Re: [PATCH] scsi: scsi_debug: fix return checks for kcalloc

[Joe Perches <joe@perches.com>]

On Wed, 2021-11-03 at 14:01 -0500, George Kennedy wrote:
> Change return checks from kcalloc() to now check for NULL and
> ZERO_SIZE_PTR using the ZERO_OR_NULL_PTR macro or the following
> crash can occur if ZERO_SIZE_PTR indicator is returned.
> 
> BUG: KASAN: null-ptr-deref in memcpy include/linux/fortify-string.h:191 [inline]
> BUG: KASAN: null-ptr-deref in sg_copy_buffer+0x138/0x240 lib/scatterlist.c:974
> Write of size 4 at addr 0000000000000010 by task syz-executor.1/22789
[]
> diff --git a/drivers/scsi/scsi_debug.c b/drivers/scsi/scsi_debug.c
[]
> @@ -3909,7 +3909,7 @@ static int resp_comp_write(struct scsi_cmnd *scp,
>  		return ret;
>  	dnum = 2 * num;
>  	arr = kcalloc(lb_size, dnum, GFP_ATOMIC);
> -	if (NULL == arr) {
> +	if (ZERO_OR_NULL_PTR(arr)) {
>  		mk_sense_buffer(scp, ILLEGAL_REQUEST, INSUFF_RES_ASC,
>  				INSUFF_RES_ASCQ);
>  		return check_condition_result;

This one isn't necessary as num is already tested for non-0 above
this block.

> @@ -4265,7 +4265,7 @@ static int resp_verify(struct scsi_cmnd *scp, struct sdebug_dev_info *devip)
>  		return ret;
>  
>  	arr = kcalloc(lb_size, vnum, GFP_ATOMIC);
> -	if (!arr) {
> +	if (ZERO_OR_NULL_PTR(arr)) {
>  		mk_sense_buffer(scp, ILLEGAL_REQUEST, INSUFF_RES_ASC,
>  				INSUFF_RES_ASCQ);
>  		return check_condition_result;

Here it's probably clearer code to test vnum == 0 before the kcalloc
and return check_condition_result;

> @@ -4334,7 +4334,7 @@ static int resp_report_zones(struct scsi_cmnd *scp,
>  			    max_zones);
>  
>  	arr = kcalloc(RZONES_DESC_HD, alloc_len, GFP_ATOMIC);
> -	if (!arr) {
> +	if (ZERO_OR_NULL_PTR(arr)) {
>  		mk_sense_buffer(scp, ILLEGAL_REQUEST, INSUFF_RES_ASC,
>  				INSUFF_RES_ASCQ);
>  		return check_condition_result;

And here test alloc_len == 0 before the kcalloc.