Re: [PATCH v3] scsi: core: fix uninit-value access of variable sshdr

["zhengbin (A)" <zhengbin13@huawei.com>]

On 2019/10/17 8:05, Finn Thain wrote:
> On Sat, 12 Oct 2019, zhengbin wrote:
>
>> kmsan report a warning in 5.1-rc4:
>>
>> BUG: KMSAN: uninit-value in sr_get_events drivers/scsi/sr.c:207 [inline]
>> BUG: KMSAN: uninit-value in sr_check_events+0x2cf/0x1090 drivers/scsi/sr.c:243
>> CPU: 1 PID: 13858 Comm: syz-executor.0 Tainted: G    B             5.1.0-rc4+ #8
>> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Ubuntu-1.8.2-1ubuntu1 04/01/2014
>> Call Trace:
>>  __dump_stack lib/dump_stack.c:77 [inline]
>>  dump_stack+0x173/0x1d0 lib/dump_stack.c:113
>>  kmsan_report+0x131/0x2a0 mm/kmsan/kmsan.c:619
>>  __msan_warning+0x7a/0xf0 mm/kmsan/kmsan_instr.c:310
>>  sr_get_events drivers/scsi/sr.c:207 [inline]
>>  sr_check_events+0x2cf/0x1090 drivers/scsi/sr.c:243
>>
>> The reason is as follows:
>> sr_get_events
>>   struct scsi_sense_hdr sshdr;  -->uninit
>>   scsi_execute_req              -->If fail, will not set sshdr
>>   scsi_sense_valid(&sshdr)      -->access sshdr
>>
>> We can init sshdr in sr_get_events, but there have many callers of
>> scsi_execute, scsi_execute_req, we have to troubleshoot all callers,
>> the simpler way is init sshdr in __scsi_execute.
>>
>> BTW: sr_do_ioctl should check whether sshdr is valid, fix this
>>
>> Signed-off-by: zhengbin <zhengbin13@huawei.com>
>> ---
>> v1->v2: modify the comments suggested by Bart
>> v2->v3: fix bug in sr_do_ioctl
>>  drivers/scsi/scsi_lib.c | 7 +++++++
>>  drivers/scsi/sr_ioctl.c | 5 +++++
>>  2 files changed, 12 insertions(+)
>>
>> diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
>> index 5447738..d5e29c5 100644
>> --- a/drivers/scsi/scsi_lib.c
>> +++ b/drivers/scsi/scsi_lib.c
>> @@ -255,6 +255,13 @@ int __scsi_execute(struct scsi_device *sdev, const unsigned char *cmd,
>>  	struct scsi_request *rq;
>>  	int ret = DRIVER_ERROR << 24;
>>
>> +	/*
>> +	 * Zero-initialize sshdr for those callers that check the *sshdr
>> +	 * contents even if no sense data is available.
>> +	 */
>> +	if (sshdr)
>> +		memset(sshdr, 0, sizeof(struct scsi_sense_hdr));
>> +
>>  	req = blk_get_request(sdev->request_queue,
>>  			data_direction == DMA_TO_DEVICE ?
>>  			REQ_OP_SCSI_OUT : REQ_OP_SCSI_IN, BLK_MQ_REQ_PREEMPT);
> Does this have any effect? It appears __scsi_execute() calls 
> scsi_normalize_sense(), which already does
> memset(sshdr, 0, sizeof(struct scsi_sense_hdr)).

__scsi_execute

  if (IS_ERR(req))  -->not init

    return ret;


  if (bufflen && ...) -->not init

    goto out;


scsi_normalize_sense

>