[PATCH 36/64] scsi: ibmvscsi: Avoid multi-field memset() overflow by aiming at srp

[Tyrel Datwyler]

On 7/28/21 8:35 PM, Martin K. Petersen wrote:
> 
> Kees,
> 
>> For example, change it to:
>>
>> +	BUILD_BUG_ON(sizeof(evt_struct->iu.srp) != SRP_MAX_IU_LEN);
>> +	memset(&evt_struct->iu.srp, 0x00, sizeof(evt_struct->iu.srp));
>>  	srp_cmd = &evt_struct->iu.srp.cmd;
>> -	memset(srp_cmd, 0x00, SRP_MAX_IU_LEN);
> 
>> For the moment, I'll leave the patch as-is unless you prefer having
>> the BUILD_BUG_ON(). :)
> 
> I'm OK with the BUILD_BUG_ON(). Hopefully Tyrel or Brian will chime in.
> 

All the other srp structs are at most 64 bytes and the size of the union is
explicitly set to SRP_MAX_IU_LEN by the last field of the union.

union srp_iu {
        struct srp_login_req login_req;
        struct srp_login_rsp login_rsp;
        struct srp_login_rej login_rej;
        struct srp_i_logout i_logout;
        struct srp_t_logout t_logout;
        struct srp_tsk_mgmt tsk_mgmt;
        struct srp_cmd cmd;
        struct srp_rsp rsp;
        u8 reserved[SRP_MAX_IU_LEN];
};

So, in my mind if SRP_MAX_IU_LEN ever changes so does the size of the union
making the BUILD_BUG_ON() superfluous. But it doesn't really hurt anything either.

-Tyrel