Re: [PATCH] scsi: core: fix bad pointer dereference when ehandler kthread is invalid

[Ming Lei <ming.lei@redhat.com>]

On Thu, Jul 01, 2021 at 01:56:59PM -0600, Tyrel Datwyler wrote:
> Commit 66a834d ("scsi: core: Fix error handling of scsi_host_alloc()")
> changed the allocation logic to call put_device() to perform host
> cleanup with the assumption that IDA removal and stopping the kthread
> would properly be peformed in scsi_host_dev_release(). However, in the
> unlikely case that the error handler thread fails to spawn
> shost->ehandler is set to ERR_PTR(-ENOMEM). The error handler cleanup
> code in scsi_host_dev_release() will call kthread_stop() if
> shost->ehandler != NULL which will always be the case whether the
> kthread was succesfully spawned or not. In the case that it failed to
> spawn this has the nasty side effect of trying to dereference an
> invalid pointer when kthread_stop() is called. The follwing splat
> provides an example of this behavior in the wild:
> 
> scsi host11: error handler thread failed to spawn, error = -4
> Kernel attempted to read user page (10c) - exploit attempt? (uid: 0)
> BUG: Kernel NULL pointer dereference on read at 0x0000010c
> Faulting instruction address: 0xc00000000818e9a8
> Oops: Kernel access of bad area, sig: 11 [#1]
> LE PAGE_SIZE=64K MMU=Hash SMP NR_CPUS=2048 NUMA pSeries
> Modules linked in: ibmvscsi(+) scsi_transport_srp dm_multipath dm_mirror dm_region
>  hash dm_log dm_mod fuse overlay squashfs loop
> CPU: 12 PID: 274 Comm: systemd-udevd Not tainted 5.13.0-rc7 #1
> NIP:  c00000000818e9a8 LR: c0000000089846e8 CTR: 0000000000007ee8
> REGS: c000000037d12ea0 TRAP: 0300   Not tainted  (5.13.0-rc7)
> MSR:  800000000280b033 <SF,VEC,VSX,EE,FP,ME,IR,DR,RI,LE>  CR: 28228228
> XER: 20040001
> CFAR: c0000000089846e4 DAR: 000000000000010c DSISR: 40000000 IRQMASK: 0
> GPR00: c0000000089846e8 c000000037d13140 c000000009cc1100 fffffffffffffffc
> GPR04: 0000000000000001 0000000000000000 0000000000000000 c000000037dc0000
> GPR08: 0000000000000000 c000000037dc0000 0000000000000001 00000000fffff7ff
> GPR12: 0000000000008000 c00000000a049000 c000000037d13d00 000000011134d5a0
> GPR16: 0000000000001740 c0080000190d0000 c0080000190d1740 c000000009129288
> GPR20: c000000037d13bc0 0000000000000001 c000000037d13bc0 c0080000190b7898
> GPR24: c0080000190b7708 0000000000000000 c000000033bb2c48 0000000000000000
> GPR28: c000000046b28280 0000000000000000 000000000000010c fffffffffffffffc
> NIP [c00000000818e9a8] kthread_stop+0x38/0x230
> LR [c0000000089846e8] scsi_host_dev_release+0x98/0x160
> Call Trace:
> [c000000033bb2c48] 0xc000000033bb2c48 (unreliable)
> [c0000000089846e8] scsi_host_dev_release+0x98/0x160
> [c00000000891e960] device_release+0x60/0x100
> [c0000000087e55c4] kobject_release+0x84/0x210
> [c00000000891ec78] put_device+0x28/0x40
> [c000000008984ea4] scsi_host_alloc+0x314/0x430
> [c0080000190b38bc] ibmvscsi_probe+0x54/0xad0 [ibmvscsi]
> [c000000008110104] vio_bus_probe+0xa4/0x4b0
> [c00000000892a860] really_probe+0x140/0x680
> [c00000000892aefc] driver_probe_device+0x15c/0x200
> [c00000000892b63c] device_driver_attach+0xcc/0xe0
> [c00000000892b740] __driver_attach+0xf0/0x200
> [c000000008926f28] bus_for_each_dev+0xa8/0x130
> [c000000008929ce4] driver_attach+0x34/0x50
> [c000000008928fc0] bus_add_driver+0x1b0/0x300
> [c00000000892c798] driver_register+0x98/0x1a0
> [c00000000810eb60] __vio_register_driver+0x80/0xe0
> [c0080000190b4a30] ibmvscsi_module_init+0x9c/0xdc [ibmvscsi]
> [c0000000080121d0] do_one_initcall+0x60/0x2d0
> [c000000008261abc] do_init_module+0x7c/0x320
> [c000000008265700] load_module+0x2350/0x25b0
> [c000000008265cb4] __do_sys_finit_module+0xd4/0x160
> [c000000008031110] system_call_exception+0x150/0x2d0
> [c00000000800d35c] system_call_common+0xec/0x278
> 
> Fix this be nulling shost->ehandler when the kthread fails to spawn.
> 
> Cc: stable@vger.kernel.org
> Fixes: 66a834d ("scsi: core: Fix error handling of scsi_host_alloc()")
> Signed-off-by: Tyrel Datwyler <tyreld@linux.ibm.com>

Reviewed-by: Ming Lei <ming.lei@redhat.com>


Thanks,
Ming