksysioctl+0xbe/0xe0 [<000000025e3b127a>] _s390xsysioctl+0x2a/0x40 [<000000025e8c15ac>] systemcall+0xd8/0x2c8 Last Breaking-Event-Address: [<000000025e52029c>] blkmqfreetagset+0x6c/0xb8 Kernel panic - not syncing: Fatal exception: paniconoops

When allocation/initialization of the blkmqtagset fails in dmmqinitrequestqueue(), it is uninitialized/freed, but the pointer is not reset to NULL; so when devremove() later gets into dmmqcleanupmappeddevice() it sees the pointer and tries to uninitialize and free it again.

Fix this by setting the pointer to NULL in dmmqinitrequestqueue() error-handling. Also set it to NULL in dmmqcleanupmappeddevice().